Landracing Forum
Tech Information => Technical Discussion => Topic started by: mrfab on August 30, 2010, 10:19:28 PM
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The engine I am going to be running in our lakester came out of an NHRA Super Comp dragster. It is a wet sump BBC, 565 inches and presently has a Moroso vacuum pump for crankcase scavenging. Anyone had any good or bad luck running one of these type systems? My main concern is that the pump can't keep up with the pressure on a (hopefully) long course run. Any help would be greatly appreciated.
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A great question.
Yrs truly is involved with a handful of Top Dragsters and Super Comp diggers and also an advisor (?) to a few current Landspeed racers with similar engine but with dry sump combinations.
My gut feeling is for Elmo /Maxton/Lorin/Texas mile/Mojave mile, no problem, but for the salt, more pan capacity or add an oil cooler to the system.
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I've been running one for over 14 years. First one was a converted "smog" pump like Stefs but I was to cheap to buy one of his at the time. Learned about them from econo dragster guys. Converted smog pump vanes don't like oil vapor a lot.
Moved to an Aerospace Industries model a few years back with success. With a wet sump system I doubt you would have any problem. The key to wet sump system is a really well designed pan which helps control oil getting to the top of your engine. I know of a few BBC's that have external oil return lines from their valve covers to the pan.
I have a vacuum gauge on the pan and can see 7" to 9"; I usually glance at it one or two times on a run if I can. A good dry sump system also pulls a vacuum and adding a pump to it just makes it better. I have heard that too much will pull oil off of bearings but I have not had this happen to me. I've found clear condensate water in the catch can after a run also. I help a friend with a Blown BBC and he has a dry sump and a vacuum pump and has run over 250 without oiling problems.
ProStockers all have dry sumps and pumps but only go a 1/4 mile so I don't compare what they do to us. Not sure on pump to engine speed you may need to make and adjusment in that area...........Good Luck
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Just remember on a wet sump engine you are reducing the pressure on the inlet to the oil pump and there is a minimum inlet pressure below which the pump will cavitate and pump air bubbles thru your engine. Keep the pan deep and plenty of oil around the pump inlet. On a dry sump engine the case pressure makes no difference to the pressure pump inlet so lowering engine case pressure large amounts will not damage the engine and will make hps.
Rex
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I've heard a lot of debate on this in the last few years. There seems to be a lot of debate about the windage losses vs. case vacuum vs. piston spray cooling vs. scavenge trays vs. sump shape. JM2c, it seems that properly shaped wet sumps are as effective at limiting windage loss as dry sumps in straight line applications. I have a significant disagreement with a top engine builder about the windage loss vs. piston cooling issue.
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However there is no debate as to whether or not NASCAR is trying to develop every last HP they can find (ceramic cylinder liners anyone?) on an around the clock basis. They now make a reliable 930HP and there drysumps pull 20" of vacuum and require a relief valve in the valley to limit it so cyld. walls don't run dry. They don't run a vacuum pump but do run 6 stage oil pumps. There system address' windage, piston spray cooling and just about anything else you can think of. They are limited to 14 to 1 comp ratio and use a 830 cfm Holley carb. 2.6 HP per C.I. with an endurance engine. Do what there doing and you won't be to far off.
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OK, I'll come down on the side of sucking and spraying. Several engine builders I know disagree. Certainly dry sumps with pickups on all four corners are needed for road courses. Aerobatic aircraft are worse off and could benefit from road course experience.
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I run piston squirters, EDM rods, 5 stage dry sump, on a 565 that we shift at 8200 and have turned 7850 out the back ---I feel I am on the ragged edge---as we keep blowing up stuff we address that problem--working on eng plates and fly wheels now
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NASCAR engine builder are following the F1 engine builders in dividing the V8 engine into 4 separate compartments each with its own very large, and specially designed, scavenger pump to get the case pressure very low and this has a major affect on the windage in each section. F1 has been doing this for years and since a number of F1 engine people are now with NASCAR teams they have brought this technology with them. Lower pressure makes for less density and therefore lower windage drag which makes for more horse power.
