gbyron you awake? CFM of 928 blow by gasses
06-16-2004, 02:40 AM
#31
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Andy,
Yeah, I'm (still) awake. I love classes where when I show up late, others do my math homework, thanks Lag (and everybody else)!
Had a treatise typed up this morning, but the site went down when I went to post. Oh well. Most of my points have been covered by others - esp all the gas law stuff and the crankcase venting to where issues.
As Old and New (and others) pointed out, each engine will be different in the amount of blowby for all the obvious reasons. Forced induction will add to the blowby.
Just don't overthink it. If you want to basically solve the blowby, get a decent estimate of what you think is blowing by. Source a vacuum pump that pulls enough for a decent cushion from some large-displacement domestic motor. Be done. You won't be 100% optimized, but unless it's a really close race, does it matter really if you leave one or two HP on the table?
Greg
Yeah, I'm (still) awake. I love classes where when I show up late, others do my math homework, thanks Lag (and everybody else)!
Had a treatise typed up this morning, but the site went down when I went to post. Oh well. Most of my points have been covered by others - esp all the gas law stuff and the crankcase venting to where issues.
As Old and New (and others) pointed out, each engine will be different in the amount of blowby for all the obvious reasons. Forced induction will add to the blowby.
Just don't overthink it. If you want to basically solve the blowby, get a decent estimate of what you think is blowing by. Source a vacuum pump that pulls enough for a decent cushion from some large-displacement domestic motor. Be done. You won't be 100% optimized, but unless it's a really close race, does it matter really if you leave one or two HP on the table?
Greg
06-16-2004, 03:55 AM
#32
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could you put the collector between the engine and the smog pump?
I like the smogpump Idea/ genius
Perhaps you can introduce a controlled air bleed before the separator to cool the vapors? This will also condense the water vapor, too.
Greg,
There is a fundamental problem with the math that Lag has offered in that there is more cfm of exhaust air than intake air. After all, this rapid expansion of intake air when ignited with gasoline, AKA combustion, is what makes the car go. The question is how much more exhaust air than intake air.
Thanks guys
06-16-2004, 01:16 PM
#33
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Andy,
The only way to *know* for any given car is to actaully measure it. There is no way to mathematically predict to a high degree of accuracy.
The cheap way out would be to build a box of around 55 gallon capacity. Utilizing some rather large hose so as to have no restrictions, attach one end of the tube to the oil filler in lieu of the cap. Remove the rest of the feeds from the oil filler to the intake and any other way the car may be ventign it's crankcase. The other end of the tube goes to to the bag - which is 'deflated' but in the box (I'm sure you see where this is going).
Drive car to dyno before actually attaching anything. Hook it up, do a couple of pulls, each time noting time and number of revs it takes to fill the bag to the volume of the box. (you should be able to get the exact number of ingition cycles during the pull off the dyno - or just multiply it out.)
Anyway, if you know the volume of the box and the amount of time that it takes to fill the plastic back in the box - then you can determine a CFM of blowby for your particular test subject that day at that altitude, mixture strength, boost, ignition timing, etc. That should get you more than close enough. Theres' still a bunch of stuff that will change from one car to the next, but the changes are really not worth worrying about.Other than maybe boost.
Gotta do it on a dyno. Numbers are different under load.
This is the 'ol-fashioned' way of doing exhaust volume measurement too.
If you're feeling really techie, do what they labs often do - use a hotwire sensor. Bu that'll be some $ unless you homebrew it.
Greg
The only way to *know* for any given car is to actaully measure it. There is no way to mathematically predict to a high degree of accuracy.
The cheap way out would be to build a box of around 55 gallon capacity. Utilizing some rather large hose so as to have no restrictions, attach one end of the tube to the oil filler in lieu of the cap. Remove the rest of the feeds from the oil filler to the intake and any other way the car may be ventign it's crankcase. The other end of the tube goes to to the bag - which is 'deflated' but in the box (I'm sure you see where this is going).
Drive car to dyno before actually attaching anything. Hook it up, do a couple of pulls, each time noting time and number of revs it takes to fill the bag to the volume of the box. (you should be able to get the exact number of ingition cycles during the pull off the dyno - or just multiply it out.)
Anyway, if you know the volume of the box and the amount of time that it takes to fill the plastic back in the box - then you can determine a CFM of blowby for your particular test subject that day at that altitude, mixture strength, boost, ignition timing, etc. That should get you more than close enough. Theres' still a bunch of stuff that will change from one car to the next, but the changes are really not worth worrying about.Other than maybe boost.
Gotta do it on a dyno. Numbers are different under load.
This is the 'ol-fashioned' way of doing exhaust volume measurement too.
If you're feeling really techie, do what they labs often do - use a hotwire sensor. Bu that'll be some $ unless you homebrew it.
Greg
06-16-2004, 07:39 PM
#34
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gotta go echo greg on this one: http://www.totalseal.com/gaplesss.html indicates a blowby of 20% or more w/conventional rings!! that's 4x what you are calculating for static blow by.... probably really should measure somehow and see what we're really pumping into electric car owner's lungs as we merrily whiz by...
http://www.autospeed.com/cms/article.html?&A=1576 has some interesting notes on can design...
http://www.superflow.com/support/sup...r.htm#blowbyyy has some ways to measure it accurately...
http://www.autospeed.com/cms/article.html?&A=1576 has some interesting notes on can design...
http://www.superflow.com/support/sup...r.htm#blowbyyy has some ways to measure it accurately...
06-17-2004, 02:42 AM
#36
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Andy,
If we both make it to OCIC, I'll loan you an older (but still quite functional) air flow meter. Lab type hot wire. Take it home and measure blowby to your heart's content.
Return postage and insurance is on you though.
Greg
If we both make it to OCIC, I'll loan you an older (but still quite functional) air flow meter. Lab type hot wire. Take it home and measure blowby to your heart's content.
Return postage and insurance is on you though.
Greg
06-22-2004, 04:12 AM
#38
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For those interested in the separator I was looking for the CFM in regards to, I ended up going with this one. click here 4453K22 It is simply a high capacity oil filter that uses 1" inch fittings. It filters down to 3 microns. The other one I mentioned above is too restrictive.
This filter seems to flow much better but since it is 3 micron v/s .3 micron I probably won't plumb back to the intake but to the smog pump and allow to smog pump to get some fresh air as well. Maybe I'll even overspin the smog pump.
I'll do a write up of it later.
Andy K
This filter seems to flow much better but since it is 3 micron v/s .3 micron I probably won't plumb back to the intake but to the smog pump and allow to smog pump to get some fresh air as well. Maybe I'll even overspin the smog pump.
I'll do a write up of it later.
Andy K
Last edited by GoRideSno; 06-22-2004 at 04:44 AM.
06-22-2004, 11:14 PM
#39
Drifting
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Here is a picture of the separator. I put a barbed fiting in the bottom so that any oil that collects may be drained. If you do this be sure not to drill through the 2nd layer of metal that is about .5" past the outer layer. Notice the large openings.
Here it is on the car but not mounted yet.
Andy K
Here it is on the car but not mounted yet.
Andy K
06-30-2004, 04:47 PM
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Porsche provides two 1/2 " round openings to vent the crank case blow by gasses back to the intake for the S4 at 316HP.
....or....
Loooking at my spare cam covers, why not machine the holes and run a 3/4 or 1" breather line off new fittings ?
Im still learning about crankcase ventalion and stuff but if the object is to relive as much pressure in the system as you can, the more ventilation you can give it (2 breather lines on each cover) the better correct? Or use bigger breather lines with the two stock locations on the single pax cover.??
06-30-2004, 04:59 PM
#42
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Tony,
Since you have your valve covers off you should do this.
Andy K
How about adding breathers lines to the other(driver side) cam cover?
Andy K
06-30-2004, 08:51 PM
#43
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Somebody help me here. Why pull gasses from the valve covers and not from the oil pan?
If the gasses come from combustion and blow past the rings, then they have to go down the cylinders, and then up the oil passages to get into the valve covers. If you are going to drill holes and install fittings, wouldn't it be better to put the holes in your oil pan and keep the gasses from running up the oil passages to your valve covers. Yes I know, it's easier to get to the valve covers than the oil pan, but doesn't that make sense? Or am I way off here?
If the gasses come from combustion and blow past the rings, then they have to go down the cylinders, and then up the oil passages to get into the valve covers. If you are going to drill holes and install fittings, wouldn't it be better to put the holes in your oil pan and keep the gasses from running up the oil passages to your valve covers. Yes I know, it's easier to get to the valve covers than the oil pan, but doesn't that make sense? Or am I way off here?
06-30-2004, 08:58 PM
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there is a virtual oil storm going on inside the oil pan and way too much oil suspended in the air /gasses . Having the vapors make the trip up to the top of the heads perhaps helps let some fall out of suspension .
06-30-2004, 10:07 PM
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yeah, what Jim said. Your relieving "air" pressure. The oil mist being heavier will drop out of suspension in the air the farther it has to travel.