Fevre

Sure there is some diff in the PCV used on eng with diff vac levels but I do not know how to determine what rating to use or if there is a chart showing diff ratings for PCV's. Any input/help is appreciated. BTW my eng produces about 15 to 17 at 900 rpm idle.

My69

Fevre:
Ive always wondered about this to. I am very interested in what you find out
Mike

lars

I'm pulling numbers and specs out of my tech library right now.... I'll post up when I have all the facts gathered...

467-Ratman

Lars, If you could post the number for me as well, my 454 runs 10 inches at idle. Thanks

lars

Looks like I'm coming up a little short on the info I'm actually looking for. I also just got off the phone with the engineers out at Echlin who do the PCV design. They actually don't have the numbers on the vacuum specs on each application: they duplicate the OEM parts, but don't document the vacuum spec.

The PCVs all flow the same (oriface sizing is the same). The difference from one PCV to the next is the weight of the checkball. The ball weight determines how much engine vacuum is required to unseat the ball and produce flow through the valve. A radical cam, obviously, needs a lighter ball than a mild factory cam in order to bleed air through the system at idle. Producing adequate flow at idle with a big cam will often preclude the necessity to drill the throttle plates on the carb to produce an acceptabe idle.

I'm going to test the unseat vacuum level on a bunch of different PCVs, starting with the PCV for the Grand National Buick (this appears to have a very light ball). I'll post up an article once I get the data compiled from this science project.

Fevre

Thanks again Lars

Did a Google search on it but could not find any ratings or guidelines. Wonder how many of us this affects, esp those who have switched to low vac cams, prolly not getting any ventilation at idle.

68shark

I have a couple of PCV's in the garage. When trying to eliminate a PCV/oil burning problem (later determined to be something else and fixed), I noted that not all pcv's seem to have the same tension, even though supposedly for the same application. The two I had were from different manufacturers. I have the XE 262 cam which would produce less vacuum than a more mild cam, say the L48 cam. However, the vacuum at idle pulls the pcv wide open, irrespective of the tension level of the two valves that I had. My conclusion was that the valves are essentially similar and so long as your engine produces decent vacuum, any valve that was designed as a replacement for the factory one should suffice. As Lars suggests, there may well be a noticeable difference with a radical cam.

Fevre

ttt

Surfer69

just bought pcv yesterday and says E on bottom but one in car has D on bottom. Just wondering if the difference is weight?

Fevre

That is what I am interested in, a ratings chart so you can select the correct one for your eng set up.