Thread: oil catch can pcv 20v valve cover question

so i have a 20v valve cover with a mini catch can tee'd in between the pvc valve going to the intake mani and i get quite a bit of oil in between there. I got a greddy catch can i want to put on. Can i just run a hose from the pcv hose to the catch can and block of the port on the intake manifold where the hose would usally go?

thanks for any input. Ive done some searching but didnt know if this would work blocking off that port on the intake manifold where it sucks air in. What would happen if i blocked that off?

i wanted to route mine just like this. Pvc hose to catch can then the port on the side of the vc to catch can.

Super trick oil catch can - G20.net - Forums

Absolutely not.


The PCV would no longer work at all. That one section of the PCV system is designed to handle the lesser amounts of blow-by at idle and/or partial throttle (the other two sections of the system are for WOT operation) and uses the vacuum created in the manifold to vent the crank case and apply a bit of vacuum to it. It's not the most important thing in the world, but it helps to keep oil and gasoline vapor from building up in the crank case, or any pressure from building up, and promotes ring seal along with proper oil seal life, etc.


That would defeat the purpose of that section of the PCV system. Pointless.

Why don't you let the engine burn it like it was designed to do? Get rid of that stupid catch can, you don't need one on it.

That's what I've always said too. The only benefit is a cleaner intake manifold/throttle body/valves and to some it's worth it, to most of us it's a waste of time.

This is a fun one, Danja and I played around with it about 2 years ago. I had a serious case of oil blow by and was seeing what I can do to reduce the amount of oil went into the manifold.

Catch can is the best way to go, but it gets annoying to clean it. You can bleed the PCV to atmosphere and cap off the intake manifold but then you will increase your emissions. Plus having the vacuum suck out the blow by reduces the crank pressure, thus the pistons move around easier.

so the link to the guy that has it routed the same way i want to do is incorrect? I have the mini catch can from homedepot inbetween and it gets quite abit of oil. I heard the 20v valve covers had one built in? I def want to run one because id be happier with that oil not going into my intake system.

thanks for the responses

Yes, while it is a really amazing looking piece the hose coming from the top-left corner of the valve cover should not go to that catch can. It should see vacuum from the intake manifold.

However, the hose coming from the top-right corner of the valve cover should not see vacuum from the manifold, it should connect upstream of the throttle body (or can vent to atmo).

So those two need to be kept separate.

If your goal is absolutely no oil in the intake system yet still keep a good functioning system you'll want to vent the crank case and top-right valve cover provision to atmosphere using a catch can.
And then get a separate catch can (you have the Home Depot one right?) and put that in line between the PCV valve and manifold and drain it occasionally or design it to self drain.

If that's all too much work you can just vent everything to atmosphere with a catch can like that guy did in your link above. However it's the easy way out with diminished engine operation.

(Okay I guess you could block all the PCV stuff if you really wanted except the top-right valve cover port and just vent that thing. Talk about a bad idea though.)

Did you have this oil issue with your old VC?

All SR20 valve covers have built in oil separators (some have more than others or different pathways) but I haven't done my homework on the PCV valve section of them. I'm sure there's some form of oil separator in all of them... They aren't perfect though.

over on g20.net we have noticed greater oil consumption on the RR engines which I believe have the same internal baffle in the VC. This thread depending on the answer to my question above may actually solve our dilemma. It may be the VC and PCV may be the entire reason the RR have disappearing oil. I'm on my third SR car and this RR is the first one to ever lose oil. The other two were a highport and a lowport.