Landracing Forum
Tech Information => Technical Discussion => Topic started by: Koncretekid on February 10, 2013, 09:29:26 AM
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In my idle time, I have thought about adding an exhaust extractor to try to pull a vacuum on my crankcases. Anyone familiar with single cylinder motors (or 360* twins) knows that they try to pump their cylinder capacity, 500cc in my case, in and out of the crankcase on every revolution, which wastes power. I've tried a PCV valve on the breather, but I don't think from what I've read that the PCV valve can oscillate fast enough to evacuate the motor at 9000 RPM's. A reed valve, such as sold by Colorado Norton Works is reputed to work much faster, but reports are that even they lose effectiveness at high RPM's. A sump evacuation pump may be possible but probably unwieldy on a small MC. So an exhaust extraction system, such as the Moroso 25900 (http://www.moroso.com/catalog/categorydisplay.asp?catcode=13023) seems to be a possible solution.
Questions:
1.) Is anyone currently using such a system on a motorcycle or other single cylinder motor?
2.) Moroso's installation instructions show the extractor tube slash cut and parallel with the exhaust flow. It just looks wrong to me. Also, I noticed that Summit (http://www.summitracing.com/search/brand/summit-racing/product-line/summit-racing-crankcase-evacuation-systems) sells an almost identical one, without the small birdmouth cut in the leading edge. So what's the deal?
3.) What would be best placement in a free flowing continuous header pipe that is say 1-7/8" by 23" long with a couple of 90* bends?
4.) Any suggestions on extractor pipe size to use?
I am prepared to experiment, but I would like to gather as much info as possible beforehand as I'll probably only get one shot at a dyno test, if any, before I run again.
Tom
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drag bikes used to run valve similar to those towards the end of their exhaust pipes.
the hose would lead to the crankcase.
you don't see too much of that anymore.
I don't know why.
bf
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I would try that crankcase evacuation system you are thinking of.
a valve on the exhaust pipe 6 to 8 inches from the open end.
the other end of the hose attached to an engine side cover or such on the lower end,
where there is not a lot of oil spray but, where crankcase pressure will be maximized.
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Having a lot of room on our LSR sidecar .......we used a vacuum pump as sold by Fast by Gast... used on drag bikes......never did run a Dyno-check with the pump in place and working.....so don't know how much it helped......................................
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http://www.et-performance.com/ (http://www.et-performance.com/)
I used this and was very impressed. It's a reed valve, I think.
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The Krank Vent system claims to "maintain a constant vacuum of -5 to -7 psi". That's not helpful on the up stroke. To be totally useful you would have to provide vacuum on the down stroke and pressure on the up stroke.
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I've never used one Tom so no help sorry, would be keen to see back to back dyno runs with and without from someone other than the people selling them.
Only reason I posted is if your running on a Dyno make sure the O2 sensor is a fair way upstream of it or it will mess up your readings.
Cheers
jon
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Those valves that Summit and Moroso sell are copys of the old OEM smog pump check valves. We used to go to the junkyard and use them on our drag car. I guess the principle hasn't changed much over the years. That was 35 years ago.
Doug :cheers: :cheers: :cheers:
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Those valves that Summit and Moroso sell are copys of the old OEM smog pump check valves. We used to go to the junkyard and use them on our drag car. I guess the principle hasn't changed much over the years. That was 35 years ago.
Doug :cheers: :cheers: :cheers:
Here too, I just welded one of those valves onto a piece of pipe and used a smog insert from a car with air injection......no dyno comparison, makes enough vacuum to just about rip the end off your finger..... was at the suggestion of Jack Dolan.
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Those valves that Summit and Moroso sell are copys of the old OEM smog pump check valves. We used to go to the junkyard and use them on our drag car. I guess the principle hasn't changed much over the years. That was 35 years ago.
Doug :cheers: :cheers: :cheers:
Same here. I've had better luck with the wrecking yard ones than new ones. The used ones seemed to take less pressure to open but still close quickly.
