Thread: How do you choose the correct PCV valve?

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So I have a 350 that had breathers in the valve covers, I want to install a PCV valve. How do you go about choosing the correct one? I went to the local parts store and got one that was for a 350(so I was told) I get everything hooked up and now it runs like it has a bad vacuum leak. The motor is 10:1 with a mild cam nothing special but it's not stock either. Are there hi performance valves that I should be looking for?

i would think the crankcase would need to be mostly closed to garner enuff suction to make the pcv valve function . if you are running dual valve breathers then you should`nt want to run the pcv valve .. make any sense ??

Does the line to the PCV come off the carb above the throttle plate? If your hooked up directly off the intake manifold it might be causeing your problem. I always run a breather on one valve cover and the PCV off the other.

Thanks for the replies. I had a breather in each valve cover I removed one and replaced it with a grommet and PCV valve. The line to the PCV does come from the carb above the throttle plate.

I'll post a pic when I get home this evening. I had a Road Demon 625cfm vac. secondary carb on the motor. It had no provision for a PCV valve on it. I drilled and tapped a hole in the carb spacer for it. This is below the throttle plate where I thought it was supposed to be. The Demon was a problem from day one, so I swapped it for an Edelbrock 1405 600 cfm unit from a well running motor. This carb has a provision for the PCV, so this is where I am now connected and yes I did plug the hole in the spacer. It looks as if it is above the throttle plate but it may not be.

Originally Posted by ceh383

................I swapped it for an Edelbrock 1405 600 cfm unit from a well running motor. This carb has a provision for the PCV, so this is where I am now connected and yes I did plug the hole in the spacer. It looks as if it is above the throttle plate but it may not be.

That's where I run the PVC on my 350, it is the large port in the front center of the Edelbrock.

I know this may sound elementary, but from my understanding of how a SBC breathes you want your breather on the drivers side VC and the PVC on the passenger side. I'm not suggesting you have it reversed, but the PVC valve itself is also directional.

On my truck it's the opposite and has been for years (meaning I didn't change it), the PVC valve is on the driver's side valve cover and the breather is on the passenger (although there's been few of those) side.

Well, thanks for the input. I think I found the problem. It just happened to show up at the same time I put in the PCV valve. Low fuel pressure, the regulator took a dump. It seems to be running fine now.....timing is everything.....

Does it matter if the PCV valve is actually "in" the valve cover? I have one of those "breather looking" push in deals with the tube out the side.. I call it this because although it looks like a breather, there are no holed in the bottom of it like a standard push-in breather has, just the tube coming out the side and a solid bottom. i have a hose connected to the tube, and a PCV inline between the valve cover and the carb... seems to work, but i still get a little oil that seeps around the breather.

Originally Posted by joeybsyc

Does it matter if the PCV valve is actually "in" the valve cover? I have one of those "breather looking" push in deals with the tube out the side.. I call it this because although it looks like a breather, there are no holed in the bottom of it like a standard push-in breather has, just the tube coming out the side and a solid bottom. i have a hose connected to the tube, and a PCV inline between the valve cover and the carb... seems to work, but i still get a little oil that seeps around the breather.

No.

Here's mine sitting on top of an oil/air separator I made.
An SBC PVC fwiw, one of the performance models.

Look inside the PVC if you can, you'll see a number which correlates to the opening vacuum level.

The angle on the drain/return hose was changed so residual oil would drain back by gravity.

And a pic of a couple of the home-made fittings I made that go in the Buick's PVC grommet on the intake manifold.
The 90 degree model was used so the drain/return hose would run downhill.
The PCV in the pic with the fittings is a stock 455 Buick.

The straight one required the hose be curved and that sat it up too high fr proper drainback.

Originally Posted by C9x

No.
Look inside the PVC if you can, you'll see a number which correlates to the opening vacuum level.

Where should the PCV open in relation to idle vacuum?

That was good reading, thanks for the link. I think I have it working now.