Landracing Forum
Tech Information => Technical Discussion => Topic started by: Jack Gifford on January 07, 2014, 02:54:23 AM
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Needing to have a crank machined from billet for my lakester's four-cylinder engine may be the excuse I need to experiment with a novel (eccentric?) scheme for minimizing crank windage. The common knife-edging of counterweights, in my view, doesn't eliminate the majority of the turbulence created by weights (and similarly, any un-weighted crank webs). I intend to convert all of my crank's webs (all eight will be counterweights) to full-circles by attaching light weight "filler" segments (aluminum? magnesium? carbon fiber?) to the weights. I'm looking at various attachment schemes, from the standpoints of margin-of-safety retention (to reliably withstand about 8,500 G's!) and that the special machining can be done mostly on my mill.
Of course the primary turbulence-generators- rod journals, rods, and pistons- can't be eliminated, but the crank webs/weights are not an insignificant contribution.
My main reason for posting this: to learn about any prior efforts like this. Anybody know any examples? (other than full-flywheel style built-up cranks)
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Jack,
I've never heard of such a setup being utilized or tested, although I do not know everybody/everything. There are DRAMATIC gains to be had by reducing and/or eliminating "windage". The most productive avenue for windage reduction I have seen, is to use an oversized dry sump pump system to create negative crankcase pressure. Negative crankcase pressure creates other "opportunities" for power gains, in addition to creating a myriad of seal and gasket issues that need to be addressed. You will need to create about -5/-15 inches of water pressure for a useful gain. At these negative pressures, air influx to the crankcase becomes a serious sealing issue . . . . . .
Some issues to consider for your setup:
1/ A fully "rounded" counterweight might eliminate the "churning", but some windage will still result from "surface attachment". The best results I've seen use a combination of polished surfaces, crank "scraper(s)", windage tray(s), and the aforementioned oversized scavenge pump(s) to remove the frothy oil from the crankcase as rapidly as practical.
2/ Even with the lightest mass of "filler segments" engine balance will, of course, be affected. There may be some clever way to negate any harmful balance factor issues for your engine configuration. If not, you may want to analyse whether the possible benefit will be. worth the effort. Thinking of the problem in linear terms, what percentage of the "exposed" crankshaft length is purely rotational Vs. the percentage that is rotational/reciprocal?
3/ How can the "filler segments" be "effectively retained"? The figure you mentioned of 8500 G's, is that a calculated number or a speculative number? Of the racing engines I have been involved with, the engineering/design limits are typically 5000/5200 G's maximum. And there are various material failures at those values. Perhaps you can calculate the load in pounds/feet. Very high loads will have a very limited useful life in terms of cycles to failure. Think drag racing connecting rods. Failures of this type will be both spectacular and expensive. I like tension loads as low as possible, and under a max of 12,500 pounds/feet. At loads of 15,000 pounds/feet and upwards, material failure is annoyingly common. Between 12,500 and 15,000 pounds/feet is drag race/crap shoot territory, using the best (the most expensive) material(s) available.
4/ Will the engine configuration be inherently balanced? (ie: flat opposed four cyl, etc.) Or, inherently unbalanced? (ie: inline four cyl, V-twin, flat plane crank V-8, etc.) Vibrations and torsionals can really play hell with parts attached with fasteners.
Just my two cents. Hope this helps you out.
:cheers:
Fordboy
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"Comet" GoKart engines all have a polyethylene stuffer riveted onto the cranks. They are machined smooth and round to make a disc. Those engines work just fine up 13500 RPMs, although I tried 18000 and the engine bought the farm when the plastic came apart.
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Fordboy;
Re: Your point #4: Horizontally opposed 4-cylinder engines are not inherently balanced; there is a couple in the horizontal plane. A 6-cylinder in-line engine is inherently balanced; so is a V-12. Those are sweet. Why Dodge developed a V-10 is beyond me-- it could have been a V-12.
Regards, Neil Tucson, Az
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I agree that regardless of how effective the nose & tail shape are, an un-interrupted cylinder generates less drag.
A low density stuffer sounds good, don't know enough about the attachment method to comment.
JM2¢?
How about a hollow box of 16 gauge sheet, welded in place? As long as the box is liquid-tight it doesn't need to have continuous attachment.
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The effort will outweigh the reward.
My 2c. 8-)
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That places staying home above building cars, doesn't it?
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Fordboy,
Your use of the units “pounds/feet” is puzzling. It seems to be intended to indicate stress levels, and the numerical amounts discussed seem to correlate with stresses expressed as “pounds/square inch”, but “pounds/feet” has me stumped.
Back to windage--
I would agree with Fordboy that it is probably much easier and more effective to eliminate the wind rather than try to create an ineffective propeller. If there is little fluid to churn, one gains from not only the counterweights, but also the throws, connecting rods, piston pumping etc.
A clean disc vs. conventional counterweights comparison might be a nice CFD exercise--which could likely give a quantitative indication of any gains that might be obtained.
And I agree with Taurek that, in actuality, the effort will outweigh the possible rewards. Seriously messing with a high speed crankshaft is playing with fire.
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... That places staying home above building cars, doesn't it?...
That would be my response to "is it worth the effort?". After many years of blown-alky competition (up to 9,000 RPM), using all the common remedies for windage effects (aerated oil, etc.), I'll gladly put lots of effort into this experiment.
Thanks for the responses. I'll try to answer some of the concerns:
> Dry sump- that's a given for this project (along with windage tray and scraper). But like my other hemi (V8), I won't be pulling more than about 3 in.Hg. depression in the crankcase. Sizing the scavenge pump larger creates more oil aeration (by nature of any drysump system). As for reducing the density of the crankcase "fluid" (mostly air) via more scavenging, I see that as a pretty insignificant contribution to windage reduction.
> Surface attachment- order of magnitude smaller effect than going to full-round.
> My additions will maintain the center-of-mass of each counterweight at its original location, thus will not alter the balancing considerations.
> I acknowledged in my original post that nothing can be done about windage created by the reciprocating stuff. But this still leaves "interrupted" counterweights as a very significant factor.
> Radial acceleration of 8,500 G is calculated- 10,000 RPM, but +/- about 5% on radial distances of filler-segment centers-of-mass from crank centerline. Acceleration vectors other than radial are not known (would need comprehensive torsional displacement analysis throughout the crank), but I can almost guarantee they would be at least one order of magnitude less than radial.
> Cycles to failure- just for a moment, ignore any crank twisting, and consider this example: say I make a clean run, accelerating the engine to some speed, then decelerate to a stop. That whole run would cause one cycle of stress in my attachments, while the reciprocating pieces underwent many thousands of cycles. But, yes, cranks do dynamically twist- but do not create tangential accelerations on the order of 8,500 Gs.
> Hollow box construction- rigidity at 8,500 Gs could be problematic. Unless I got into ultra-expensive carbon-fiber science, which doesn't correspond with my shade-tree approach.
> I'm purposely not showing any attachment schemes, since I'm still studying various methods.
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Hi Jack
Spend your time building a flow bench and play with the intake & exhaust tracks, that could gain you a lot more HP that some air bumping up against the crankshaft bumps
Plus crankshaft harmonics are bad news!!!
G Don
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Fordboy;
Re: Your point #4: Horizontally opposed 4-cylinder engines are not inherently balanced; there is a couple in the horizontal plane. A 6-cylinder in-line engine is inherently balanced; so is a V-12. Those are sweet. Why Dodge developed a V-10 is beyond me-- it could have been a V-12.