As a note on windage reduction large power generation stations use hydrogen inside the generators to reduce windage and increase the efficiency of the generator. Try that with an engine.
Rex
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Rex, You are giving all the secrets away. :-o On my XO-GMC, I am running a six stage pump with 5 scavenge sections for this exact reason. As Rex mentioned the pan also has to be deigned to wok in conjunction. Tony
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You might want to touch base with Peterson Fluids Systems.
They have some tech info and frequently asked questions pages on their web site, and are very helpful folks.
http://www.petersonfluidsys.com/
They are doing active research in new pump designs and supply systems to some of the top race teams in the business including NASCAR,
Larry
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Thanks for all the help guys. I'll take a look at the pan real close and make sure it will do what it is supposed to. I'm thinking of doing a lug curve on the dyno and hold it at 6500 for a minute or so and verify that the pump is keeping up. Thanks again for all the input.
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Every Power Plant I have ever worked at used hydrogen as part of the cooling system for their large generators. For maintenance the H2 is displaced by CO2 and the CO2 is diplaced by air prior to opening...Been part of my electricians job for over 43 years. There are also either horizonal or vertical coolers inside the generators using tubing like a heat exchanger; bearing cooling water is the medium. The addition of higher pressure will allow more megawatts to be attained. Normally the boiler is the limiting factor.
I've serviced generators with as low as 5 psi (1945) to 60 psi.............................JD
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Has anyone heard of the oil being drawn out and problems with the piston pins due to high crank case vacuum?
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I think that would only be a problem if vacuum was higher than oil pressure.
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Yes on the piston pins ---that is why I have EDM drilled rods
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Yes on the piston pins ---that is why I have EDM drilled rods
How high was the vacuum when you had trouble before you oiled the rods?
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Oiling of con rods (those with chamfered oil holes in the small end) and piston rings is mostly by oil spray lofted up into the cylinder off of the con rods side clearance. Much of that oil spray is distributed by the air turbulence in the crank case and cylinders as the pistons go up and down. Once you evacuate the crank case to about 11 inches of vacuum the air pumping of the bottom end is drastically reduced so the oil thrown off the rod big end side clearance mostly just goes on a straight line until it runs into something instead of getting churned around by air motion.
Crankcase vacuum also increases the relative pressure of the oil system as it is no longer fighting crank case pressure to escape from the big end bearings side clearance so oil loss through the side clearance tends to increase.
In marginal oil systems that can lead too much oil leaving the big end but it is not getting to the usual places due to lack of air turbulence stirring it around.
As mentioned above your oil pump also now is pulling oil up the pickup tube against the higher suction required due to the lower pressure in the oil pan (in an engine without a vacuum pump crank pressure is often above atmospheric pressure) which would help the oil pump pull oil out of the crank case. Once you start using an evacuated crankcase that assistance provided by blow-by pressurization of the crank case disappears.
The solutions used include diamond hard coated wrist pins and pressure oiled small ends on rifle drilled rods or oil squirters in the crank case to spray oil directly on the wrist pins and piston crowns to both cool and oil them.
Larry
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Well said Larry! I agree completely. Adding a vacuum pump to a drag motor is one thing but to an endurance motor is a different "kettle of fish". (and any engine that has to run WFO for five miles is an endurance engine in my book!) As Larry has said you need to pay attention to getting lube to the required places and things like DLC (Diamond like coatings) are needed. Again F1 engine development leads the way in developing engines that can live with large amounts of case vacuum. They are running some engines with the con rod directly against the wrist pin using DLC.
Rex
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"I have EDM drilled rods"--
I do not know what we are pulling vacum wise.
When we went to dry sump after hurting two cranks at b'vill the EDM rods were just part of the package from the eng builders experience with BBC boat motors with dry sumps and vacum pumps.
