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Author Topic: Crankcase Exhaust Extractor  (Read 13352 times)
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Koncretekid
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« on: February 10, 2013, 09:29:26 AM »

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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saltwheels262
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« Reply #1 on: February 10, 2013, 09:46:02 AM »

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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saltwheels262
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« Reply #2 on: February 10, 2013, 10:15:44 AM »

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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bub '07 - 140.293 a/pg   120" crate street mill  
bub '10 - 158.100  sweetooth gear
lta  7/11 -163.389  7/17/11; 3 run avg.-162.450
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lta 8/14  - 169.xxx. w/sw2           
'16 -- 0 runs ; 0 events -- made a 2 state change in ZIP codes

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bak189
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« Reply #3 on: February 10, 2013, 11:03:16 AM »

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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« Reply #4 on: February 10, 2013, 11:09:45 AM »

http://www.et-performance.com/
I used this and was very impressed. It's a reed valve, I think.
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Dean Los Angeles
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« Reply #5 on: February 10, 2013, 01:39:25 PM »

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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« Reply #6 on: February 10, 2013, 03:16:31 PM »

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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Buickguy3
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« Reply #7 on: February 10, 2013, 07:05:29 PM »

   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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« Reply #8 on: February 10, 2013, 08:00:49 PM »

   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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« Reply #9 on: February 10, 2013, 10:20:26 PM »

   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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« Reply #10 on: February 10, 2013, 10:26:44 PM »

  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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Koncretekid
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« Reply #11 on: February 11, 2013, 08:43:21 AM »

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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« Reply #12 on: February 11, 2013, 09:10:15 AM »

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
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« Reply #13 on: February 11, 2013, 10:14:32 AM »

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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« Reply #14 on: February 11, 2013, 01:33:22 PM »

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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