Regards, Neil Tucson, Az
Neil,
After reviewing my Charles Taylor, you are correct. There also seem to be some other types inherently balanced. Inline 8, 90 degree crank, with a certain firing order. Along with some others, ie: flat 8, 180 degree crank, firing 2 cyl simultaneously; flat 12 with 60 degree crank; etc. Anyone wishing to inquire further should refer to: Volume 2, 'The Internal-Combustion Engine in Theory and Practice', pages 298/305 for self-gratification.
According to a reliable source I knew who was working for Dodge (Chrysler) at the time: "They wanted an advertising tie-in to F/1 technology."
V-10: equals 2 inline 5 cylinder engines coupled at the crank; OR, 5 V-twins coupled end to end to end, etc. Just goes to prove: You can come up with an "acceptable solution" to any problem. You just have to throw enough money at it . . . . . . . .
Oddly enough, 4 cycle inline 5's and V-10' engines are not listed in Taylor's book. They are however listed under 2 cycle engine possibilities . . . . .
:cheers:
F/B
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"should refer to: Volume 2, 'The Internal-Combustion Engine in Theory and Practice', pages 298/305 for self-gratification."
If I do -- will hair grow on my hands and I'll go blind? :evil: :evil: :cheers:
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That should have happened when you were 13!! :-P
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"should refer to: Volume 2, 'The Internal-Combustion Engine in Theory and Practice', pages 298/305 for self-gratification."
If I do -- will hair grow on my hands and I'll go blind? :evil: :evil: :cheers:
well.. not if you keep the hair worn off!
nothing for eyesight though... (carrots?)
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Regarding the V10 engines that came along in the 90s. I was at Cobo Hall for the SAE conference when EPA sat on the stage and we (manufacturers) sat in the chairs. It was the decision point for OBD2, and the most heated discussions centered around all-load, all-speed MISFIRE detection standards. Only AUDI had a pretty good working solution at that date, but it used a complicated sensor arrangement looking at both ends of the crankshaft, simultaneously, to take torsional twist calculations into the equation. That method would have been the death knell for manual transmissions.
An agreement was made to defer some measure of the requirement (misfire detection) for "more than 8 cylinder" engines. That moment was a head-start for getting some big displacement engines into the market, while buying some time for technology to catch up with aspects of OBD2 goals. For two manufacturers, large V10s were the cost-effective way to proceed, while another chose to back away from the extra-large engine for OBD2 level engine management......but....
.....Keep in mind, that there was allowance for delay of OBD2 application until '96 model year for any engine that was not fitted with a "newly designed engine management system" in '94-95 model years.
The mid-to-late 90s was an intense time for everyone in the industry; in any event, they all did a great job. Thats what I know of the whole V10 story, just from the emissions side of the puzzle.
JimL
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JimL, thank you for that bit of insight. Oftentimes decisions are made for reasons that are not apparent but that does not necessarily make them bad decisions. Apparently the V10 had a bit of that going on.
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Times and places have jumbled a bit, in my memory, so I cannot remember what year it was....I was in a contract shop looking at a row of beautifully forged and machined V12 crankshafts destined for GMs luxury line. I believe they were abandoned in view of the pending OBD2 regs, perhaps before the Misfire cylinder allowance was proposed. I am not for certain, but I think maybe about '89-90?
It may have been canceled due to cost or market issue for some model that would be limited sales potential.
So.....before it seems we run too far off the crank windage issue; one of the biggest improvements comes with shortening the stroke and pulling the counterweights inboard. It has an unmentioned side affect of reducing the pumping VELOCITY beneath each piston. That is a tremendous benefit.
Need proof? Many of the new "longer stroke ratio" production engines are resorting to ported main bearing webs to get control of the higher velocity lateral pumping in the crankcase. It turns out the air isnt just whirling around with the counterweights in a nice neat circle! Maybe that is why we dont seem to get much out of heavily modified counterweights.
Longer strokes are so violent that some new 4-cylinder engines now require dedicated oil separation chambers, in the side of the blocks. This to keep themselves alive with thinner oils and tighter HC emissions. Interestingly, this whole windage/oil vapor control issue gets better as the number of cylinders goes up. I have no idea why.
As usual, those sharp engineers are ahead of us on this one, also.... :-P
JimL
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We have discussed this before but isolating each piston bay and then having each section have its own dedicated section of the dry sump scavenging pump and if you make the scavenging sections very large or large and instead of being a gear pump it is a two lobe pump you can actually lower the pressure in the engine case low enough that the air density drops considerably and drag is proportional to air density so drag on the crank, rods and piston is reduced accordingly. All NASCAR, F1 etc are doing this now and per Roush Racing it is worth about 40 hp on a NASCAR engine at 9500. Part of that increase is supposed to be credited to improved piston ring sealing due to the case vacuum.
Large generators have their internals flooded in hydrogen, low density, to reduce aero drag on the rotating armature. Good for 2-3% efficiency increase.
Rex
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What about full circle steel flywheels with mallory weight on the sides opposite the throws? Heavy, but so what, it's not a drag race. Would the the extra weight dampen out harmonics?
Tom
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Seeing as you're running a V-8 crankcase and a custom 4 cylinder crank, all bets are off as to finding anything other than your own creation on this.
But because of the long throw and the cavernous air space that the Poncho block has, a scraper and any baffling you can devise to get your oil to a pickup would be prudent, even if it didn't give you a single pony.
I just started the order process for mine today -
http://crank-scrapers.com/
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Rex, looking at this "internal crankcase", which surrounds my crank tightly, do you think I can just close the rod access windows and scavenge that area safely? This is both cylinders into one case, with no way to separate them because the rods run next to each other on a single pin. There are no other openings, just two cutouts to access the rod nuts (what a pain to take pistons in and out!) and the right side piston oiler hole, seen in photo. The left side is a closed bearing plate, kind of like an Offy, with the piston oiler for the back cylinder built in.
The right block-case area is a big hole with just the oil pump in it. I may have room to add an additional stock oil pump to scavenge that small "internal crankcase". It would be easy to close the rod-nut access holes with simple sheet metal plates.
The rest of the question....can I just have the second oil pump pickup whatever it can get and dump it right back into the sump, or must it go to an oil separator externally?
Thank you, and anyone else with an opinion, for looking.
JimL
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Fordboy,
Your use of the units “pounds/feet” is puzzling. It seems to be intended to indicate stress levels, and the numerical amounts discussed seem to correlate with stresses expressed as “pounds/square inch”, but “pounds/feet” has me stumped.
Interested Observer,
It's the result of an imperfect and aging brain. My apologies to all reading this thread.
Instead of referencing Lb/ft; the correct reference should be using Lbf, pounds of force. These numbers can be referenced from Critical g Load values typically applied to the reciprocating parts of race engine assemblies. This is a pretty typical reference method for software used to model/analyze con rod strength, ring flutter, etc.
Most race con-rod manufacturers can give a prospective purchaser an idea of the maximum load in pounds their con-rod styles can withstand. This is useful information, but you have to ask nicely for it. And it helps make intelligent decisions about the mass/weight of other components.
:cheers:
Fordboy
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"should refer to: Volume 2, 'The Internal-Combustion Engine in Theory and Practice', pages 298/305 for self-gratification."
If I do -- will hair grow on my hands and I'll go blind? :evil: :evil: :cheers:
SSS,
That's exactly what I meant . . . . . . . Why do you think most racers wear glasses?
:cheers:
F/B
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Times and places have jumbled a bit, in my memory, so I cannot remember what year it was....I was in a contract shop looking at a row of beautifully forged and machined V12 crankshafts destined for GMs luxury line. I believe they were abandoned in view of the pending OBD2 regs, perhaps before the Misfire cylinder allowance was proposed. I am not for certain, but I think maybe about '89-90?
