Have done some homework,CONFUSED,Holley says to take vacume reading with a auto trans,in drive at idel,did that and got 15,,,they say Devide by 2,that would mean I want a 7.5 power valve,BUTT they say if vacume is over 13,leave the 6.5 in it,Holley tech guy knew less than me,and I know nothing.guzzi Mark

It's a race car...
Put a 10.5 into it, that will open the power circuit the soonest.

If the idle goes to hell and the exhaust fumes make you eyes water, back down to an 8.5
If it idles at 15 inches in gear, a 10.5 will be fine.
DD

surprised at lack of responses,I went ahead and figured it out myself,made a 9.78 power valve,works perfect,10.00 a little much,,,9.50 a titch too little,Fine tuneing,Guzzi Mark

Are you cutting the spring?

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Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

I would go lower in vacuum reading since you have a stall converter anyway. 8.5 for a motor like yours.

Lou

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Home of Slant6-powered fun machines since 1988

madmax,

I tried all you can reasonably use, from 4.5 to 10.5 and am now going to try a 2 stage. You ask why so few responses to your question, but I don't know and didn't see what kind of engine and what kind of vehicle, carb and so on you were asking re. application. Obviously Lou and DD know, but not me. I would gladly offer some experience if possibly relevant but don't like to take up bandwidth on prattle. My experiemtn is a pretty well built truck with a midwest convertor and 4bbl Holley, 3.91 suregrip and 727. Watcha got?

rock
'64d100

SORRY everyone,was kidding about power valve mods,I put a 8.5 one in it like Lou suggested,and after talking to Doc and Ceej,and Tristan,and putting a vac gauge in car,I came up with what I think was best,,,,,car is 2,660 with me in it,60 over motor Erson 280 cam 10.7 compression Holley 4160 64 primaries,68 secondaries,Car now feels like 400 hp.Going to dyno next week ,will be very happy with half that,I thank all that have helped me tru this,and am SORRY for posting some bull poop,Guzzi Mark

I rather enjoyed the bull poop....

Must be like my 10.487" Power valve.

CJ

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Part of Tyrde-Browne Racing

Errrr... I have re-adjusted Holley power valves.

Most of them have a threaded "valve stem" and round nut. (spring retainer) There is some loc-tite holding the nut so you have to break that loose with a little heat. (a soldering iron works well)

Once the nut is loose it is a "turn & try" deal, unless you make a special fixture and have an adjustable vacuum source.
The only time I mess with this is when I need a single stage PV that opens really early, like at 12 or 14 inches.
Be sure to re-loctite the nut once you finish your adjustment.

You can see different nut thicknesses and threaded stem sticking thru, in this photo. The spring trapped in between also comes in different rates.

In the end, it is much better to simply buy the rated PV you need.
DD

Doc,

Reason I didn't flinch at Madmax doing PV adjusting is I did some too!

When I was doing vacuum can calibration to make the tables I posted last year, it dawned on me that all I knew of the accuracy of the PV's was what Holley said. Not good enough for me because all I would end up with a a finely tuned can managing advance, but also depending on untested secondary dumps.

So I just continued with the Fisher lab vacuum pump and hand vacuum pump used with the cans. First I just brute force tore up a spare 6.5 to see how it worked, and found the faucet washer holding on the spring as in your pic and though it should unscrew. So I undid another and sure enough, variable PV! It was easy enough to get a range that I mentioned in this thread, the 4.5 to 12, by getting them used off ebay. I then simply mounted them one at a time into an aluminum plate drilled and tapped for the PV, epoxied a little clear 2 inch PVC pipe and cap over the valve onto the plate, glued a PVC nipple into the cap, and applied vacuum from the pump much as one could do with a hand vacuum apparatus. I wanted to know when the PV's opened and when they were fully open and if it mattered if vacuum hit fast or slow. (Like stomping on it or easing on it).

Those valves open pretty close to wide open regardless of fast of slow hits, and are darn close to the rated value, at least in my small sample. I was very surprised after all my recurving to find this, because everything in recurving is so variable (spring, can tension, etc.) I think the OV's might stay pretty constant for all normal use because I don't see anything that would really weaken the spring and it is in a cooling fluid with a heat sink for a mount. The reason I got interested last month in the 2 stages is I want to tear some up and see if we can make a 2 stage out of an existing one stage body.

rock
'64d100