PCV and Catch can questions.

[Robochan]

The stroker motor in my corvette has a fair amount of crank case pressure. It currently does not have a pcv valve but in it's place is a non baffled catch can. During hard driving, expecially track time the catch can fills with oil and then proceeds to allow dirty air back into the intake.

 

At first I got scared and thought it was weak rings and excessive blow by but after running compression tests and extensive online reading I found that it's common with most LS motors and way more prevalent in stroker motors. Possibly do to the piston traveling too far into the bore and allowing a little bit of air by. The motor is healthy as far as the dyno goes as well.

 

There are a million ideas on various forums but my question is do I need to have any of the crankcase air return into the intake at all? It is fed back in after the air meter but i still don't think it would matter. Their is also a line from the valve cover to just after the air cleaner and before the air meter but it's completely dry of oil, as well as the intake up to the throttle body.

 

My current plan is to run a larger baffled catch can or to vent the oil filler cap and run 2 catch cans but I would really like some input.

[spectragod]

I'm using a pair of these on my Marauder.

 

http://www.42draftdesigns.com/ultimate-oil-catch-can-1-2-npt/

 

One on each side, back into the air intake after the MAF.

 

If you are boosted, you will need lines that won't collapse with boost/vacuum, I wound up using XRP lines, a touch on the expensive side, but they work.

 

http://www.xrp.com/

[Smokey]

There are a million ideas on various forums but my question is do I need to have any of the crankcase air return into the intake at all? It is fed back in after the air meter but i still don't think it would matter.

 

I'm not knowledgable on LS motors, but in most I've dealt with the PCV to intake is purely for emissions purposes and helping scavenge the fumes. No need to run it to the intake if it's causing issues, but you'll want to run a catch can with a filter to release the pressure.

[aussiek2000]

What style PCV is on your engine? The LS6 style valley cover is less prone to sucking up large amounts of oil compared to a valve cover.

[zeitgeist57]

I know a guy that bought an '01 Z06 new and had an aftermarket catch-can installed for the blow-by. It probably gets worse with age, but I can definitely confirm the LS6's at least came factory with a good amount of crankcase pressure.

[Robochan]

the PCV to intake is purely for emissions purposes and helping scavenge the fumes. No need to run it to the intake if it's causing issues

 

This seems like the best solution but are there any negatives to this route?

 

What style PCV is on your engine? The LS6 style valley cover is less prone to sucking up large amounts of oil compared to a valve cover.

 

The car has a FAST intake, ls6 heads and a LQ9 block. I assume its still the LS6 style. The hose comes out just under the throttle body.

 

I know a guy that bought an '01 Z06 new and had an aftermarket catch-can installed for the blow-by. It probably gets worse with age, but I can definitely confirm the LS6's at least came factory with a good amount of crankcase pressure.

 

That seems to be the verdict on all the LS motors. Lots of blow by and oiling issues. Bitter sweet to hear its all too common.

[Geeto67]

if you look at an old chevy small block the breather is a mushroom thing stuck in the valve cleaner fill hole that vents to air. Before that it was a hose in the block that vented into the air cleaner or a 90 degree fitting from the oil dipstick to the holley carb. Other than reducing hydrocarbon output by filtering oil mist back into the engine I don't see the point in it connecting to the intake.

http://img.photobucket.com/albums/v426/prostreetcamaro/P1000351.jpg

 

I did find this article:

http://www.lsxtv.com/tech-stories/engine/tech-crankcase-pressure-control-oil-and-air-control/

 

Moroso’s Air-Oil Separators plumb directly into the car’s PCV system. Using mesh filter media, they capture the majority of the engine oil that escapes the crankcase and is normally sent back to the engine through the intake. “Removing this oil mist before it reenters the engine reduces detonation, and deposits on the intake track, including the valves themselves,” according to Moroso’s Thor Schroeder.

 

could be marketing mumbo-jumbo to sell you a moroso oil separator bit it makes some sense, no oil mist to burn fewer carbon deposits.

[Robochan]

The vent on my valve cover is to pull clean air into the crankcase and the pcv from the intake is to push the dirty air out. I believe thats the same on the SBC, the valve cover is pulling air in, not pushing it out. The "oil separator" seems to be nothing more than a baffled catch can. It just gives the oil more time and more surface area to condense from the air.

[Geeto67]

The vent on my valve cover is to pull clean air into the crankcase and the pcv from the intake is to push the dirty air out. I believe thats the same on the SBC, the valve cover is pulling air in, not pushing it out.

 

Depending on year on the old small blocks, one side valve cover would be the intake into the crank case, and the other side would be the vent. Anybody who has owned one of those old setups can attest they are always covered in a little bit of oil. We used to call them "breathers" because really I think they work both ways. I remember when the hot setup was to just replace them with small K&N filters.

 

It's been a long time but I am pretty sure my pontiac requires manifold vaccum to operate the PCV. I have one hose from the intake to the valley cover PCV and then a "breather" in the valve cover. Do the LS engines require manifold vacuum to operate? if so, where does it hook up?

 

you need an air intake and a vent. all I am saying is the vent doesn't need to go back into the intake to divert the oil mist back into the engine for emissions purposes. It still might need vacuum.

 

 

The "oil separator" seems to be nothing more than a baffled catch can. It just gives the oil more time and more surface area to condense from the air.

That's all it is. The filter pulls oil out of the air. if your vent side is the one hooked up to manifold vacuum, then pulling the oil mist out of that air would do something.