It may have been canceled due to cost or market issue for some model that would be limited sales potential.
So.....before it seems we run too far off the crank windage issue; one of the biggest improvements comes with shortening the stroke and pulling the counterweights inboard. Yes, very effective. It has an unmentioned side affect of reducing the pumping VELOCITY beneath each piston. That is a tremendous benefit. The best racing engine engineers are aware of this and design to take advantage of this benefit, although this is not the primary reasoning behind short strokes.
Need proof? Many of the new "longer stroke ratio" production engines are resorting to ported main bearing webs to get control of the higher velocity lateral pumping in the crankcase. It turns out the air isnt just whirling around with the counterweights in a nice neat circle! YES! And that air/oil mixture has to go somewhere! Highly pressurized wet sump crankcases can blow out gaskets and seals. Oil/air "froth" can also be "pumped" back up into the heads or prevent oil/air drainage from the heads to the crankcase. My experience is: The best situation is if all the "extra" oil/air is evacuated from the crankcase with properly sized scavenge pumps. Maybe that is why we dont seem to get much out of heavily modified counterweights. That is the result I saw with wet sumps in "any" configuration and why dry sumps replaced them.
Longer strokes are so violent that some new 4-cylinder engines now require dedicated oil separation chambers, in the side of the blocks. This to keep themselves alive with thinner oils and tighter HC emissions. Interestingly, this whole windage/oil vapor control issue gets better as the number of cylinders goes up. I have no idea why. Usually the improvement comes from the larger overall crankcase volume. A larger volume is more difficult to highly pressurize as a result of multi-piston movement. At least that's what we concluded at the time. 2001.
As usual, those sharp engineers are ahead of us on this one, also.... :-P
JimL
Jim,
Still a slow and crappy typist. A long time ago, in a galaxy far, far away, I did a LOT of development work on dry sump V-8's. I added my highlighted thoughts to your text, sorry.
:cheers:
Fordboy
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We have discussed this before but isolating each piston bay and then having each section have its own dedicated section of the dry sump scavenging pump and if you make the scavenging sections very large or large and instead of being a gear pump it is a two lobe pump you can actually lower the pressure in the engine case low enough that the air density drops considerably and drag is proportional to air density so drag on the crank, rods and piston is reduced accordingly. All NASCAR, F1 etc are doing this now and per Roush Racing it is worth about 40 hp on a NASCAR engine at 9500. Part of that increase is supposed to be credited to improved piston ring sealing due to the case vacuum.
Large generators have their internals flooded in hydrogen, low density, to reduce aero drag on the rotating armature. Good for 2-3% efficiency increase.
Rex
Rex,
The Nascar engines I know of are running about the equivalent of -15" water to "evacuate" the crankcase. The power increases typically come from lowered radial tension ring packages. The top piston ring is then "energized" by the pressure of combustion, creating a friction/drag savings during other portions of the process.
ALL piston rings "work" via the principle of pressure differential. Creating a higher "differential" by lowering the crankcase pressure allows clever engine builders/engineers to reduce the radial tension for all of the rings. Thereby saving friction/drag for a net horsepower increase at the flywheel. It is important to note that this horsepower was always "inside" the engine. The drag friction of the higher radial tension rings kept it from getting out to the flywheel.
The bhp number you quote is in the ballpark for 358 cubic inch V-8's turning those rpm's.
:cheers:
Fordboy
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Rex, looking at this "internal crankcase", which surrounds my crank tightly, do you think I can just close the rod access windows and scavenge that area safely? This is both cylinders into one case, with no way to separate them because the rods run next to each other on a single pin. There are no other openings, just two cutouts to access the rod nuts (what a pain to take pistons in and out!) and the right side piston oiler hole, seen in photo. The left side is a closed bearing plate, kind of like an Offy, with the piston oiler for the back cylinder built in.
The right block-case area is a big hole with just the oil pump in it. I may have room to add an additional stock oil pump to scavenge that small "internal crankcase". It would be easy to close the rod-nut access holes with simple sheet metal plates.
The rest of the question....can I just have the second oil pump pickup whatever it can get and dump it right back into the sump, or must it go to an oil separator externally?
It will depend on how "frothy" it is coming out of the crankcase. Heavily "frothed" oil will need to be de-aerated. All the engines I've worked on want to be lubed with oil Vs. a frothy mixture of oil & air. IMHO.
Thank you, and anyone else with an opinion, for looking.
JimL
Jim,
See the highlighted note above.
:cheers:
F/B
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Thank you very much. :cheers: Now I have some idea I am going in the right direction. As you can tell, the block volume, outside the crankcase, is HUGE on this engine, and the crankshaft is far above the sump area. It was originally designed to have an automatic transmission with the planetary/clutches on one side and the pump/valve body on the other. It wound up with a 5-speed and a great big hole to match. This volume may explain why this thing never seems to push oil out of a simple open breather. There is also a huge, mostly empty, back case attached to the block (vented into the main sump below the crankcase).
This volume deal also makes it sound like Jack Giffords block arrangement could be an interesting advantage compared to typical 4-cylinder engines.
Also...did you ever work with Dave Phillips? Just wondering.
Thanks again, everyone. I spent too many years learning emissions and its diagnostics for our techs, and not enough learning this fun stuff.
JimL
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... we dont seem to get much out of heavily modified counterweights...
Who is the "we" and where are these "examples"? The whole reason for me posting this topic was to find any such real world examples. (I don't consider knife-edging, etc. "heavily modified", compared with a full-circle configuration). I would truly appreciate being directed to any such examples. Thanks.
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... This volume deal also makes it sound like Jack Giffords block arrangement could be an interesting advantage compared to typical 4-cylinder engines...
I agree. I considered blocking off the unused cylinders, but quickly decided that additional crankcase volume is preferable, if for no other reason than reducing the magnitude of pressure fluctuations in the crankcase.
I suppose I should also ask for opinions about this crucial decision- whether or not to place four sparkplugs in the block-off plate of the unused cylinder bank. A friend (who did body/paint on my "Speed Queen") thinks it would be hilarious during tech... :roll:
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... we dont seem to get much out of heavily modified counterweights...
Who is the "we" and where are these "examples"? The whole reason for me posting this topic was to find any such real world examples. (I don't consider knife-edging, etc. "heavily modified", compared with a full-circle configuration). I would truly appreciate being directed to any such examples. Thanks.
Back in the 90's I had access to bhp/tq numbers for 350/358 cubic inch Cup engines. This was the period when Nascar engine development left wet sump technology behind. I do not recall the year Nascar finally allowed dry sump equipted engines. Needless to say, a lot of dry sump development took place ahead of that time.
Although I am still bound by a non-disclosure clause, and can't quote total numbers, I will list bhp differences between spec types.
For everyones edification, real world dyno test stand numbers/examples: (note: bhp numbers varied slightly from pull to pull, +/- 2 bhp approx.)
1/ Swinging door wet sump pan, no windage tray, std crank/rods X bhp
2/ As above, with windage tray X+10 bhp
3/ As above, add knife edged crank with "small c'weights" X+20 bhp (Small dia c'weights used tungsten inserts.)
4/ As above, add complicated crank scraper/windage tray X+30 bhp
Fully round c'weights (ala motorcycle cranks) were never used on any of the test mules I was aware of.
BTW, 10bhp = approx. 1.5% at this point . . . . . .
The problem with all of this is that on banking or in turns, etc, oil contained in the pan sloshes around and up into the spinning mass of the assembly, at the cost of power and reliability. Add ons like an "Accusump" system help reliability, but they temporarily add oil to the crankcase, costing power.
