I have a 71 GS 455, 70 heads w stage 1 valves ported, ta 290-08 H around 10-1 cr, performer intake ported w back half cut out, msd ignition, 3500 stall 3;73 gears 28" mt-et's racing at 800' sea level. The car runs low 12's I want in the 11's, after years of harassment I'm taking off the Q-jet, and borrowed my brotherinlaws holly preform 950 from a 383 sb that ran high 10's, he said he would run it as is w #92@#77 jets and read the plugs but a mud dauber made a nest in it so it hasta come apart anyway. I'm going to mo-kan Friday night and thought any of you w Holly experience could give me a better starting point. I'm new to hollys and would appreciate any advice.
I'm assuming the 92's are in the secondaries with no power valve and the 77's are in the primaries with a power valve. Thats too big a spread. typically a power valve is worth 6 jet sizes. Also,the power valve designation is important, it refers to at what vacuum the power valve opens to give this extra jet sizes. With your combo I'd try a 4.5 or 5.5 power valve in the primary with 82 jets and 88 jets in secondary with no power valve. You could check vacuum by using a vacuum gauge to rear of carb, then use a power valve 2 numbers less. eg. if you read 8 inches of vacuum at idle use a 5,5 power valve, if 9 inches at idle I'd use a 6.6 power valve. Of course my suggestion is probably close but each app is going to be different and plug reading should be done to verify too rich or lean. gary
Thanks, I had to look up what a power valve is.His engine had a roller cam and pulled good vacuum,mine is lucky to pull 8''. I'm guessing on the jet sizes #92 & #77 that are missing from the jet kit. I guess it came w #73P since there are 4 each in those slots. Really appreciate the advice. With your knowledge and a borrowed holly hopefully I can show Joplin a Buick w a vinal top, bench seat and coloum shifter that runs 11's. TKS
I ran a 950 prosystems carb on our 464 11.5:1 motor. We ran 86 up front with 's 1.5 pv and 94 in rear. Car ran 11.0s and 10.90s. Our 308s only pulled like 5 inches at idle. We had 50cc pumps but smaller squirter to draw the pump shot out longer. I always hear ppl talking about changing the power valve to help with idle.....it has nothing to do with the idle circuit. It only helps man metering.......if your pump shot is too big delaying enrichment with keep it from going rich when your have both pump and main metering going at the same time. I personally think that carb is a little to big for your combo, when we ran low 12 high 11s we used a 750 edy and then an 800 holley dp
I'll try to dig out my notebook on when i spent bookoo time tuning my 950 Holley. I kept detailed notes on jets, powervalves, squirters, cams, everything. It's a tad rich now (hovers around 13 on the AFR gauge) but it runs great so I've left it be since I'm not et hunting. Might give a decent reference point for you though. And I'd definitely take what Mr. Paine has to say to heart, he's been dialing in carbs longer than I've been alive...
I took it apart at work today it had #77@#92 w a 45 stamped in the power valve I guess its a 4.5 I put in the #82front #88 rear. the metering blocks were stuck bad, I don't think the reusable gaskets are still reusable. got new gaskets at lunch, the mud daubers had just filled the primary air tube. Should have it together tonight. I figured a 950 was to big but I took it off my brotherinlaws car on fathersday (his engine is blown and he bought land and is building a house) Last time I tried a Holly 830 I lost e.t. but gained a lot in mph never tuned it just borrowed it for a weekend. Ive always been a Q-Jet guy . I have a feeling the accelerator pumps are to big and who knows on the pump cams. His engine pulled 16'' vaccume and had a 4.5 power valve but the idle screws were only turned out 1/4 turn. I guess ill see what it does if it shows promise ill keep tuning, if not I'm putting the Q jet back on. THANKS for the advice I'm feeling better about my base tune.
Spray all Carb gaskets with WD40 and they'll just fall off when you service it.... Mr Jim Rogers showed me that tip good many years ago
Thanks for the wd40 tip. I would like to see Shawns notebook , but I am taking Mr. Paine's advice. I'm new to the forum but I couldn't believe the guy w Thumper answered me. I dig the Rusty Hulk I have a green 70 Skylark post I have been thinking about putting all the go fast parts off my GS on it and guting it. and put in my old 455 w 430 heads KB118 cam @ stinger ignition and putting the AC back in the GS. My GS is my first car bought it in 83 when I was 15, dated my wife in it, she hates me racing it. I do have enough insurance to replace it if I wreck it but it wouldn't me my car. I live south of K.C. Mo. they closed KCIR 8yrs ago so now I just go to Topeka Ks or Joplin Mo. to tune and would be more at ease on the streets w the Skylark. Thanks Again
