what size power valve?specs added
#1862443
07/02/15 11:24 PM
07/02/15 11:24 PM
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Joined: Jan 2003
Posts: 1,365 elmira ny
hp340nos
OP
pro stock
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OP
pro stock
Joined: Jan 2003
Posts: 1,365
elmira ny
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vacumm in gear is 9 to 10 inches of vacuum.what size power valve to use.carb is an 850 aed db pumper on a 418 stroker small block solid roller cam,current pv is 3.5 or 4.5 have to open carb up to verify which one.
Last edited by hp340nos; 07/03/15 03:19 PM.
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Re: what size power valve?
[Re: hp340nos]
#1862512
07/03/15 12:30 AM
07/03/15 12:30 AM
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Joined: Jan 2003
Posts: 12,256 Benton, IL.
DaveRS23
Special needs idiot
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Special needs idiot
Joined: Jan 2003
Posts: 12,256
Benton, IL.
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Street car? If so, the cruise A/F and vacuum are the biggest pieces of the puzzle. DPs are typically very rich on the cruise and transitions and as such like a later opening PV than a more street oriented carb.
Do you know the A/F ratio and vac reading at cruise. Tranny and rear gear info would help, too.
Master, again and still
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Re: what size power valve?
[Re: hp340nos]
#1862590
07/03/15 02:32 AM
07/03/15 02:32 AM
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Joined: Feb 2011
Posts: 4,302 Nebraska
72Swinger
master
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master
Joined: Feb 2011
Posts: 4,302
Nebraska
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I have always had good luck with a 3.5 in the front and the rear blocked.
Mopar to the bone!!!
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Re: what size power valve?
[Re: hp340nos]
#1862604
07/03/15 03:08 AM
07/03/15 03:08 AM
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Joined: Jul 2004
Posts: 19,318 State of confusion
Thumperdart
I Live Here
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I Live Here
Joined: Jul 2004
Posts: 19,318
State of confusion
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I don't focus on idle vacuum but more cruise and go a bit below that so if you cruise at 10 inches of vacuum for example then a 7.5 or 8.5 should be close BUT you need to experiment to adjust how fast you need the enrichment to suit your needs.
72 Dart 470 n/a BB stroker street car `THUMPER`...Check me out on FB Dominic Thumper for videos and lots of carb pics......760-900-3895.....
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Re: what size power valve?
[Re: 72Swinger]
#1862703
07/03/15 10:47 AM
07/03/15 10:47 AM
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Joined: Oct 2003
Posts: 11,686 W. Kentucky
justinp61
I Live Here
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I Live Here
Joined: Oct 2003
Posts: 11,686
W. Kentucky
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I have always had good luck with a 3.5 in the front and the rear blocked. I used to run a 3.5" too and thought I was doing good, had always been told to run a PV that was 1" less than my idle vacuum. After several phone conversations with Dom he finally got it through my thick head that idle vacuum had nothing to do with it. I now have a 6.5 in it now and my LM2 recordings look better.
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Re: what size power valve?
[Re: hp340nos]
#1862756
07/03/15 12:15 PM
07/03/15 12:15 PM
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Joined: Oct 2007
Posts: 4,210 New York
polyspheric
master
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master
Joined: Oct 2007
Posts: 4,210
New York
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Re: what size power valve
Just to clarify: power valves don't have sizes, those numbers are vacuum levels. The "size" is not in the valve, but in the carburetor body, it's the PVCR (power valve channel restriction) and without going to aftermarket the adjuster is a drill.
Boffin Emeritus
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Re: what size power valve?
[Re: Crizila]
#1862836
07/03/15 02:21 PM
07/03/15 02:21 PM
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Joined: Jul 2004
Posts: 19,318 State of confusion
Thumperdart
I Live Here
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I Live Here
Joined: Jul 2004
Posts: 19,318
State of confusion
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I might add that all PV's aren't the same. Many aren't even close to what is stamped on them - especially those that come with a new carb kit. Most accurate ones I have found come from Quick Fuel. They only sell the 4-door Hi-flow valves. So true and I only use quickfuel 4 Window pvs now which flow more fuel and allow more precise tuning of the pvcrs.
72 Dart 470 n/a BB stroker street car `THUMPER`...Check me out on FB Dominic Thumper for videos and lots of carb pics......760-900-3895.....
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Re: what size power valve?
[Re: AndyF]
#1863209
07/04/15 12:41 AM
07/04/15 12:41 AM
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Joined: Jan 2003
Posts: 12,256 Benton, IL.
DaveRS23
Special needs idiot
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Special needs idiot
Joined: Jan 2003
Posts: 12,256
Benton, IL.
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If you drive it on the street a fair amount then you want to set the power valve so that it comes on at about 1/2 the cruise vacuum level. So for you something in the 7,8 or 10 range should work for you since you cruise at 15 inches.
But if you drag race the truck then you want to make sure that the PV is open when you need it to be. A 8 should work just fine but you really need to double check the vacuum during a run to see where it is. Going down the track you should be at WOT and the PV should be open the entire time, but at the starting line it may or may not be open depending if you foot brake or not.
Vacuum at idle shouldn't really matter for PV selection. If having the PV open at idle causes a problem then you have other issues with your carb. I agree with Andy's answer. The only thing I would add is that IF you had a WBO2, the best way to set the PV opening is just before the lean spike happens. And the cleaner (leaner) your car (truck) cruises, the sooner that happens so the sooner the PV needs to open to compensate. If however, your carb is rich in the transitions and cruise, that earlier opening point is giving it more fuel than it really needs or wants. But most guys do not put that fine a point on it. If you have to guess, then you are better off with an earlier than needed opening rather than a later than needed opening. Our engines are much more tolerant of overly rich conditions than they are of even slightly lean conditions. So, if in doubt and without any A/F info, there is less chance of a problem with the earlier opening. If you are experiencing no driving problems on the street with the PV you have, making a change will probably not help anything. But at the track, changing to an earlier or later opening may impact the 60'. Only testing will tell.
Master, again and still
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Re: what size power valve?
[Re: Thumperdart]
#1863323
07/04/15 09:11 AM
07/04/15 09:11 AM
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Joined: Mar 2009
Posts: 2,470 Sydney,Australia
tex013
top fuel
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top fuel
Joined: Mar 2009
Posts: 2,470
Sydney,Australia
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I don't focus on idle vacuum but more cruise and go a bit below that so if you cruise at 10 inches of vacuum for example then a 7.5 or 8.5 should be close BUT you need to experiment to adjust how fast you need the enrichment to suit your needs. I am with Dom on this .its load dependant , if you are running a high stall it will affect choice as well .i have about 4" @idle but i use a 6.5 QF pv to get drivability and tip in correct . I have a 5000 stall vert Tex
New best ET 10.259@129.65 . New best MPH 130.32 Finally fitted a solid cam, stepped it up a bit more 3690lbs through the mufflers New World block 3780lbs 10.278@130.80 . Wowser 10.253@130.24 footbraking from 1500rpm Power by Tex's Automotive
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