Every driver I've ever worked with hasn't been too keen about a "temporary" loss of bhp while racing door handle to door handle with another team . . . . . . . .
5/ First dry sump iteration, off the shelf parts, cranks as above, very close tolerance "scrapers" X + 80 bhp
6/ Dry sump iteration, circa 2003, including very complicated mods to "minimize" oil in the engine,
-15" (H2O) vacuum in engine, ALL parts mfg'd "in house", other internal mods to assembly to take advantage of changes: X + 125 bhp
Bhp gain, from #1 to #6: approximately 21 bhp/litre. Also note: that some of the gains were only related to the oil system in that the changes to the oil system permitted changes to be made elsewhere in the engine for useful bhp gains . . . . .
And just for a frame of reference, the approximate development cost was: 1.3 million dollars, parts only. I was never made aware of the salary or facility costs, but I know they weren't cheap.
IMHO, anything you can do to get the oil/air out of the engine, (not just the crankcase), and create a vacuum, will serve to benefit your purpose. The only caveat I would add is that certain parts, (valve springs, exhaust valve stems, cylinder walls, piston skirts, etc) are cooled/lubricated by "flung off" oil. You want to be sure that your oil removal process doesn't "starve" a component for cooling/lubrication. Trust me on this one, it is an issue.
Most of this may be moot for LSR, I don't know, I have very little LSR exposure. But like drag racing, oil in a wet sump pan HAS to surge to the rear during launch. Once that oil is entrapped in the spinning mass, I doubt that it might be "flung off" during the high speed portion of a run.
Hope this helps.
:cheers:
Fordboy
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Fordboy - the above is a very intriguing and informative exposition...
Since -15 inches of water is only about one-half psi, could you be prevailed upon to comment on the following?
How was the vacuum created?
What was the limitation on the vacuum level? Pumping capacity, leakage rates, pan collapse, blowby etc?
Hazard a guess on the relative contribution--reduced oil churn vs. reduced pressure windage?
What were the more troublesome vacuum sealing problems?
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I think in F1 they are actually taking the case pressure (vacuum) much lower than the -15 inches of water that Fordboy mentioned. Their scavenger pumps are literally 2 or 3 lobe vacuum pumps and they have one for each of the 4 sections of the engine, for a V8. They also provide a small orifice into each section such that the pumps do not go into cavitation and provide maximum vacuum. I have attached a pic of a typical F1 pump that has been section and as you can see the sections are pretty serious parts.
Rex
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F1 motors always amaze me,
with the short pistons, rock over must be huge and he ring seal must be compromised.
I can see why such large scavenge pumps are used.
Not to mention the speeds these pieces of jewelry spin.
I had over the years started using scrapers on the cranks and screens to keep the oil away from the bottom.
The erosion on the impact side of the scrapers is impressive, these being fairly small motors and less than 10k revs. (intentional revs)
J
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Is cavitation in the feed side oil pump a problem on wet sump engines with a lot of crankcase vacuum? It seems cavitation might happen before the desired oil pressure is obtained.
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... I should also ask for opinions about this crucial decision- whether or not to place four sparkplugs in the block-off plate of the unused cylinder bank. A friend (who did body/paint on my "Speed Queen") thinks it would be hilarious during tech... :roll:
C'mon guys- lighten up. Or isn't a little levity allowed in the 'TECH' forum?
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Well, I like the idea and it would be really neat if you could fit it with those clear, flashing, spark plug wires they used to sell.
JimL
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... I should also ask for opinions about this crucial decision- whether or not to place four sparkplugs in the block-off plate of the unused cylinder bank. A friend (who did body/paint on my "Speed Queen") thinks it would be hilarious during tech... :roll:
C'mon guys- lighten up. Or isn't a little levity allowed in the 'TECH' forum?
When you get 'em all wound up it's really hard to back 'em down again Jack! 8-) 8-) :-D
Besides which the subject is rather interesting as are some of the recent replies.
Pete
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Fordboy - the above is a very intriguing and informative exposition...
Since -15 inches of water is only about one-half psi, could you be prevailed upon to comment on the following?
How was the vacuum created?
Initial dry sump testing logged a decrease in blow-by cfm. This was unexpected. At that time, blow-by cfm, in conjunction with leakdown %, was being used to evaluate the "quality" of the dynamic/static piston ring sealing. Wider, off the shelf, scavenge stages were then tried, resulting in even lower blow-by cfm. That's when the light bulb went off and the "problems" started . . . . . . . . Eventually, even more scavenge stages were added. The type of scavenge pump becomes important here, due to the pumping efficiency differences between styles. Ie: gear style Vs. lobe & rotor style Vs. roots style. In the end, total vacuum was a result of scavenge capacity/efficiency, piston ring blow-by, AND, the "leakage rate" of air "allowed" back into the engine assembly. It was a "baby steps/mickey mouse" deal.
What was the limitation on the vacuum level?
Pumping capacity, At first there was a LOT of resistance from pump manufacturers. They "knew" we didn't need that much scavenge pumping capability. We solved that by finding a receptive manufacturer who was happy to sell us "stuff we didn't need".
leakage rates, EVERYTHING leaked at first. The bigger pumps would suck cork gaskets into the engines. Standard seals would "gulp" air. It was a major program just to get things sealed.
pan collapse, We never got to the point where that happened, the fabricated pans were probably stiff enough in section. The cork pan gaskets were a giant "pita", and were replaced by "reinforced" pan gaskets. Stamped rocker covers on the other hand, were not stiff enough to clamp cork gaskets, or any other gaskets in place.
blowby etc? With poor ring sealing, or a bad top ring, or a scuffed piston, the whole setup takes a dive.
Something you didn't ask about: We worked very hard to reduce "throw off" oil from various assemblies. This reduces the volume of flow to say, con-rod bearings, cam lobe/tappet faces, cam bearings, etc, etc. Let's just say that there is some "non-quantifiable risk" to doing this. It was a giant learning curve.
Hazard a guess on the relative contribution--reduced oil churn vs. reduced pressure windage? We had a block with a lexan "window" in the crankcase, one of my "brilliant" ideas. It was like trying to look at a hurricane, close up! Not something that was easy to quantify. Just a wild guess, I think we might have been getting a reduction of 50%, most of that from reduced "churn". The later setups yielded "smaller hurricanes".
What were the more troublesome vacuum sealing problems? The cork gaskets and stamped tin were by far the worst. The final solution was to replace all those pieces with parts that were "stiffer" and/or could apply more "clamp load". Look at a Cup engine now, no tin, no cork, only castings, O-rings, printed RTV gaskets, etc. Look at how valleys are sealed now, remember the old cork ends when the manifold sealed the valley? Initially, we just turned the crank seals backwards, a dead giveaway to what we were doing. Double-lip and eventually multi-lip seals solved that problem. Problem was we couldn't hide what we were doing on race engines. Don't ever let anyone tell you that there aren't any "spies" in Nascar . . . . . . .
Interested Observer, et all,
Still a slow and crappy typist. I've inserted comments in your text, sorry.
I have been away from the pressure of "racing every day of the year" for about 11 years now. Looking at a current Cup engine and just "speculating":
1/ As I said above, no tin, no cork, only castings, O-rings and printed RTV gaskets. Stuff that can be really sealed tightly . . . . . . .
2/ "Big" multistage scavenge pumps and scavenge lines . . . . . . . .
3/ Ask yourself, "Where did the engine breathers go?"
I would hazard a guess that the negative pressures now are much higher than what could be achieved 10/11 years ago, with a probable net bhp gain of ?
