hey guys,

i just learned about different PCV sizes and i'm wondering what modifications on your engine might make a bigger valve necessary?

any ideas?

thanks
kay

 

The main purpose of the PCV is...

• to remove exhaust gasses that push by the piston rings

• to remove vapors of any gasoline that at drain past the piston rings during startup

The capacity of the PCV is set so that it can do both.

In the process, it pulls out 100% of the exhaust gasses out and a bit more air so that the crankcase is kept a a slightly negative pressure.

Outside air then pushes in through the breather on the opposite valve cover and sweeps any gasoline vapors out through the PCV.

Modifications or other items that would require more PCV capacity would be...

• richer gasoline-air mixture
• looser fit of pistons to bore allowing the piston to rock and therefore preventing the rings from sealing as well
• worn out rings

If you have any of those types, or similar, situations you would consider a larger-capacity PCV.

 

There's not a lot of info about PCV valves out there. I ran into problems with my buddy adding a supercharger to his 4.6 - ended up using a PCV from a blown mustang, seems to work OK.

I bet for the vast majority of builds the stock PCV is perfectly fine. Once idle vacuum gets really low or forced induction or something then it's worth doing some research.

The only place I've found with useful into is MEWagner.com Of course they're trying to sell you their adjustable valve. Worked on me.

 

Eightball:
There is a really cool, adjustable PCV valve that can be fine-tuned to the vacuum signal of your engine, but they're not cheap at $130 each. Here's a pic and a link.




http://mewagner.com/?p=444

Rodney

 

oh thats great. maybe i try this one someday.

i was just asking because sometimes you see guys with 2 PCV'S for example and i was just curious if i have to improve mine too after i "massaged" the engine a bit. also the breather outlet is bigger in diameter than the stock PCV inlet.

last time i floored it hard it splashed oil all over the engine out of the breather grommets..so i assumed it might not be pulling enough vacuum through the PCV.

for a proper working PCV..wouldnt it be necessary to have the entire engine kinda "sealed"? like every gasket has to have a perfect seal?

i remember that later i found some loose bolts on the lower half of the front cover and wonder if thats the reason the PCV would not function properly. it leaked oil down there...

 

When you floor it, there is no vacuum to operate a PCV.

You cannot fix this oil splashing by changing or adding PCVs.

You need to fix the problem that is causing pressure in the crankcase.

Your piston rings may not be not sealing well.

Measure your compression. Then squirt some oil through the spark plug hole and check compression again. If compression rises significantly, then you found a big problem.

 

I have run a breather on the opposite valve cover with a hose connected to the air filter housing that will aid in relieving some internal pressure.

 

you mean an additional one?

car came from the factory with a breather on the drivers side and PCV on the passenger side

i couldnt find any excessive blowby ... it would also blow the dipstick or you would find at least some oil on the underside of the oil filler cap, wouldnt you?

as for the set-up: i went with fabricated aluminum valve covers where i'd have to drill the holes myself. i put in some rubber grommets with built in "baffles". some guys on here also told me that they splashed their oil over the engine after that and some RTV around the grommets would help...and so far it didnt splashed again after i used some RTV and reved her "a bit" on the street..didnt tried red line yet. last time it did the oil splashing i did a burn out...didnt dare to do it since then.

the PCV, breathers and the vacuum lines all look totally clean inside...i would have expected to find at least a little bit of oil stains. not that it is meant to be totally full of oil but..you get the point

 

Is the breather on the drivers side connected to the air cleaner that sits on the carb?

 

yes it is...but i doubt there is enough vacuum in the air cleaner area to help significantly. but i might be wrong. still keeping it connected though

 

It helps at wot. As Gary suggests, if it persists you need to repair whats causing it. Usually its the rings.