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agreed,
we experimented with a hard / dry film coating of the wrist pins back in 1987.
the other option is a ceramic flash coating which is commonplace today.
caution that some of these will wear a common spirolock into nothing.
some of the dry sump suction side locations on the valve spring cover will make the enxt closest rocker and spring not have oil.
a simple baffelplate will help quite a bit.
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Valve spring oilers have dramatically changed our valve spring life---we went to piston squirters trying to help control piston crown temps primarilly we probalay loose most of the HP gains by putting much more windage oil in play.
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Valve spring oilers have dramatically changed our valve spring life---we went to piston squirters trying to help control piston crown temps primarilly we probalay loose most of the HP gains by putting much more windage oil in play.
Yea, but I think your better off!
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Hey all
I'm gunna run a weslake 500 speedway engine . It is designed to be a total loss oil system--The oil just falls out on the track or
into a container
The bottom end is a combination of needle rollers (bigend) balls & roller (mains)
The oil exits through 2 flapper valves operated by crankcase pressure.
I have turned the engine from verticle to about 30deg so the outlet holes are not at the bottom.
Would one of these vacuume pumps cope with moving about 1 qt of oil in a run.
I like the electric idea as I wouldn't have to make a drive system fo the pump.
cheers Bones
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RP harley guys have a small electric pump they run on the salt
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more pan capacity
Yup. With such big displacement, and the original case volume, the pressure spikes just from piston motion is high. More volume, anywhere it can be hidden, is better, but it's got to be connected directly to the pan/case space (not the valve covers).
Re: pump inlet pressure vs. case vacuum.
By definition, a vacuum system is not vented to ambient. The entire hydraulic system (suction, bypass relief valve, and bearing/tappet/rocker leakage) is vented to the same pressure: the case. The differential between suction and pressure is the same regardless of the starting value.
However: even though the pump delivers exactly the same pressure and volume (but not on a gauge balanced to atmospheric pressure!), as Rex says, the small change in pressure is far more dangerous on the suction side.
Doesn't this suggest that the entire suction side (pick-up head, tube, passage in the pump body, low-press port) should be larger X-section as compensation?
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Larger cross section on the oil pump inlet certainly helps the pump inlet conditions along with minimum other restrictions, i.e. 90 deg fittings etc. but compared to having the engine case pressure down to 10 or 11 psia these "improvements" really won't do much to improve the pumps inlet conditions. Fortunately most oil pumps are either gear or geroler design which have pretty good suction characteristic but at these low level of inlet pressures they are probably very close to cavatation and probably are cavating in many situations. When the pump cavatates it will start to pump small air bubbles through the engine and as I remember air is not a good lubricant. I have never thought case vacuum pumps were a good idea for a wet sump engine.
Rex
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Rex,
We typically see about 40hp gains with our normally aspirated 750 hp small block engines.
I would hate to throw that away.
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There's an interesting idea on purging the pressure side back to the pan here: http://crank-scrapers.com/Chrysler_slant6_performance%20pump%20mod.html
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Robfrey,
There is one possible advantage that using a vacuum pump on a wet sump engine that I have never heard discussed and it may be that it is also why the low pressure on the oil pump inlet does not completely cavitate the oil pump to destruction and that is that a low case pressure and elevated oil temps, which reduce oil viscosity, the entrapped air that is in the oil is drawn off by the vacuum. This is very similar to a process, vacuum dehydration, that is used in many hydraulic systems to remove water. All oil has some level of entrapped and dissolved air in it and when the oil is wiped around by things like crank shafts and rods more air is entrapped, it is this air that when it is pulled out of the oil by a pump with a low inlet pressure causes cavitation. It could just be that the case vacuum reduces the amount of entrapped air to a level that reduces or prevents oil pump cavitation. I would require some testing to verify but it certainly has some merit.
Rex
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When I built my "Rube Goldberg" dry sump oil tank I was advised to put a sight glass on each side to check for oil bubbles---I went to great lenth to build a system of screens and slopes to make the oil run across surfaces that would "pop" the bubbles.
Later I removed the sight glasses when I determined that I never saw a buble.