Reflecting back, I would say this as a caution to everyone who wants to be an engine specialist: For every insight I had, it turned out that some "dope" had to go through the drudgery of "developing" the concept into something useful. That "dope" was usually me, so be careful of what you wish for . . . . . . . .
Even something that sounds simple, like replacing a cork gasket, can become a huge task if there are no alternative parts available . . . . . . . . .
And, in spite of what most guys think, technological jumps in performance are mostly a triumph of development over design . . . . . . . Note that this requires time AND lots of money. Unless you have "unlimited time" and "unlimited money", my advice becomes: Stay with a well developed package if you actually want to get to the race track. If you want a modern "treatise" regarding development over design, read the Milwaukee Midget's Build Diary. Keep in mind that he started with an engine that had 60 years of "development" behind it and he was getting advice and parts from well thought of suppliers. . . . . . . . I'm pretty sure he is a lot more satisfied with his effort of 2013 than with his previous efforts. But, you could ask him directly.
If you want to tinker around/fix stuff because that's what you enjoy, well that's a different deal, and you are on your own.
:cheers: :cheers:
Fordboy
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F1 motors always amaze me,
with the short pistons, rock over must be huge and he ring seal must be compromised.
If the ring seal is compromised, then lowered bhp must result. My guess is that the rock-over is well controlled and much less than you might imagine. In spite of the huge rpm's, the short stroke and relatively long con-rod length keeps the forces @ TDC overlap within reasonable limits.
I can see why such large scavenge pumps are used.
Not to mention the speeds these pieces of jewelry spin.
I had over the years started using scrapers on the cranks and screens to keep the oil away from the bottom.
The erosion on the impact side of the scrapers is impressive, these being fairly small motors and less than 10k revs. (intentional revs)
J
J,
See my note in your text.
:cheers:
F/B
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Is cavitation in the feed side oil pump a problem on wet sump engines with a lot of crankcase vacuum? It seems cavitation might happen before the desired oil pressure is obtained.
W/Walrus,
In my experience, cavitation is typically present within scavenge pumps. Scavenge pumps produce a mixture of oil & air (froth) which isn't a very good lubricant for plain bearings. (Non-roller bearings) This is why you typically see a separate pressure stage (or separate pressure pump) fed from a de-aerated oil tank on racing engines. Centrifuge type air/oil separators have been in use on high rpm racing engines for decades. Ie: Cosworth DFV. And I'm sure there are others.
IMHO, a single stage oil pump is a bad idea for any heavily stressed racing engine. They tend to go bang, rather unpredictably.
:cheers:
F/B
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I have a friend who started building oil pumps for Cup teams. There was a separate stage for separating air and oil. It was rather complex and required an immense amount of development time. At the prices he charges I know Cup engine development isn't cheap!
Pete
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Is cavitation in the feed side oil pump a problem on wet sump engines with a lot of crankcase vacuum? It seems cavitation might happen before the desired oil pressure is obtained.
If you're pulling a vacuum on a sealed wet sump motor, the oil pump is pumping from a lower pressure to the same lower pressure at the bearings. I can't see how it knows any difference. Relative pump pressure should remain the same. Your gauge will read lower because it will be comparing the lower absolute pump pressure to outside ambient pressure. For example, if your pump will pump 60psi normally, and now you're pulling a negative 5psi on your crankcase, your pump will be pumping from -5 psi, but since the entire crankcase is at -5psi, it will just put out 55psi gauge (still a difference of 60psi). Shouldn't be a problem. Dry sump may be a different situation because you have a separate scavenge pump which, if pumping into an external tank vented to the atmosphere, will have to overcome the vacuum to return the oil to the tank, at least on motorcycle systems.
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If you want a modern "treatise" regarding development over design, read the Milwaukee Midget's Build Diary. Keep in mind that he started with an engine that had 60 years of "development" behind it and he was getting advice and parts from well thought of suppliers. . . . . . . . I'm pretty sure he is a lot more satisfied with his effort of 2013 than with his previous efforts. But, you could ask him directly.
Happier? Absolutely.
Satisfied? I’m 3.087 mph shy of satisfied.
2010 – having to start somewhere . . .
(http://i361.photobucket.com/albums/oo58/milwaukeemidget/Midget%20Build/DSC_0387.jpg) (http://s361.photobucket.com/user/milwaukeemidget/media/Midget%20Build/DSC_0387.jpg.html)
2011 – making progress . . .
(http://i361.photobucket.com/albums/oo58/milwaukeemidget/Bonneville%202013/DSCN5327_zps0f679847.jpg) (http://s361.photobucket.com/user/milwaukeemidget/media/Bonneville%202013/DSCN5327_zps0f679847.jpg.html)
Albeit not without problems . . .
(http://i361.photobucket.com/albums/oo58/milwaukeemidget/970%20Spec/DSCN4530.jpg) (http://s361.photobucket.com/user/milwaukeemidget/media/970%20Spec/DSCN4530.jpg.html)
And in 2012, making the mistake of relying upon “getting advice and parts from well thought of suppliers” . . .
(http://i361.photobucket.com/albums/oo58/milwaukeemidget/DSCN4810.jpg) (http://s361.photobucket.com/user/milwaukeemidget/media/DSCN4810.jpg.html)
All leading to . . .
(http://i361.photobucket.com/albums/oo58/milwaukeemidget/Bonneville%202013/acd82b67-137d-4460-a08c-15cbe4f0fd2b_zpsbdb034ea.jpg) (http://s361.photobucket.com/user/milwaukeemidget/media/Bonneville%202013/acd82b67-137d-4460-a08c-15cbe4f0fd2b_zpsbdb034ea.jpg.html)
Honestly, I owe Fordboy a lot for taking the time to pull my head out of my deuterostome blastopore.
And yes, I will be going with a crank scraper. Can't afford a dry sump, but if there is any power to be gained with a scraper, I'm taking it.
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Reading through some racing magazines from the late 50s to early 60s, for info on a 61 Jag restoration, I found an article on a BMC 1100 cc Formula Junior engine that shows how much development Ford Boy and Chris have accomplished by taking a smaller engine further than the best engine builder of the time could. In 1962 85 horsepower and in 2012 it was 95 horsepower, IIRC.
Another article mentions the change in crankshaft harmonics when going to full counterweights bringing on crankshaft breakage.
Some engines of this period were using external oil pumps for pressurization and the stock internal pump for scavenging which means a low to no instance of cavitation. The only way to know is to test and measure the way it works, or does not.
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F1 motors always amaze me,
with the short pistons, rock over must be huge and he ring seal must be compromised.
If the ring seal is compromised, then lowered bhp must result. My guess is that the rock-over is well controlled and much less than you might imagine. In spite of the huge rpm's, the short stroke and relatively long con-rod length keeps the forces @ TDC overlap within reasonable limits.
I can see why such large scavenge pumps are used.
Not to mention the speeds these pieces of jewelry spin.
I had over the years started using scrapers on the cranks and screens to keep the oil away from the bottom.
The erosion on the impact side of the scrapers is impressive, these being fairly small motors and less than 10k revs. (intentional revs)
J
J,
See my note in your text.
:cheers:
F/B
FB, I agree with you
Take a look at the piston, very short skirt which you would think might not guide the piston through rock-over too well.
It would appear that there is a running surface? above the rings? Not what I call conventional, but it works.
Cheers, J
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FB, I agree with you
Take a look at the piston, very short skirt which you would think might not guide the piston through rock-over too well.
