Proform 950 main body swap

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J

Johnny from Chicago

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Anyone tried using the Proform 950 body on an 850dp (4781)? The tech line for them said that they use the same baseplate but the 950 holley has 1 11/16 bore and the 850 has 1 3/4. Wont the 850 make more power no matter what they call it - bigger is better isnt it? I got the 950 body and set it on the plate and it is 16th smaller. Doesnt hit the blades when they open. Should I run it, will it perform better?
 
OK, here's my take on this question.

Holley designed the 950 carb body with a venturi diameter a certain percentage smaller than the throttle bores to ensure that the boosters and main jet orfices see a certain amount of vacuum to ensure that fuel gets pulled in in the correct ratio. A different size throttle bore would upset that ratio (by how much, I don't know) and may cause fuel delivery and atomization problems, plus a small dead spot below the "step".

That could lead to weird off idle problems as the idle transfer slot would be directly below this dead spot, but I've never tried this type of modification.

The only way to know for sure before you bolted this on would be to wet flow the carb modified in the manner you describe.

Good luck! :)
 
Where do you go to get a carb wet flowed? Am I just jerking myself around playing with these bodies, or should I just buy a bad -*** new carb. I read alot about everyone needing more carb, but I've got a stock eliminator friend who thinks my 440 is overcarbed with an old 4781 850 because his breathed on 780 ($700) goes 10.31 in his Fairlane. I just know that my car ran ok with a vacuum secondary 750, but was an animal when I put the 850 on. It developed a popping on accel issue, so now I'm thinking of stepping up.
 
446 with stock edelbrocks, m1 intake 13:1 compression with forged Ross pistons, steel crank, H-beams, 1/2 inch studs in main bearings, Crane roller 630 lift with 268 & 278 at .050 duration. 3400lb 70 Dart with me in it, 456 gear, Pro-trans with 3500 converter, leaving on the footbrake from 2000 with a lean hesitation(dont have the squirters dialed yet) and the 850 carb It goes 7.25 at 98 in the eighth. Never got a totally clean pass off the line. I'm going to try a two-step for the leave next week.(I will be sending the heads to Modern for the Max Wedge port job in the near future)
 
I think you would pick up a 10th or two with a 950, but I'd get the 950 right from Quick Fuel or Holley.
 
I read several places now that the 950 holley isnt really a 950, that its more like an 830. It does have smaller venturis and bore than an 850 according to the holley manual I have. They say that it is flowed differently and it rating is more optimistic? I was thinking of jumping ahead of the questionable 950 and getting a QFT 1050 annular. Thoughts? It's a drag only car, and I actually need to open up the exhaust - its running through full system 3" with 3 chamber flowmasters and Pro-part headers.
 
If it's strip only, I'd say go for it. Socal has a good point too. I've called QFT and they've been very helpful. Let us know what they say.
 
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