View Full Version : My apologies...another ls3 pcv thread :(


Carguyrob598
01-11-2012, 08:01 PM
I am installing a ls376/480 crate engine in a factory five cobra kit. Right now I have my 2 valve cover breather ports hooked up to a filtered breathable catch can and the valley breather still hooked up to the throttle body as it was delivered. (sorry I don't have any pics right now, will post some tomorrow). Is my current setup ok? I have -6AN hoses on the valve cover ports to the catchcan. I don't particularly want oil in the manifold so I was planning on T-ing the valley breather into the valve cover hoses and run it to the catchcan too. Is it ok that the catch can is filtered to the atmosphere or does it need to be sealed? and if it is not sealed will it blow oil vapor all over my engine compartment? Thanks so much for the help, sorry if these are redundant questions, I just haven't been able to find answers to my exact problem. Thanks.

Mike454SS
01-13-2012, 07:40 AM
If you're going to run a MAF, you've made a vacuum leak.

GM gets crankcase air from the air intake after the MAF sensor, because the lifter valley tube is pulling it through there and into the engine.

If you want to run a catch can, I'd get your fresh air to the valvecovers from after the MAF, then put a sealed catch can between the lifter valley and the intake manifold.

Carguyrob598
01-13-2012, 10:08 AM
Thanks for the response, that makes a lot more sense now. After some more research I'm thinking about just running it the way GM intended. Thanks for the help!

DietCoke
01-13-2012, 08:59 PM
LS3 style should look like this with a can. :cheers:

DietCoke
01-13-2012, 09:01 PM
If you're going to run a MAF, you've made a vacuum leak.

GM gets crankcase air from the air intake after the MAF sensor, because the lifter valley tube is pulling it through there and into the engine.

If you want to run a catch can, I'd get your fresh air to the valvecovers from after the MAF, then put a sealed catch can between the lifter valley and the intake manifold.

What does a vacuum leak have to do with the MAF? Crankcase air is more or less sealed off from the combustion chamber and intake manifold (why do you think the factory pcv uses the intake charge to evac crank vapors? durr), it isn't going to affect any metering. That being said, a car should be tuned with a breather if you are going to run one.

Carguyrob598
01-13-2012, 10:03 PM
Thanks for the diagram. What about the driver's side valve cover? Cap it off? Thanks!

DietCoke
01-14-2012, 12:23 PM
CAp it or run a breather. Doesn't matter (I need a breather on mine)

Carguyrob598
01-14-2012, 06:14 PM
Thanks Diet. How is the driver valve cover barb run from the factory?

DietCoke
01-14-2012, 09:22 PM
Mine was capped. It's still capped, but you could run a breather there. Mine is on the oil fill.

Mike454SS
01-17-2012, 08:45 PM
What does a vacuum leak have to do with the MAF? Crankcase air is more or less sealed off from the combustion chamber and intake manifold (why do you think the factory pcv uses the intake charge to evac crank vapors? durr), it isn't going to affect any metering. That being said, a car should be tuned with a breather if you are going to run one.

Look at your own diagram. When there is vacuum on the intake side, it pulls air through the crank case from the intake bellows after the MAF sensor...it's pulling MAF metered air...if that hose from the bellows to the valve cover is open to the atmosphere, at idle and light throttle, it's pulling unmetered air.

When you're at full throttle it's not a vacuum leak because there's no vacuum. If you have a lot of blow by in your setup, yes the stock system can result in pushing that air back the other way into the intake bellows, and that's why a lot of real high power drag engines run breathers instead of PCV.

There's really 2 solutions to a need for breathers instead of a "stock style" PCV system...speed density tuning is 1 solution, no MAF in the mix means it's all calculated from plenum pressure anyways, and doesn't matter what path air takes to get into the plenum. The other solution is completely remove PVC from the equation and ONLY run breathers. If you cap the intake behind the throttle body, and cap the lifter valley, and just put a breather where the oil cap was, you're good to go, blowby isn't going to cause a pressure issue, and you won't get oil in the intake manifold...you MIGHT get oil dripping from the breather, and in that case, put your oil cap back, and plumb both valve covers to a catch can, then put a breather on the catch can...it shouldn't get wet as easily...PCV is really just an emissions thing anyways...and if you're built enough that you're making enough power to the point where blowby is a big deal...you probably don't care about emissions.

Once you've done that, you can probabaly ALSO look into some type of a crank evac system instead. Something that will use exhaust to pull vacuum on the crank case.

1lejohn
01-20-2012, 03:01 PM
If you loose the green hose going from the valve cover to the T-body and add a breather on that same cover. It works just fine. The motor when under vacuum pulls air and acid mist etc. from the valley cover and runs it throught the catch can and returns it back into the intake and burns it. The breather will allow the motor to take in or exhaust what ever it needs to do.

Mine is like that and has little to no oil mist coming from the breather. My little air water seperator for an air compressor works great at catching and dropping out the oil from the PCV.