i have breathers on my valve cover but at high rpms some oil comes out through the breathers, have you guys considered using an oil catch can setup with a breater? I was thinking about getting a catch can with a breater and two ports, one going to each valve cover. what should i do? i'm trying to keep my engine bay clean

mmhmm maybe noone runs it

Do you have a working PCV valve and valve covers with baffles? If you do, and you're getting oil out the breather, you have excessive blow-by.

noboostnogo - im gettin ready to run a breather in my driver side valve cover, and my PCV valve is in the passenger. this is a daily driver, i dont hit RPMs over 3000, think ill leak? and if i do what to do to fix it? im running it for appearance mostly, but dont want oil in my engine bay.

you need to find the reason why the blow by - you are the first one that has reported it that i have read.

interesting.....




The two big air breathers are the ones that leak, the other chrome ones have a sealed grommet. I do not run a PCV valve, i asked all the guys at my local speed shop and they all recommended NOT to run one.

For some reason i dont think its blow-by but instead because the grommets are the "see through" kind i think at higher rpms oil comes out due to ~70psi of oil pressure

what causes blow by btw?? i remember hearing about it when i was in the turbo cars scene. a while ago

honestly i have no clue. at lower rpms mine does no leak so i wouldnt think so.

blow by, what 'I' think its for is that the crank case needs some vacuum? so they use that for ventilation. hence the PCV valve stands for 'something Crankcase Ventilation. and if its not on there it will blow your dipstick out and push out oil.

Blow by is pressure that 'blows by' the rings, into the crankcase.

what should i do to avoid this then??

PCV valve is the only way i know. anybody else?

Why? Is yours a balls out high hp race only car or a street car? The only reason not to run PCV is because it influences the mixture and pollutes the intake, something that might be an issue in an all out race car, however if you run it on the street mainly put the PCV back in, you're not WOT most of the time anyway, you will not see the difference...well...actually you will, your oil will deteriorate faster and you'll have a sticky mess in the engine bay.

If you're worries about cosmetics, earls has a nice looking AN style PCV:

what kind of car is that twin turbo?? not a camaro.. the strut tower braces arnt.. there. and you have diff windshield wipers.

Excessive blowby would be caused by bad rings... Some blowby is always present though, I think, so no matter what you are going to have some vapors coming out of the breathers. The vapors condense as they cool, so maybe that is what you are seeing is condensed oil vapors coming out of the breathers...?

A PCV w/catch can is the ideal setup for a mostly street driven car.

No PCV is not all that great because the blowby vapors are somewhat acidic and moisture laden which is bad for the oil and metal when they condense in the crankcase. The PCV system serves to "flush" these vapors out increasing oil life.

If you run a catch can you can have all the benefits of the PCV system, w/o the down side of the crap getting all up in your intake. Or, well, it at least significantly decreases the amount of crap that gets in your intake.

There was a great extensive thread about the whole concept of the PCV system on LS1tech.com that I would reference here, but of course now that I want to, I can't find it...

I apologize for the somewhat inarticulate post, but I hope it makes sense...

77 corvette

PCV - "Positive Crankcase Ventilation". Interesting name since it uses vacuum to provide the positive ventilation. But, since it replaced the passive "road draft tube" system that used the somewhat lower pressure under the car and somewhat higher pressure in the engine compartment to drive a small flow through the crankcase and remove blow-by gases, it makes a little more sense when viewed from that perspective. Since those gases contained unburned hydrocarbons, PCV was an emissions reduction device. But, it had other advantages - read on.

The crankcase benefits from being in a relative vacuum state. A couple of reasons, but from a performance standpoint, the less air there is in the crankcase, the less resistance the pistons have moving up and down. You might not think that would be all that significant, but a racer buddy put a crankcase evacuation pump on his 9-sec 454 '84 Monte Carlo a couple of years ago and picked up a consistent tenth. The first one he put on wasn't a very high dollar unit, and he could tell when it was failing because his ET's would start to rise. But, for a street car, or mild performance strip car, the effect would be less noticeable (if at all, especially on a street car).

The other reason is crankcase contamination - those gases don't do any good when they stay in the crankcase. Based on your photos, I would take off the driver side breather and put in a PCV valve connected to the bottom of the carb or that spacer - a runner is not a good place to put it, because there is a small flow at all times through the PCV, and you'll tend to lean out that cylinder if you put it to a manifold runner. If the non-filter looking caps are also breathers, I'd replace the one on the driver side (same side you put the PCV valve on) with a cap. The opposite side can have two breathers, that won't affect anything.

And, the hole you're using for the PCV valve should have a baffle on the inside of the valve cover to keep the PCV from sucking up oil.

Bottom line - your speed shop gave you bad advice.

could you explain how i would hook that up?? valve cover with pcv to catch can to intake?? a catch can with no breather??



five7kid

Thanks for the explanation that really helped. What do you personally run in your cars??


BTW this car is no where close to being my DD, its my weekend/strip car for right now but it is slowly turning into my car that i only drive to and fromt he track and race while im there..

PCV valve on one cover and breather on the other.

Your description of the use of the car pretty much mirrors mine with the '57.

I think the way it's done is: breather in one cover, pcv in the other, then hose from pcv to can, then other hose from can to intake/carb/other vacuum connection.

But, as you say the main use of the car is actually the races... I was making my recommendation based on primarily street use. I'm not sure about race applications and stuff like that so I would defer to five7kid.

Thanks for all the info i will def. get a pcv setup going. Thanks again

That is correct. The picture of the fancy set-up above isn't that way, as the catch can has the breather. Hook it up like that if you expect the PCV to be overwhelmed under power (which is likely because vacuum drops under WOT).

If you are referring to my system, the catch can is doubling as the breather and is mounted there so that there's no oil mist on the valve covers. Also, the PVC does not always evacuate the crankcase (WOT), so whenever there is crankcase pressure being forced out, it collects in the catch can.

using a pcv on a valve cover, hooked to vacuum with a catch can in between accomplishes nothing if the can is vented because the PCV will draw from the path of least restriction, being the breather and not the crankcase.

Hooking it up that way assumes the catch can is not vented.

LS1 guys often use a system like that because they tend to get a lot of oil into the intake from the PCV.

So the way yours is hooked up is from vavle cover to vented catch can with no pcv and the other valve cover with pcv to vaccum?? Is that just as efficient as using a non-vented can and vacume from intake to can and can to pcv on VC?

"PCV" is the total system. I think what you were trying to say is no PCV valve on the side with the can, and the PCV valve hooked to vacuum on the other valve cover.

In that case, yes.

Ahhh, yes. Sorry about that. I was assuming a non-vented catch can. And, also, yeah, I learned what I know about PCV from ls1tech.com.

yup thats what i meant.


I think i will end up going that route then.

guys for all the info and i hope this helps someone else in the future with my same problem.