Author Topic: Crankcase Exhaust Extractor  (Read 20287 times)

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Offline Koncretekid

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Re: Crankcase Exhaust Extractor
« Reply #15 on: February 13, 2013, 06:57:54 AM »
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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Offline fordboy628

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Re: Crankcase Exhaust Extractor
« Reply #16 on: February 14, 2013, 04:25:52 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.

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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Offline Milwaukee Midget

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Re: Crankcase Exhaust Extractor
« Reply #17 on: February 14, 2013, 09:01:57 PM »
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/
« Last Edit: February 14, 2013, 09:05:31 PM by Milwaukee Midget »
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Offline Koncretekid

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Re: Crankcase Exhaust Extractor
« Reply #18 on: March 29, 2013, 02:59:25 PM »
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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Offline Koncretekid

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Re: Crankcase Exhaust Extractor
« Reply #19 on: March 29, 2013, 03:01:43 PM »
I made some drawings of the different trials, printed them, and then scanned them.  It will take two posts to get them all in.
We get too soon oldt, and too late schmart!
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Offline Koncretekid

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Re: Crankcase Exhaust Extractor
« Reply #20 on: March 29, 2013, 03:02:39 PM »
The 4th and 5th page:
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Offline Koncretekid

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Re: Crankcase Exhaust Extractor
« Reply #21 on: March 29, 2013, 03:10:16 PM »
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.  
We get too soon oldt, and too late schmart!
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Offline Milwaukee Midget

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Re: Crankcase Exhaust Extractor
« Reply #22 on: March 29, 2013, 04:12:50 PM »
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:
"Problems are almost always a sign of progress."  Harold Bettes
Well, I guess we're making a LOT of progress . . .  :roll:

Offline saltwheels262

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Re: Crankcase Exhaust Extractor
« Reply #23 on: March 29, 2013, 04:41:02 PM »
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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Offline Koncretekid

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Re: Crankcase Exhaust Extractor
« Reply #24 on: March 29, 2013, 07:54:23 PM »
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
We get too soon oldt, and too late schmart!
Life's uncertain - eat dessert first!

Offline Seldom Seen Slim

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Re: Crankcase Exhaust Extractor
« Reply #25 on: March 29, 2013, 08:52:47 PM »
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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 (that's way up north)
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Offline Milwaukee Midget

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Re: Crankcase Exhaust Extractor
« Reply #26 on: March 30, 2013, 12:34:46 AM »
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.
"Problems are almost always a sign of progress."  Harold Bettes
Well, I guess we're making a LOT of progress . . .  :roll:

Offline Seldom Seen Slim

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Re: Crankcase Exhaust Extractor
« Reply #27 on: March 30, 2013, 09:21:37 AM »
Hey -- you callin' me a chance? :?
Jon E. Wennerberg
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 (that's way up north)
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Offline Koncretekid

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Re: Crankcase Exhaust Extractor
« Reply #28 on: March 30, 2013, 10:15:00 AM »
Fat is the chance you'll live this one down.
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Offline Old Scrambler

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Re: Crankcase Exhaust Extractor
« Reply #29 on: March 30, 2013, 08:15:14 PM »
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:

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