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Holley 4778 Question
I just picked up a 700 CFM (List 4778).
I'm going to rebuild it and could use some advise. Engine is a 428 with a max torque @ 4100 RPM and max horsepower @ 5300 RPM. With an efficiency of 90%, the 700 CFM seems right. Jets - 66 primary, 71 secondary Powervalve - 3.5 lb. (Manifold vacuum is 8lbs at idle) The carb has a 31 primary and 32 secondary squirters (Should they be 35-40 with the power/weight ratio?) What color accelerator pump cams should I start with? |
You really need to put it on the engine and try it, before you start making changes. Find out what the engine needs, then make your changes.
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Agreed to put it on the car and work from there. With 8 inches of manifold vacuum you should stick the original 6.5 power valve back in because it will need that for sure. I would install the original pink cam in position one. Discharge nozzle values seem high but again, once its on the car that's easy to dial back.
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I'd put it on as is.
8 inches at idle, rule of thumb is halve manifold vacuum at idle (8/2=4) then pick the next lower opening point. Which you have done at a 3.5 valve. I'd recommend Pink cams on both in position one, like most performance Double pumpers. Factory settings: 4778 has 66/71 mains, 25/32 pump nozzles. 4778-1 and -2 have 66/76 mains and 28/31 pump nozzles. |
You are at sea level. You will likely find that a power valve that is 2" lower than the average of what you see at idle and at medium cruise will suit you best.
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Sounds like some good advise!
I got it from a friend and it was de-tuned quite a bit. Just trying to get it back to factory settings. I found several websites giving me the factory jet size, just none that identified the squirters, thanks Gary! Also have had quite a few people tell me the 700 is too small. Holley and some of the other calculators say otherwise. I'll have to put it on and see I guess. Thanks again. |
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