It would appear that there is a running surface? above the rings? Yes, it looks like the upper ring land was "touching" the cylinder wall. My experience is that this is OK as long as the cylinder wall surface is not "compromised" for ring sealing. It is a simple concept, difficult to "perfect". A different way to consider piston skirt length is to calculate the piston skirt area, (perhaps including top land area?), as a percentage of the "bore bearing area", (piston bearing area * the stroke length). The immediate possibility is that very short stroke lengths would allow very short piston skirt lengths (bearing areas) while still providing adequate stabilization, and reduced drag. I see LOTS of development time here.
Not what I call conventional, but it works.
Cheers, J
J,
What else I noticed in the photo:
A/ "Only" 2 rings for reduced drag
B/ rings are very narrow, maybe .5mm compression, 1mm oil control? Probably very low radial tension as well.
C/ Notice that the oil control drillings in the piston skirt, are partially below the ring groove. This enhances pressure differential driven oil control.
D/ "inboard" pin bosses, shorten pin length and therefore weight.
E/ Vertical stiffening ribs between piston skirt and the bottom of the ring lands.
F/ Titanium (?) con-rod.
G/ Con-rod bolts appear large for the big end diameter. A dead giveaway that the assembly is turning huge rpm's, as larger fasteners are required to resist the loads at
very high rpm's.
H/ Even though the con-rod is Ti, LOTS of strategic machining to reduce the mass of the con-rod.
I/ Based on the strategic machining, it doesn't appear that they are too concerned about "streamlining" the rod shape to reduce "rotational windage". These engines
undoubtably have very high negative pressures inside the engines.
:cheers:
F/B
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Is cavitation in the feed side oil pump a problem on wet sump engines with a lot of crankcase vacuum? It seems cavitation might happen before the desired oil pressure is obtained.
If you're pulling a vacuum on a sealed wet sump motor, the oil pump is pumping from a lower pressure to the same lower pressure at the bearings. I can't see how it knows any difference. Relative pump pressure should remain the same. Your gauge will read lower because it will be comparing the lower absolute pump pressure to outside ambient pressure. For example, if your pump will pump 60psi normally, and now you're pulling a negative 5psi on your crankcase, your pump will be pumping from -5 psi, but since the entire crankcase is at -5psi, it will just put out 55psi gauge (still a difference of 60psi). Shouldn't be a problem. Dry sump may be a different situation because you have a separate scavenge pump which, if pumping into an external tank vented to the atmosphere, will have to overcome the vacuum to return the oil to the tank, at least on motorcycle systems.
The challenge that the oil pump has when pumping from a reservoir (oil pan) is that there is only 14.7 psi available in the very best of cases plus any possible additional pressure that may be created by having the pump below the highest level of the oil and in most wet sump engines the pump is located above the oil level so there is nothing but the internal pressure in the engine case to make the oil go to the pump inlet. So with this 14.7 psi you have to over come the resistance through any kind of inlet strainer, flow resistance from the tubing that takes the oil from the inlet in the pan up to the pump inlet and also pressure to actually raise the oil to the pump inlet. Now if you very carefully measured what these pressure drops were they would be pretty small but you only have the, at best, 14.7 psi to over come them and then you need enough pressure remaining to actually get the oil into the open chamber that is made by the rotating teeth of a gear pump, of vanes of a vane pump or pistons of a piston pump. And you have to fill this volume fast enough so that the pressure (negative pressure in this case, vacuum) does not get so high that it draws the entrapped and dissolved air that is in the oil to "pop" out of the oil in the form of a bubble that will have to be recompressed along with the oil. That "pop" that you hear is cavitation and it can and will destroy pumps. Gear pumps are pretty resilient to cavitation, vane and pistons pumps can be destroyed in seconds from cavitation. So if you reduce case pressure you can certainly cause the oil pump to cavitate. Pumps are great at making pressure, fracking pump can pump a 50/50 mixture of water and sand to 15,000 psi, but they don't suck for $hit.
Rex
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Just a reminder that the goal of this experiment doesn't concern the making of power- rather, it is to attain better oil control, mainly less aeration. This particular engine (DOHC) will have the potential for much improvement in this regard, compared with the V8 I ran (pushrod), due to keeping all of the top-end oil drainback away from the crankcase (a separately scavenged chamber will collect all top-end drainback oil- cam bearings, followers, etc). The only "free" oil in the crankcase proper will be that which emanates from the rod/main bearings. Therefore, this is the perfect opportunity to also evaluate reducing the aeration created by the counterweights.
Hmm... I wonder if, a few years from now, I'll be trying to study how much aeration originates in the top end- cam followers, valve springs, etc.... :|
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Jack,
A separated (and sealed from the crankcase) "cam box/head area" is definitely the way to go, IMHO. Oil that doesn't return to the crankcase can't rain down on the spinning crank assembly. You will need a separate, appropriately sized, scavenge stage for this area, and a collection area for the oil. A coarse screen in the "collection area" prevents the scavenge pump from ingesting "debris", in the event of a failure/breakage. It can save an expensive pump from damage.
:cheers:
Fordboy
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Jack- Kevin Johnson of Ishihara-Johnson crank scrapers ( www.crank-scrapers.com ) which MM is talking to about a scraper for his Midget, has done a lot of work and research about windage and associated issues which are the subject of this thread. I think you have said you will be using some sort of scraper/windage tray arrangement. You might talk to him about it and see what he thinks with your specific special circumstance.
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Jack- thanks. Looks like a useful site.
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Many years ago I polished a crank, rods, etc. to reduce windage. The theory was that less oil would adhere to the shiny surfaces and there would be less windage. It was a lot of effort. Does anyone know about a scientific type comparison they verifies if this practice works?
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Googling for "Oil Aeration in an Internal Combustion Engine" turns up some interesting things, the first 3 are from MIT and the next couple are from SAE. Also there's a "Circle Track" (the magazine) article on windage and oil pan design http://www.circletrack.com/techarticles/ctrp_0603_oil_pan_design_windage_tech/viewall.html (http://www.circletrack.com/techarticles/ctrp_0603_oil_pan_design_windage_tech/viewall.html)
This one looks interesting http://gasturbinespower.asmedigitalcollection.asme.org/mobile/article.aspx?articleid=1424669 (http://gasturbinespower.asmedigitalcollection.asme.org/mobile/article.aspx?articleid=1424669)
Maybe there's something in those. I *think* you may have to pay to see the SAE & ASME papers
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I apologize for not titling this thread "Reduction of oil aeration". I didn't realize that the term 'windage' specifically refers to power loss.
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Well, yes -- but more often "windage" refers to the drift of a projectile due to (cross)winds.
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The late Grumpy Jenkins wrote in his book "The Chevrolet Racing Engine" that he built a plexiglass screen into an oil pan and used a dye (I think) in the oil and filmed the rotating assembly with a special high speed camera.
What he saw was that the oil hangs together like a rope wrapped around the crankshaft.
There's detail on all the other weird stuff that goes on inside the pan.
Page 119 if you have his book.
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I think the link to the Ishihara-Johnson has been posted before on this thread, but this one is specifically their tech page:
http://www.crank-scrapers.com/What%20is%20a%20crank-scraper.html
The whole concept, presented clearly and concisely. AND, the reasons why the crank will NOT "throw off" all the oil, even at very high rpm.
There is also a link to a 2010 European engineering paper on the subject:
http://www.ilasseurope.org/ICLASS/ilass2010/FILES/FULL_PAPERS/097.pdf
There is no charge to download this pdf. It's a 12 page article filled with "esoteric engineering speak". If you persevere there is good info in the article. I doubt very much though, whether any racer cares about average "particle size".
:cheers:
Fordboy
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That's some interesting reading.
Thanks Fordboy. :cheers:
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I bookmarked the Ricardo paper- thanks. I've read very little of Sir Harry's stuff- guess I really should, though.
