Crankcase Evacuation
 

Has anyone on this forum ever tried crankcase evacuation?

evacuation as in using a vacuum pump? No. Nobody here runs enough boost to need something like that- and our engines surely aren't big enough on displacement alone.

I'm not thinking about using a pump but rather using a hose which attaches to the exhaust after the turbo. The fluid movement of the exhaust flowing through the pipe will create a suction effect and suck the piston blow by into the exhaust. The Idea is that you can use more flexible piston rings which create more blow by but trade off for that by creating less friction between the pistons and the cylinder walls. You then turn up the boost.

Dident we have a discussion about this like a few months ago? I think it ended with everyone saying its not worth the time and $$

In theory it shouldn't cost that much more if you are already rebuilding an engine. Feel free to post any objections to my idea or add parts to the list below.

Requirements:
Rings
Pathway to crankcase. (I still have to do some analysis on this)
Hose
Catch-can
more hose
a correctly aligned inlet to the exhause.

you think adding a ventri into your exhaust to pull vacuum out of your crankcase is really going to help you run that much more boost?

Sure. Try it, find out for yourself, then post your findings here. I'd be interested in seeing how much (if any) vacuum an exhaust type evacuator will create. You may have to create a venturi (restriction) in the exhaust in order to produce enough vacuum in the hose to the crankcase.

Vibrant sells some parts to do this...like a O2 bung looking thing cut at a 45deg angle for the exhaust, and a nice billet adapter for your oil fill cap to evacuate the engine. I guess it's better than nothing?? But what could you gain, 5hp? I have no idea.

The supra guys seem to yield large power gains but then again they are dealing with larger displacement.

As for power gains I honestly have no clue.

What he's talking about is more common on older 1/4 mile V8 cars. They put a piece of pipe cut off at an angle in the exhaust such that it will create a strong vacuum when the motor is wide open. Works good on V8's, it's anywhere from 30-50 HP as it pulls a vacuum and kills windage dramatically. But I'm not sure I'd do it on a miata. But try it, it may works well.

My Hot Rod instructor used an electric pump for his drag car, I would imagine using a pump would be way easier.

That was my original thought as well. The downside to that is that it adds cost and complexity. The air pump would be an added part which could fail.

On the other hand I didn't know if an air pump could create enough air flow for a long duration. Not only does it have to pull enough air and junk from the crank case but for my application it needs to run for extended periods of time, not just 16 - 9 seconds. It is cool to see some experienced guys using the electric air pump. Apex do you have any idea what kind of air pump your instructor was using?

No but it was a 9 second bracket racing car, so it definitely survived a lot of abuse. You don't have to have much vacuum in there (right?), and if you think about it, it would be easier in the long run. Instead of welding a bung on the exhaust and fabricating hard lines to connect to the block, you would just have to mount the pump and you could use flex lines since they wouldn't have to deal with nearly as much stress as an exhaust tube. Plus if it DID fail, its not like there would be catastrophic failure, and I would imagine it would last a while. I don't see an issue with having a pump on for a few hours straight as long as it has some air around it to cool it.

Is it ok if I do a cross forum post? I found some information on a honda forum that seems to be valuable to this discussion.

You are talking about something different. You speak of something that helps reduce excessive crankcase pressure. The setup bigboy describes will pull a hard vacuum on the engine's crankcase, removing most of the air. This drops windage, which is a big HP thief at high RPMs (amongst other things). I damn sure wouldn't run softer rings though. That kind of motor is for pure drag racing where it runs long enough to heat the tires and make a pass. Really I wouldn't try to put a vacuum setup on a street car. It's usually for drag racing only.

Well here goes nothing. Slap me if you don't like it.

http://www.honda-tech.com/zerothread?id=1199935

Oh that makes sense Pat.

I ran a venturi with a oneway valve on my exhaust with my last motor. After about 20K miles of boost all of which was too rich (I believe), this was before widebands were commonplace, I started having excessive blowby and poor leakdown #'s past the rings. I got the venturi from summitt or jegs. plumbed it into both sides of the valve cover. opened up the valve cover baffles and placed a cut up K&N airfilter in there to prevent it from sucking oil right out of the valve cover. And believe me it created enough vaccum at full throttle to do just that. ran it for a year then bought a another motor . the original motor still sits on its stand waiting for the kids to graduate, then I can afford to do the build I would like. talked to a man from florida about this before doing it. He dissappeared a couple of years ago. he had made a coldside supercharger manifold and a nice varible progression throtle cam. can't remember his name