Crankcase Evac

[jmgtp]

Is crankcase evacuation possible using the exhaust on stock equipped exhaust manifold car?

something like this:

http://www.jegs.com/i/JEGS/555/52210/10002/-1

If something like the above were to be installed in the downpipe where the exhaust gas volume/speed would be maximized would it pull vacuum? The car has stock exhaust manifolds, x-over and downpipe and aft of the downpipe is a high flow 2.5" cat and full mandrel bent 2.5" catback.

The thing I like about the exhaust evacuation over the pcv is that as rpm and engine output increase so does the speed/volume of the exhaust and in theory that should create more vacuum. The pcv on the other hand, at full throttle, has no manifold vacuum and isn't doing much to evacuate the crankcase.

I've got a bit of a blow by issue. The stock pcv system isn't keeping up, there is literally no room to mount a vacuum pump unless your willing to ditch the a/c, and the electric pumps are for race duty/non continous only.

I'm stuck between a rock and a hard place. Ideally the solution to this problem is a rebuild but I'm not willing to do that yet. It otherwise runs great and I don't have the time or coin for a rebuild anytime soon.

[jmgtp]

another thought: if I were to try this, would it make more sense to install as far down the exhaust as possible where there is less backpressure? For example, if I were to install it in the downpipe there is X amount of backpressure caused by the cat converter, muffler, etc. If I were to install it just before the tail pipe there is no muffler, cat, etc to restrict flow and there should be less back pressure. Of course that means running a ridiculous amount of tubing. Ideally for fitment, I'd want to install it in the downpipe so things would be easy to route but is there too much backpressure there?

[jmgtp]

Hate to be the only one replying to my own thread but... after getting no responses I decided I had nothing to lose, save for ~$50 and gave it a shot! I did a good bit of Googling and it looks like a few LT1/LS1 guys tried it with moderate results.

I got everything I needed on ebay for very cheap. The evac tube kit included the tubes, check valves and breather/baffle. And I picked up 50 ft of 5/8" heater hose, for $10. Thanks again ebay.

I welded in the evac tubes aft of the muffler and about 12" before the exhaust tip. So they are in a location with little to no restriction. I replaced the front cover with a modded rear valve cover that I drilled for the baffle. I lose the oil fill cap but the baffle pops off easy enough. For now I 'T'd the two tubes together and ran it to the front cover.

The idea behind the evac system is to have a closed engine and pull some vacuum in the crankcase. This in theory draws the blow by out through the exhaust and creates better ring seal as well as less air pumping losses underneath the pistons for a mild increase in output.

I kept the PCV line. Since the pcv valve acts like a checkvalve as well, if the crankcase vacuum from the evac tubes was greater than manifold vacuum the check ball would close so the evac tubes wouldn't be trying to fight the intake manifold. Yet at low rpm/idle where the evac tubes would be doing nothing the pcv line would allow manifold vacuum to be applied. I eliminated the breather line since this line is technically open to atmospheric pressure and that would make pulling any vacuum in the crankcase nearly impossible.

Impressions:
My goal going in was to eliminate the valve covers from seeping oil, which in my theory was caused by the excessive crankcase pressure from blow by. In this matter I seem to have succeeded, the valve covers no longer seep oil. Maybe this means its working, maybe it means they're just sealing better, maybe doesn't mean a thing at all. I ran a vacuum gauge to the front valve cover and taped it to the windshield so I could see what was happening in real driving conditions - It never pulls any sort of real vacuum in the crankcase. Whether this means that my evac setup is worthless or not I do not know. Even if the tubes were working perfectly, I don't think my engine is sealed tight enough to create a vacuum. It may not be pulling vacuum but I think at least it may be relieving the crankcase pressure better than the pcv and breather line alone.

Ideally, I'd be running a real vane type vacuum pump. The only feasible place to mount it would be where the a/c compressor is and I just cannot give that up. I'm still toying with the idea of an electric evac pump that would kick in under wot and maybe pull some real vacuum. I'd like to see at least 10" in the crankcase since that should be good for a nice little power increase. For now, I'm not seeping motor oil and that has me satisfied.