Power Valve Choice

[moparsofcamelot]

Hey I'm stupid, can't help it. What exactly can I expect if I go from a 6.5 pv to a 5.5 on center carb of a 6 pack?
Thanks in advance.

[TheRamMan]

actually vacuum is what keeps the pv
closed.Until vacuum drops to or below
the amount specified by the spring in
the valve,at this point the spring can
overcome the diaphram and open the valve.
so a 5.5 should open later.heavy vehicles
(trucks)or aggressive camshafts (long over
lap)tend to like the "smaller" valves.
By the way NOBODY that drives mopars is
STUPID those people have other choices.

[This message has been edited by TheRamMan (edited November 10, 1999).]

[DartGT66]

A rule o thumb is, taht you should choose the power valve so that the vacuum rate is about 2 hgs lower than the vacuum of your intake at idle, on gear with an automatic.

[Bigdodgeram]

also remember that if the engine ever back fires there goes the power valve. you will need to replace it with a new one
good luck

[TD]

According the reference information I have for Holley carbs, you are supposed to connect a vacuum gage, then roll the car out a few feet and go to wide open throttle. Whatever value the vacuum gage drops to under full throttle, your suppose select a power valve rated 1" Hg. higher than the gauge reading.

[DartGT66]

TD, you couldn't be more wrong. If you have vacuum at WOT in the intake you have a too small carb. Your information is incorrect, and will result in pretty odd results. I have used Holleys for about twenty years in tens of different engines. I have experienced propably over thousand backfires, and have never lost a power valve. I know it can happen, but it isn't so common, more a myth. People buy a Holley and if it doesn't work properly they change the power valve without even knowing what the power valve does. Changing a working power valve to another working power valve doesn't usually solve their problems.

[Larry S.]

I have to agree with DartGT on the power valve issue. I had a built 340 in a 1970 Cuda, with a Holley 3310 on it. I never ran a choke on it so I did have a problem with backfire when it was cold. In the five years I had that car, I never had to replace the power valve in the Holley.

[TD]

The information I'm quoting is from a Petersen's publication about fuel systems. But I would like to ask you a couple of questions. What is the stock power valve value in a Holley 3310 carb? What do you think the vacuum reading in a stock 360 or 440 is with car in gear? Do you think that value is 8.5" Hg. or less?

[340king]

Ramman is correct on how the power valve functions. The power valve is for delivering additional fuel when the vacuum drops and the venturii have not added enough fuel for the conditions. If you have too low of an opening point on a power valve, you may experience a slight stumble before your PV opens. This usually only happens in a severe case. Engines require quite a bit of fuel during the opening of the plates and when they are wide open. That is the reason for the power valve. Last trip to the strip, I helped a guy from my home town with his Fiord between rounds (We only need to lift the hood on the Duster to cool it down between rounds, so I had some time). He was running a 3.5 PV and was having problems with the car missing. We changed to a 6.5 and went from 12.91 to 12.16 in two runs. There is always some vacuum in an engine, however small it is. He was closing the 3.5 PV on the top end!

[74CHARGER]

Well, I'm kinda new to all this but been having probs w/my 3310. According to A Holley tech they normally have a 6.5Hg P/V from factory. I have been hearing some different things to do to determine which P/v to use but I think Holley recomends driving at cruise speed w/vac guage hooked-up, from that reading select a P/V 2hg lower than that.(the other ways described for determining the proper valve I assume are correct, and due to trial/error and experience.) Hope you have more better luck with yours than I am.

[Larry S.]

Everything I've ever read on tuning Holleys said to check manifold vacuum at idle (tranny in gear if it's an automatic) then go two steps lower on the power valve. That has always worked for me.

[DartGT66]

TD, the 3310 is a 'universal' carb. It is ment to work out of the box in many different applications, and it usually does. However to really make it work well, you should check and propably change the power valve. Also the secondary spring is extra stiff out of the box to avoid bogging with any combo. You can usually change that in to a much lighter spring to make the secondaries open sooner, and really pick up some power. Extra tuning is needed with all universal carburators, if you want everything out of them. With the power valve, if the hg number is too low it doesn't usually mean alot for performance unless it closes in the big end like told earlier, the 6.5hg is a pretty safe number. But if the number is too high, meaning that your engine makes very low HG at idle, you can't make the engine idle properly and it's not good in normal traffic. In many race cars and in most secondary meter plates they use a 'blank' power valve.

[morpower]

ok my turn! s/a designs super tuning&modifing holly carburetors list# 3310 comes with a 6.5 power valve a .025 sqirter 72 jets. i've ran them for years and the first thing is get a strip kit p#37-921 it comes with power valves, sqirters, pump cams, gaskets, secondary springs,ect. example from the book in gear 15on vacuum gauge power valve should be a 13 to 13.5 i've found this to make things a little to rich so i would run a 12 to 12.5 the sqirters are to small a 28 or 31 gets rid of the hesitation the run either the pink pump cam in the #1 screw hole or the blue cam in the #2 hole depends on the vehicles weight. then change the secondary spring to the purple or the yellow spring again depending on the weight of the car. the book says 2 inches of mercury less the vehicle in gear (vacuum reading).hope this helps the strip kit has very good instructions to help make the 3310s run great can you say (new tires) the throttle response is great!!!!!!!!