Welcome to the SR20 Community Forum - The Dash.
SR20 forum logo

Thread: Crankcase Ventilation via the exhaust

+ Reply To Thread
Posts: 1-10 of 12
2014-01-04 02:09:20
Crankcase Ventilation via the exhaust
As mentioned in BenFenner's thread about crankcase ventilation, a method of removal of positive crankcase pressure would be to route it to the exhaust.

Have any of you done this? What were your results at wide open throttle? Were you running an exhaust without a muffler and cat?

I am reading into this more and it seems that there's a potential issue with positive crankcase pressure being developed at WOT and higher RPMs. I'm guessing this is due to too much restriction in the exhaust negating the scavenging venturi effect. For those of you that have done this on SR20s, have you seen positive crankcase pressure at WOT, or have you maintained a vacuum throughout the rev range with partial and open throttle?

I really want to do this, as it seems the best available method for the money:

With an oil seperator combined with this method, you:
- don't lose oil
- there is no oil smoke in the exhaust from burning oil vapor
- if vacuum is maintained through the rev range (this is the area I'm wondering about) you could potentially have better vacuum than the stock method of routing it back through the intake
- related to the point above, you could potentially have better ring seal than stock, compounding the benefits of less blowby and better compression

The obvious best options aside from this available are the wet or dry sump mechanical vacuum pump setups... which can cost you a pretty penny.

With just an oil separator/catch can added to the line going back to the intake, it would be beneficial, but as mentioned in Ben's thread, there'd be no benefit to promoting ring seal. Cleaner intake, less chance of detonation, but nothing to do with improving ring seal.

Venting to exhaust, if vacuum can be maintained throughout the rev range... would be ideal IMO. A best bang for the buck setup.
Last edited by wildmane on 2014-01-04 at 02-11-12.
2014-01-05 03:03:21
I tried it out. I had a moroso PCV check valve made for this exact application plumbed between the valve cover and the downpipe. It didn't work too well, so I went back to just the tube from the VC to the intake before my turbo. Now I have zero oil in my intake tract. I don't use a catch can, but I do have a well baffled valve cover (S14 valve cover on an S13 RWD motor).
2014-01-05 21:15:47
Thanks for the input, helps a lot.

Guess it's either another oil separator or a VE valve cover then..

Just curious, what was your exhaust setup? Muffler, piping size, cat/no cat etc?
2014-01-05 22:18:30
Out running errands, so I cant go into detail. Check my website for what the car has
2014-01-07 05:39:33
I'm debating on a mechanical or electrical vacuum pump.... Gonna make my decision in a week or two. Electrical is easier to setup but don't last as long and I don't know yet how they would ramp up to suck more vapor at the higher rims ... Maybe off maf voltage idk.

A mechanical one from gz motors ports or moroso would work well and only use about 1 hp after it's broken in. I figure I can weld a bracket and mount it where the ac used to be. They last a long while between rebuilds and are reliable.

Hopefully ill remember to post my results
2014-01-07 05:44:22
go mechanical, I am reading bad stuff (short lifespan) about the electrical pumps
2014-01-07 07:02:54
Yea they are getting better with the lifespan thing but still don't last very long.

Gzmotorsports has a kit for the eclipse/talon... Be awesome if I called them up if they would fab something up for us sr20 guys. Bet lots of people would jump on board if they knew the benefits of a steady 5-10 inches of vacuum through the rpm range.

There sportsman pump by itself is about 350... I think its worth it for constant vacuum... Better ring seal... And eliminating octane robbing oil vapors.
2014-01-07 13:23:01
What are we talking about here? $350 for..say...3whp? Anyone got any data on these small engines?

Ring seal is really not affecting performance here as much as you might think. The major power increase comes from reduced drag on the rotating assembly - ie the crankshaft. Those counterweights enjoy the reduced density from lower pressure.

On a formula 1 car or a cup car spinning 8000-15,000rpm for hours at a time this can make a large affect. On a 1991 Nissan Sentra? Route to the intake and turn up the boost 0.1psi.....

Actually would genuinely be interested in seeing a comparison but doubt after spending $500 to fab this up anyone will be able to pay for a few dyno pulls.

2014-01-07 14:04:25
To me its logical... the pluses outway the one bad thing.... cash. the performance increase may not be the greatest but ill be happier daily driving the car
2014-01-07 14:14:44
Don't get me wrong, I highly respect the motive to chase the HP my friend. Just want to be sure everyone understands this is next level sh*t (pwer/$$).
I think the pump is a much better idea then an exhaust system. The lower flow rates of our smaller engines probably would make this not worth it. Most applications where I have seen that used is 4000+HP with absolutely massive flow rates and short high RPM WOT runs only.

+ Reply To Thread
  • [Type to search users.]
  • Quick Reply
    Thread Information
    There are currently ? users browsing this thread. (? members & ? guests)

    Back to top