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That's because the auto mfg's. had to guarantee them to function for 100,000 miles. [or replace 10 million of them]
Doug :cheers: :cheers: :cheers:
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My concern with any crank vent check valve, whether it be a PCV valve or a pollution control valve is that they appear to be a spring load disc, which I have heard more or less "floats" when the pulse reach 9000 RPM which is 150 pulses per second (even on a 4 stroke). I'm pretty sure the auto manufacturers were not concerned with them working at those RPM's, as I doubt that the environmental tests required that. The reed valve ones, made using reed valves designed to control intake pulses on 2 stroke engines are supposed to work at high RPM's. If they float or flutter at my max hp RPM, which is somewhere around 8300 RPM, none of them will help max hp. That is why I think the exhaust extractor would be superior, as I would think the venturi effect vacuum signal would continue to increase as the exhaust velocity increases. The check valve then only comes into effect on a backfire which might allow a flame front to travel backwards into the cases. If I can get the exhaust extractor to work, the check valve operation may become less important, as it may simply stay open until that backfire happens. I have no desire to experience the results of the "big bang" theory first hand!
The Krank Vent system claims to "maintain a constant vacuum of -5 to -7 psi". That's not helpful on the up stroke. To be totally useful you would have to provide vacuum on the down stroke and pressure on the up stroke.
Yes, we have that problem with reciprocating motors. A long cylinder with a piston at each end like a steam engine might work, but I'm sure someone has tried that. One way to mitigate the crankcase pressure problem is simply to make a large enough breather hole that the air can travel in and out with little resistance. Thinking a hole the size of my piston. Preferably the hole is there and the motor is still running!
Tom,
I once helped install the Moroso part you linked to on a turbo drag car. My understanding of the slash cut in the exhaust is that it helps to create a localized low pressure on that end of the extractor pipe from the exhaust stream passing over it. The pressure differential helps evacuate your crank case. I have seen home made media blasting set ups that use the same principle.
A reed valve might be a good solution on a bike due to space constraints. There are 2 stroke snowmobile engines that run up past 8000 RPM on reed valves. I would imagine that means you could source something that would keep up with a 9000 RPM 4 stroke.
It would be very interesting to see back to back dyno runs with and without the evacuation system in place.
Looking at the installation instructions for the Moroso unit, the slash cut end lies almost flush against the pipe wall. Can't see how that creates any pressure drop. The bird's beak opening is upstream, so my guess is the flow of the exhaust thru this small opening is what causes the lower pressure at the slash cut opening. But since the Summit Racing one doesn't seem to have this feature, I wonder if it's just another case of " smoke and mirrors". I'm going to try some different designs using a shop vac, some plastic "exhaust pipe", different extractor shapes, and a manometer to see if one way pulls more vacuum than another.
Tom
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Is there a way you can easily (?) record the crankcase pressure while the engine is running though the rpm range? Preferably on a dyno? Accurate measurements of crankcase pressure or (hopefully), vacuum are very useful. I'm thinking that for the rpm you need to run, a reed valve combined with a large check valve will be what is needed. You might want to use an airflow number which simulates your actual exhaust flow, for your manometer tests of extractor designs.
BTW: One of my clients has firsthand experience from a crankcase backfire..... It wasn't a good experience, as you fear.
:cheers:
Fordboy
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The way these units are suppose to function as crankcase exhaust extractor is as follows:
When the pressure is high in the exhaust pipe/collector the check valve is closed,,,
When the pressure is low in the pipe/collector then the check valve opens and crankcase fumes flow into the pipe/collector lower pressure,,,
The trick is that there is a BIG momentary pressure drop in the exhaust pipe/collector when an exhaust gas slug passes by any point in the exhaust pipe.....
Think of it as a "Pulse Pump"
Normal crankcase pressure of a "healthy" engine is about 2" of H20 above ambient pressure in a naturally aspired engine, and normal exhaust pipe pressures are constantly cycling positive and negative in psi with the cylinder pulses...
How effected this kind of system can be depends on several engine design factors to complicated to go into here....
Testing is to best way to see if there is any benefit or handicap...... but no on seems to take the time to do it,,,,or they keep quiet if they find some horsepower.....that's racing
Robert
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Mark,
So for my 500cc motor, if I have calculated correctly, my intake flow at 8000 RPM would be around 69ft^3/minute, but what would my exhaust flow be? I think the big shop vac will probably move 200ft^3/ minute, but it is hard to check.
Theoretically, I have just one breather on the B50 BSA so I should be able to measure crankcase pressure, assuming that I had the proper gauges, which I don't. I say theoretically because most BSA's have a bunch of unscheduled breather points. I have a manometer which will read up to 10" H2O, so I could hook that up. Unfortunately the motor is sitting on the floor, the frame is waiting to be painted on a warmer day probably next June, etc. etc. And the nearest dyno is about a 6 hour drive, but it is on the way to Loring, ME, so that will be the first chance I get to try anything new. So for now, it is just bench racing, trying to set up some things for the dyno run.