Oops- I see that the paper was from 2010, and from the Ricardo Laboratory, not actually authored by the late Sir Harry.
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I bookmarked the Ricardo paper- thanks. I've read very little of Sir Harry's stuff- guess I really should, though.
Oops- I see that the paper was from 2010, and from the Ricardo Laboratory, not actually authored by the late Sir Harry.
1./ The High Speed Internal Combustion Engine, Sir Harry Ricardo, 1953 (420 pages) is always in the top 5 of my recommended reading list for those who wish to get into the engineering end of engines. It is however, hopelessly out of date regarding materials, designs, etc. BUT, Sir Harry can show you how to think differently about effects. IMHO, it is a worthwhile read for that.
2/ Design and Tuning of Competition Engines, Philip H. Smith, 1971 (468 pages) is another worthwhile read. Again dated, but strong on the basics.
3/ IC Engine Combustion, Fuels, Materials, Design, C.F. Taylor, 1985 (783 pages) A classic. Standard of collegiate texts.
4/ IC Engine Thermodynamics, Flow, Performance, C.F. Taylor, 1992 (574 pages) The companion volume to #3.
5/ Climax in Coventry, Walter Hassan, 1975 (158 pages) Covers the Coventry Climax engines of the 50's & 60's. And lays out the foundation of the relationships in
the British Racing Engine Industry of the period.
There are many more contemporary volumes now in print, that are far more modern regarding materials and design. Too many to list actually. These are the basics I recommend, and you can go anywhere from here.
:cheers:
Fordboy
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The challenge that the oil pump has when pumping from a reservoir (oil pan) is that there is only 14.7 psi available in the very best of cases plus any possible additional pressure that may be created by having the pump below the highest level of the oil and in most wet sump engines the pump is located above the oil level so there is nothing but the internal pressure in the engine case to make the oil go to the pump inlet. So with this 14.7 psi you have to over come the resistance through any kind of inlet strainer, flow resistance from the tubing that takes the oil from the inlet in the pan up to the pump inlet and also pressure to actually raise the oil to the pump inlet. Now if you very carefully measured what these pressure drops were they would be pretty small but you only have the, at best, 14.7 psi to over come them and then you need enough pressure remaining to actually get the oil into the open chamber that is made by the rotating teeth of a gear pump, of vanes of a vane pump or pistons of a piston pump. And you have to fill this volume fast enough so that the pressure (negative pressure in this case, vacuum) does not get so high that it draws the entrapped and dissolved air that is in the oil to "pop" out of the oil in the form of a bubble that will have to be recompressed along with the oil. That "pop" that you hear is cavitation and it can and will destroy pumps. Gear pumps are pretty resilient to cavitation, vane and pistons pumps can be destroyed in seconds from cavitation. So if you reduce case pressure you can certainly cause the oil pump to cavitate. Pumps are great at making pressure, fracking pump can pump a 50/50 mixture of water and sand to 15,000 psi, but they don't suck for $hit.
Rex
Rex,
Then I should be in trouble. The scavenge oil pump in my BSA is about 6" above the oil level in the sump and I am pulling a vacuum of about 5" H2O on my case. The pump shouldn't work????????? Could I also assume that my oil pump wouldn't work at all in a complete vacuum, being that it is higher than the oil level? I'm not a pump expert like you, but once the pump is primed (gear pump), and even though it loses its prime at times because it pumps more than the supply side, it seems to keep on working. And about the dissolved air in the oil; if the case is only at say 10 psi absolute, wouldn't the entrained air bubble phenomena be relative and therefore cause no more problems than if the case were at 14.7 (or 12.7 at Bonneville)?
Tom
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Tom, your pump works because it can develop more negative pressure (vacuum) than the 5 inches of H20 that your case is at and that is sufficient to draw the oil into the pump for it to operate satisfactorily. Now if you drew your case down to lets say -25 inches of mercury then it wouldn't work at all. And yes you are correct regarding the entrapped and dissolved air in the oil, as the case pressure drops and the oil temp increases this air is more rapidly removed from the oil due to the reduced surface tension of the oil due to the temperature and the differential pressure between the oil bubble and the case atmosphere.
I worked in the oil pump business for so long and good inlet conditions were so important for the life and performance of pumps that I prefer as much positive pressure on the inlet as possible and am always concerned when it is reduced.
Rex
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Rex,
Now to get back to Wobbly Walrus and his question about pulling a vacuum on a wet sump motor. Firstly, the wet sump motor would have to be sealed before he could pull a vaccum, i.e. no open vents. Then, if he uses another pump to pull a vacuum, the relative pressure difference within his motor between his oil level and his pump pickup would still require the same negative 1/4 psi (or whatever difference he must overcome in oil levels), and his pump should work fine. What would increase the tendency of his pump to cavitate in a partial vacuum?
Also please realize that in the above example of my BSA, I have a dry sump motor which is scavenging oil to a tank that is vented to the atmosphere, so you are correct that if I pull too large a vacuum, the scavenge pump will have to pump from a negative pressure against atmospheric pressure which creates a larger differential. Not so in a wet sump motor.
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It depends on where the majority of the hydraulic power losses occur. Pushing oil through long passages and orifi creates quite a bit of energy loss due to internal and external friction within the oil. This is not compensated by the lower pressure environment at the end of the system.
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It depends on where the majority of the hydraulic power losses occur. Pushing oil through long passages and orifi creates quite a bit of energy loss due to internal and external friction within the oil. This is not compensated by the lower pressure environment at the end of the system.
Bo,
I'm going to agree with you that it's going to take a certain amount of pressure to force the oil thru plain bearings and small passages, but having a lower overall absolute pressure should help this as well. The lower absolute pressure would help "suck!" Also, my opinion is that you're probably not going to get much vacuum with any system you install, or you're start sucking air in thru oil seals and gaskets. Lord knows how little oil pressure it takes for oil to leak out of British seals and gaskets! (3 inches of oil pressure is like 1/10 of a psi) A substantial vacuum, like -5 psi in internal pressure, which is about 120" H2O, should not affect the ability of a good oil pump to maintain sufficient oil pressure in a wet sump situation. I could be all wet on this one, but I'm sure someone else will correct me if I'm wrong. It's the best way to learn!
Tom
P.S. I can almost hear Rex pondering this one. And I should apologize to Jack for hi-"jacking" his thread.
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This discussion is getting to mental for this bike jockey. The answer is lurking somewhere in books about aircraft piston engine mechanics. They deal with more extreme situations than most everyone else.
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It depends on where the majority of the hydraulic power losses occur. Pushing oil through long passages and orifi creates quite a bit of energy loss due to internal and external friction within the oil. This is not compensated by the lower pressure environment at the end of the system.
Bo,
I'm going to agree with you that it's going to take a certain amount of pressure to force the oil thru plain bearings and small passages, but having a lower overall absolute pressure should help this as well. The lower absolute pressure would help "suck!" Also, my opinion is that you're probably not going to get much vacuum with any system you install, or you're start sucking air in thru oil seals and gaskets. Lord knows how little oil pressure it takes for oil to leak out of British seals and gaskets! (3 inches of oil pressure is like 1/10 of a psi) A substantial vacuum, like -5 psi in internal pressure, which is about 120" H2O, should not affect the ability of a good oil pump to maintain sufficient oil pressure in a wet sump situation. I could be all wet on this one, but I'm sure someone else will correct me if I'm wrong. It's the best way to learn!
Tom
P.S. I can almost hear Rex pondering this one. And I should apologize to Jack for hi-"jacking" his thread.
You will find that when you have "negative" pressure in the crankcase, any crankcase lip-seals will be facing the wrong direction. You can "flip" the seals around, but a better choice is "double lip seals", IF, any fit your application.
