Power Valve #'s

[finnman1]

I understand dividing vacuum by 2 and adding a point to get the magic #, but the p.v.'s are marked as E 3 5 6, and E 8 5 0, and # 8 5 8. Three #'s, not two. It seems the Higher the #, the more pressure it takes to close the p.v. w/ your fingers, the one i have in the primary side now is even weaker, so i presume it would be a E 1 4 8 or something like that. Maybe my vacuum gauge is broke or something, but in gear at idle, i'm measuring about 6hg... the cam lumps like a sonofa though. (mystery cam) 3.5 = ?; the E 3 5 6? the plugs are reading way too rich city driving around. i imagine the weak spring rate pv in there now is letting too much gas in?

The real question is, if i need a pv rated for 3.5, how do i identify which one i should use via the #'s stamped on it. Would i use the E 3 5 6? Is that the closest one to a 3.5?

 

[ramcharger]

The only time I've seen power valves marked as per your example is if they were original equipment at one time. It sounds as though the selection of valves that you have may be from a bunch of different used OE Holley or Motorcraft carbs. I would suggest buying the correct one for your application rather than playing "hit or miss" with a selection of used valves, as the used ones may be blown from a backfire.

Here's link to Holley's power valve selection guide: http://www.holley.com/data/TechService/Technical/power_valves.pdf

Good luck!

 

[dgc333]

The ones I have purchased when looking at the diaphragm side sometimes have a letter and a number in the 9 o'clock position but at the 3 o'clock position there is two numbers stacked.

6
5

These are the rating at which the valve opens.

 

[moper]

Yeah, you're looking at the date codes stamped on them, and the opening rate numbers. IN terms of the design...I've heard a bunch of things, even two seperate things from Holley people themselves via phone. From what I have picked up, the rating is the amount of vaccum required to keep the valve fully seated (closed). Most engines will be fine going by that "1/2 the vaccum reading in gear at hot idle" bit. But, some packages will run better with variations of that. The stiffer the spring, the more vaccum it needs to stay shut, and the sooner (in terms of load being applied) they will open.