Crankcase breather question

Well, I just know a few. They variations are:

• The vacuum level at which the PCV valve transitions from low suction (idle) mode to high suction mode
• The size of any restriction inside the PCV.

The pricey ones allow you to adjust both in the same unit. But you can find ones that have varying transition vacuum levels. That is the most important thing for most of the engines here.

The stock Mopar PCV transitions from low to high suction mode at around 14" of vacuum. But a lot of cams are idling with less vacuum than that. So the stock Mopar PCV will be wide open at idle with a moderate cam and letting too much air into the intake and making idle and transition tuning difficult.

So the objective is to find a PCV that transitions from low to high flow at a vacuum level below your engine's idle vacuum. MP makes one (can't recall the number) and we used a Fram FV191 IIRC, which is a GM one for performance V8's in the 70's-80's. (But you have to change your valve cover grommet size for that one.) There are a few PCV valve threads here that, if you search for them will give more info.

If you want to limit the PCV flow then a simple restrictor in the hose works. But I have not seen the need for that so far. I mess with 70's Opel and the 'factory PCV' was simply a small restriction in a hose nipple.

And BTW, at WOT there is no 'shut-off' of the PCV that I am aware of.... it just stops flowing much simply because it does not have the vacuum drop in the intake to be effective.