Having a lot of room on our LSR sidecar .......we used a vacuum pump as sold by Fast by Gast... used on drag bikes......never did run a Dyno-check with the pump in place and working.....so don't know how much it helped......................................
Bak,
I was wondering whether such a vacuum pump would affect the scavenge side of the oil pump? Some have said that it might reduce oil flow back to the oil tank (which is open to atmospheric pressure) which could result in wet sumping.
Tom
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Here is a theoretical question about crankcase pressure (or vacuum) that may be possible using only a check valve. If the total volume of the crankcase of my motor is 4 litres, and using .5 litre as the swept volume, it would seem that the upstroke of the piston would increase the volume by .5/4 =12.5%, which should decrease the absolute pressure by a similar amount (at a constant temperature) if it were sealed, such as by a check valve. Would this not result in a new absolute pressure of something like 12.9 psi, or a gauge pressure of - 1.8 psi? This would be almost 50" H2O. Of course, if we attach a gauge, it would only read the average pressure (vacuum) of .9 psi or 25" H2O. Is my reasoning correct?
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Mark,
So for my 500cc motor, if I have calculated correctly, my intake flow at 8000 RPM would be around 69ft^3/minute, but what would my exhaust flow be? I think the big shop vac will probably move 200ft^3/ minute, but it is hard to check.
Theoretically, I have just one breather on the B50 BSA so I should be able to measure crankcase pressure, assuming that I had the proper gauges, which I don't. I say theoretically because most BSA's have a bunch of unscheduled breather points. I have a manometer which will read up to 10" H2O, so I could hook that up. Unfortunately the motor is sitting on the floor, the frame is waiting to be painted on a warmer day probably next June, etc. etc. And the nearest dyno is about a 6 hour drive, but it is on the way to Loring, ME, so that will be the first chance I get to try anything new. So for now, it is just bench racing, trying to set up some things for the dyno run.
Tom
Tom,
Since you cannot duplicate the pressure in the exhaust pipe when the exhaust valve first opens at the blowdown period (pressures probably in excess of 100psi) without a 50/75 hp electric motor and a very large rotary vane blower, I would do the testing through the exhaust pipe with the shop vac wide open. I would then test angles & shapes of the insert (vacuum adaptor) for the highest depression. (vacuum extraction) Make a water manometer out of some vinyl tubing, a yardstick or tape measure and a wooden board to support everything.
The majority of dyno testing I have done uses calibrated gauges (in cfm) to measure & quantify whether the crankcase produces either blow-by (positive pressure) or vacuum (negative pressure). These are now done digitally, but originally were an analog measurement. If your dyno facility is not capable of measuring crankcase vacuum/pressure, a 5/10 cfm gauge (.5 cfm graduations minimum, .1 cfm is better) is cheap enough. (If they do not measure this, it shows that they are not serious about development.) You can then connect the gauge to your crankcase breather via Tygon or other clear, heat-resistant tubing. Your first efforts should be to minimize or eliminate, blow-by. Your engine should have a max. of 1.0 cfm blowby. More than this indicates either very poor ring sealing or excessive windage in the crankcase. A hot cylinder leakdown test can identify poor sealing of the rings, and often on bike engines this identifies poor cylinder wall prep and/or concentricity. If you can't get the rings to seal, you can never control crankcase pressure effectively, and, it is lost horsepower.
Have you ever done any hot leakdown checking to evaluate ring to cylinder wall, valve to seat sealing? If so what were the leakage rates? Hot leakage rates in excess of 1/2% (at TDC) indicate that those basic issues need to be corrected. BTW, thinking that excess leakage rates will "wear-in" is optomistic. It's like playing 5 card stud with 4 cards.........
Crankcase vacuum, on the other hand, presents opportunities for bhp gains. Less windage = more bhp. Crankcase vacuum allows the initial ring tension to be lowered (on all rings) reducing parasite drag for a free net bhp increase, as long as effective ring seal can be maintained. But do not be deceived, achieving higher levels of crankcase vacuum, and their attendant benefits, is a difficult process.
Access to a dyno that already has these test capabilities would be helpful. Let me know if you need more info on this.
