Fram FV181 for a 1966 Corvette 427 ci has pintle up with only 10.5-11 inches of vacuum at idle.

Started my son's hot 351w Ford to break-in cam this weekend and tried this one on a guess as I was worried low vacuum would have any low performance stock PCV open at idle. This one was snapped tight, opening flow while driving under load is yet to be determined.

Thought I would pass this along as it was one of my worries and found differing opinions on what to use.

 

Coronet -

My 440 runs about that vacuum and has for 30 years.
Never did any flow rate checks, but the engine has been fine with no signs of crankcase pressure. Stock PCV too.

Archer

 

I have used these before and they work great.......

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

 

I am totally confused. I had no idea that this could be a problem or even need to be checked. How much vacum is supposed to pull at idle then at crusing speed?

 

A stock engine will have 18-21 inches of manifold vacuum pulling the pintle to restrict the valve at idle, small amount of blowby at idle, small amount drawn into intake manifold.

When your cruising vacuum may be in the 8-10 range allowing the valve to open more and draw more crankcase gases (blowby) that is created with the higher rpm.

If you have a performance cam with low vacuum at idle the pcv valve may be more open than desired, which can create idle mixture tuning difficulty.

The one I chose was a guess at an OEM engine with a big performance cam. I've now found out this is also recommended for a Ford Boss 302, probably any manufacturers top performance engine would have this allowed for in their design.