BTW, any pump is just a "differential pressure device". That is to say, if a pump has the ability to produce 60# of differential pressure, if the inlet pressure is zero, the outlet pressure should be 60#. But if the inlet pressure is say -15#, then the outlet pressure will be 45#. I have seen this many times when an oil pump has a restricted inlet from a too small a line size. Changing the line to the proper size magically produces higher pump outlet pressure, with no other changes. Lines need to be sized for the coldest operating temperature.
Rex, please correct me here if I'm in the wrong.
:cheers:
Fordboy
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Remember that you can only produce a -14.7 psi of vacuum so if the pump inlet was at -15psi it would not pump. I have seen pumps that will actually pump with as low as -24 inches of Hg before they cavitate but most of the gear pumps, vane pumps, gerotor pumps that are typical for engine oil pumps will start to cavitate at around -10 to -12 inches of Hg, and this would be under "perfect" test conditions, proper viscosity oil and temp. If you have a pump that picks up output volume when you increase the inlet size then it is cavitating with the small inlet.
Rex
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I'm guessing that means that oil pumps will not work in outer space? Not that my motor would actually run there either, so I guess it's a moot point.
Rex, I have a question for you in regards to the F-1 cutaway motor above. It appears that the crankcase pump is adjacent to the crankcase, although I'm not sure from the photo. Is there a separate pump that pumps oil from the sump back to the oil tank? And then, is there a 3rd pump that delivers oil to the bearings, etc.?
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Tom,
As I understand the F1 set up it has separate scavenger pumps for each "chamber" of the V8 engine, a chamber consists of the crank throw with two rod/piston assemblies, and each chamber is sealed from the one(s) next to it. They also have scavenger sections that draw oil from places like the cam towers also. The type of scavenger pump that they use is more like a small roots two lope blower which has a larger displacement that a comparable width gear pump and much better a drawing a vacuum in the case. As the oil in each chamber it really in the form of an aerated mist this type of pump is very effective. These pumps then return the oil and air to the tank, or possibly a "air/oil separater" then back to the tank to be picked up by the main pressure pump to be sent back to the engine. They also have additional pressure pumps for other functions such as running all of the hydraulic servos that control the shifting, clutch, brakes, and throttle to name a few.
Rex
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Rex,
I thought I was looking at a centrifugal air/oil separator on the end of the scavenge pump.
Dailey Eng builds some like this. I have an older modified Barnes pump with separator, trying to find another.
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I hadn't seen that- I like the idea of the centrifugal separator on the scavenge sections of the pump.
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Cosworth DFV (DFW, DFX, DFY, DFL) oil pumps have used a centrifugal separator section since 1968 I think.
:cheers:
Fordboy
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The oil that Toyota recommends for my truck is 0-20W synthetic. It seems that thin oil gives a lot of advantages as per windage. Do they run thinner oils in the F-1 engines? It seems it would drain down a lot faster and pump easier.
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Dry sump is cheaper than a another entry fee and a trip out from Beerhaven and another year with out the record trophy!
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Anybody here have experience running a Roots-type oil pump? Can someone direct me to an interior view of a centrifugal oil separator? I couldn't find anything on Dailey's website- other than an interesting video comparing scavenge-oil frothing with/without separator usage.
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I have run pumps with lobe scavenge in them Jack. No different in hook up or drive system, just more vacuum.
The best picture I have of a air-oil separator.
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A couple F1 dry sump pans & a new scavenge lobe design, Similar to current supercharger technology trends.
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That pan look similar to some recent cup pans I have seen. I wonder how they equalize the pressure between the cylinders? Mike do you have a picture showing the inside of the pan? Tony
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As I understand, to make these vacuum pumps work well they actually put a bleed orifice from atmosphere into the chamber that is being evacuated to allow a very small amount of air flow through the chamber. This flow prevents the vacuum pump from stalling which is a condition where it actually is not pumping anything and can lead to pump surge as air or combustion gases etc are leaked into the chamber and then the pump will evacuate them and then stall again, this can happen at fairly high cycle rate. At stall the power required to drive the pump drops as it is not doing any work. By adding a bleed orifice this is prevented and the vacuum level in the chamber is controlled.
Rex
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Rex,
Out of curiosity, I wonder if these bleed orifices have check valves to control the vacuum at which they bleed. I'm thinking that if the orifice is too large and not controlled, the pump might just pull in air and not pump oil. Analogy would be a two stroke motor with bad crank seals - - it won't start because the upstroke of the piston (vacuum pump) pulls in air thru the seals instead of fuel thru the carb. At high RPM where the pump is more efficient, the opposite might happen and the orifice might not be sufficient to prevent "stalling."
I wonder how many hours/dollars went into getting that right!
Tom
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That motor looks like a V6 to me.
Irrelevant, but I'm just saying.
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That motor looks like a V6 to me.
Irrelevant, but I'm just saying.
The oilsump housing pic looks like the old V10
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... This volume deal also makes it sound like Jack Giffords block arrangement could be an interesting advantage compared to typical 4-cylinder engines...
... I agree. I considered blocking off the unused cylinders, but quickly decided that additional crankcase volume is preferable, if for no other reason than reducing the magnitude of pressure fluctuations in the crankcase...
I just discovered another advantage (having it on the engine stand in its eventual position made it more obvious): I won't need to include a kick-out on the oil pan, since the [empty] unused cylinder volume will serve that purpose quite nicely! :-)
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I'm c-r-e-e-p-i-n-g up on making a little progress toward the full-circle counterweight scheme. Having the new billet crank in-hand has allowed me to make cardboard mockups of the planned magnesium alloy filler segments, to more easily visualize machining operations (on segments and on crank counterweights). And I'm finally corresponding with the right person at Elektron for full specifications and material quotes of their Elektron-43 alloy- about 43ksi tensile strength, but pricey! The modulus-of-elasticity isn't as good as I had hoped, so I've got to get more precise with the deformation calculations.
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Jack, how does the coefficient of expansion due to temperature change compare between the billet crank and counterweight materials? Will just warming up cause the circular weights to get loose from the crank?
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Thermal coefficient of expansion of Elektron-43 is 25.6 x 10^(-6). I still need to do all the engineering of the attachment scheme- might not be able to solve all aspects.
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Jack, if thermal expansion becomes an issue consider titanium. Its thermal expansion coefficient is less than iron or steel. It will tighten up onto the crank when it gets hot.
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... Thermal coefficient of expansion of Elektron-43 is 25.6 x 10^(-6)...
Oops! That seemed awfully high to me- about twice that of aluminum alloys. Looking back at the spec sheet, I now notice that number was per degree Kelvin, not Fahrenheit. So, per degree Fahrenheit it's more reasonable- about 14.2 x 10^(-6).
I also made an error converting gPA pressure units to KSI- so the elastic modulus isn't nearly as bad as I thought.
[At this rate, would you trust me to do any calculations?] :roll:
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Sure. When I read stuff like that , my eyes glaze over. :-D :-D
Ron
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Calculation and formulas make you think but most of the time some trial and error in LSR seems to rule. Observation of what works is also a plus. NHRA Pro-Stocks have 5 stage pumps AND a vacuum pump and the engine lives @ 10K + rpm even tho it is only for a short time.
I have run a vacuum pump on my inline 6's for 15+ years (maybe the first one) and until I redesiged the pan I saw minimal but still positive results. A ledendary pan builder (retired) helped me by showing what worked at the RPM I was running. That it one of the keys to all calculations. I would never run without a pump and a way to monitor it. Some engines can only flow so much air especially NA on gas at Bonneville and this must be considered also.....good luck