Power Valve
Thread Starter
Intermediate
Joined: Oct 2002
Posts: 39
Likes: 0
From: McAllen TX
Power Valve
I recently changed carburetors, from an 850 holley VS to a Double pumper Barry Grant. I checked the power valve that came with the holley and the opening vacuum is 4.5Hg. This power valve seems way too small for an engine with a fairly mild hydraulic roller cam (duration 224 234 @ .050) It seems to me that an 8.5Hg is more adequate. My question is how can I make sure I'm using the correct power valve? :banghead:
Instructor
Joined: Nov 2001
Posts: 175
Likes: 0
From: St Louis MO
Re: Power Valve (duliz)
If you do not have a high overlap cam then you should choose a power valve that opens 2 in (hg) below your normal steady cruising speed vacuum reading. If radical cammed then you should select one that opens 2 in (hg) below the manifold vacuum at idle, ( in gear if an automatic). Hope this helps.
Race Director
Joined: Nov 2000
Posts: 11,872
Likes: 12
From: Waterloo ontario Canada
Re: Power Valve (duliz)
I agree with the other 2 guys. You want your power valve to open when passing or even going up a hill. If you can install even a temporary vacuum gage and get a power valve just a few points less then the running at a steady cruise speed for your combination. If you step even moderately heavier like going up a hill the vacuum should fall below the power vavle you choose.