:cheers:
Fordboy
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Regarding the issue of bore concentricity and ring sealing - this from a column by Robert Goldman, who was a friend of Al Moss', the founder of Moss Motors -
In classic bench racing mode -
"Al proceeded to claim he could bend an MG-T engine block with his bare hands. Suffice it to say, we group of experts immediately concluded such a thing was impossible. With his “bet” made, Al produced a bore micrometer, which he set lengthwise into the top of cylinder number two or three in a bare block. He then placed a towel under the block.
. . . Al interlaced the tips of his fingers, placed the heel of his palms on either side of the block, and squeezed. The micrometer fell out of the bore into the towel. Bet won." *
Yeah, I can hear the Pommy Car jokes already, but if a bare cast iron block can be bent a few thousandths at room temperature, what chance does an air cooled cast aluminum jug with an iron sleeve have at temp on the salt flats?
This is also a concern of mine in engines like the Flatcad, and any block which has large, unsupported areas.
I'm thinking that some blow by is just going to have to be accepted on this one.
* http://www.mossmotoring.com/a-life-well-lived/
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As Mark has suggested, I did some trials using a shop-vac (10.5 amp) to blow thru a 1-1/2" PVC pipe about 15" long, and measured vacuum using a manometer attached to different configurations of extractor tubes. Following are some photos and the results I got. It will take a few posts to get them all attached. Interestingly, the trial using a tube slash cut at 45* and with a small bird's beak cut into the upstream wall, and inserted into the pipe at a 45* angle as suggested by a reputable supplier, resulted in a poor vacuum reading. The best results were achieved by playing around with a tube extractor, pushing it further into the pipe, and then rotating it almost 90* to the pipe opening. With that set-up, I could get almost 5" H2O vacuum compared to 0.8" using the 45* insertion with the bird's beak.
Tom
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I made some drawings of the different trials, printed them, and then scanned them. It will take two posts to get them all in.
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The 4th and 5th page:
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I then got the bike back together and connected a tee to my breather, which is then connected to a simple PCV valve to attempt to reduce crankcase pressure. I was able to get almost 5" H2O vacuum at idle, which diminished to about 2" at 5000 RPM's, no load on the motor. I think a reed valve (the XS650 site has nice ones, but not in stock now.) will be more effective, as the PCV valve may not be able to react quickly enough to higher RPM's. Now if I connect the exit from the reed valve to the exhaust extractor, will I get the additive vacuum from the two added together?
Tom
P.S. In case you're wondering, yes, the B50 breathes thru the primary case.
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Simple principals, methodically tested, integrated into a positive result.
A lot of wags will run on, "Gee, is it worth all that time and effort?"
Yes, because NOW YOU KNOW what works best.
Look at the HUGE difference placement and shape have on the results!
:cheers: :cheers: :cheers:
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Tom,
pushing the piece that far into the exhaust pipe is going to change the tune on the motor.
wouldn't you think ?
bf
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Tom,
pushing the piece that far into the exhaust pipe is going to change the tune on the motor.
wouldn't you think ?
bf
Bill,
I had the same thought, but I won't know til I get it on the dyno, and have a way to insert it, then remove it to find out.
Simple principals, methodically tested, integrated into a positive result.
A lot of wags will run on, "Gee, is it worth all that time and effort?"
Yes, because NOW YOU KNOW what works best.
Look at the HUGE difference placement and shape have on the results!
:cheers: :cheers: :cheers:
In other words, you can't always believe what you read!
Tom
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Oh, Chris, how could you??
Principals are the people in charge of the school or the main participants in a business group (lawyers, for instance).
Principles are the steadfast rules - morals, if you will.
2 points off your total. Sorry. .. :evil:
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Oh, Chris, how could you??
Principals are the people in charge of the school or the main participants in a business group (lawyers, for instance).
Principles are the steadfast rules - morals, if you will.
2 points off your total. Sorry. .. :evil:
In this case, I am the principal.
My principle experience with principals is that they have no principles.
I hated high school.
But I salute this site’s upstanding principal’s principles, and acknowledge the fact that he has the most principal invested in this virtual principality.
It's just one of those words that are so seldom seen, slim is the chance that an error would be noticed.
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Hey -- you callin' me a chance? :?
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Fat is the chance you'll live this one down.
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GOOD ONE MM :-D :-D :-D :-D :-D
especially the sss-line 8-) 8-) 8-)
........After the 'chance' comeback.........Slim is at a loss for words :wink: :wink:
Great Thread, Tom :cheers: :cheers: :cheers: :cheers: