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Hey, I've gathered from a couple recent topics here that it is quite common and accepted to have a significant amount of positive crankcase pressure. From everything I've learned and know about engines in general, this is *never* desirable.
First off, is there any reason that you know of for this to be present? Is it in some way desirable? Basically, am I missing something here?
If I understand correctly though, it would be nice to pull a mild vacuum in the crankcase. Has anyone made progress in accomplishing this? My initial reaction is that the problem is too large to be solved by just scavenging effects/pulling vacuum via the exhaust (plumbing a fitting in and running it to the PCV or something - basically using laminar flow to draw gasses out of the crankcase), so I would lean towards a small electric pump to pull vacuum. I'd be very interested to see if anyone has attempted this. I think it could benefit the engine greatly, mostly just by allowing it to be less strained in revving. Obviously power increases would be minimal, if any.
Back in the day (the 50s) a road draft tube was used to pull the crankcase pressure out. This was canned due to emissions, and polution.
One drawback to your idea is the crankcase gases would be unburned. They will contain raw oil, which will plug the mufflers and damage the cat, along with spraying the road and cars behind you. It would need to be filtered somehow.
I started a thread about the 04 valve cover improving it, but never got an answer. This will be an interesting topic
I use KrankVents on my sc'd S. This creates vacuum in the crankcase. When I dynoed at Comptech, we removed both of my Krankvents (@ the pcv/intake manifold and crankcase breather), and boost entered. Inital dyno was at 299 whp, after some pressure (.2-.3 psi) - 290 whp; whp dropped even more @ 2-3 psi to 285, and when more boost entered (>4psi), whp dropped to 270. The stock pcv doesn't do a good job with keep pressure out (at least for FI application).
When we reinstalled the KrankVents, 304whp. Comptech is looking to adding this with their kit.
I think my FI application displays an exaggerated example of how vacuum can help our engines, and how pressure lowers power output. I would say in NA conditions, some pressure is created in the crankcase, although minimal (~.2psi, this is what we got when we just used the pcv/manifold krank), but the same amount of vacuum is created.
The pcv-intake can basically replace the stock pcv, but I have mine inline to keep boost out, and any positive pressure to be released.
I also have a catch can inline
The crankcase-intake hose krank allow positive pressure to leave, but doesn't allow air to enter.
Very cool! Thanks for the replies so far. I'm off to bed for tonight, I'll be interested to see if this goes anywhere.
I'd be more than willing to mess around with getting a system similar to Gary's on an NA car, but I can't guarantee any dyno results, just a subjective review.
Good observations, billman. I'll be mulling over this in class tomorrow I'm sure!
would those krankvents create the same pressure in the valve cover with an NA setup? I would be interested in doing this myself if this should work. Heck I would even be the guinnea pig that gets used for it.
I used the krankvents to stop my oil burning while tracking the car because it stops the oil being sucked into the intake. Puts a vacuum in the crankcase too...you hear the pop when you pull the dipstick
[QUOTE=thetz99,Feb 12 2006, 11:07 PM]I used the krankvents to stop my oil burning while tracking the car because it stops the oil being sucked into the intake.
I don't burn oil until trackdays where I would go through a quart a day. After the krank vent install, no oil drop after 3 track days. I'd say it stopped the intake from sucking it out.
And the sound when I pull the dipstick is a pop with a sucking sound...
02-12-2006, 07:50 PM
Crankcase Evac?
Comptech is looking to adding this with their kit.
