i have a 1968 mustang and it has a holly 600 vacuum secondary carb on it with a edelbrock performer intake on a 302. my dads buddy has a 502 shevy in his 1948 ford business mans coupe. he had a jetted up 750 holly on it and it was a dog, it always ran rich and had not the power he should have had. he traded the 750 fer a 650 edelbrock thunder AVS and it totally woke the car up, now it hauls. my dad has the same car with a 350 chev, same intake as me and a GMPP ZZ4 cam in it. he has the 600 edelbrock on his. my question in is my engine over carburated? would it be snappier if i had like and edelbrock 500 on mine. i have 3.73 gears and a c4. remember im lookin for street performance

 

At 5250 rpm a 302 engine will flow 459 cfm assuming 100% volumetric efficiency.In the olden days we always overcarbed our engines.More was always better,right?Too big of a carb causes velocity to fall off at high rpm's and the mixture goes haywire.I would try the smaller carb myself.The formula to figure CFM is 1 cubic foot =1,728 ci. 302/1728=0.1748 0.1748X5250=917.7 Since the engine only inhales every other cycle,divide 917.7/2=458.85

 

A 600 CFM carb on a 302 Ford should be a pretty good fit. Same for a 750 CFM on your buddies big block chevy. Just make sure the jetting is set up right.

A buddy back in highschool had a real nice done up '74 Trans Am with a 455 bigblock. He stuck a singleplane Edelbrock intake & a 780 Holley on top, and along with the Crane 3/4 cam, big tube headers, and 10:1 compression, that thing hauled serious ****. Only got about 6mpg, but who da hell cares about that?

 

I agree a 600 vac. carb should be a good fit for your 302, it does need to be tuned properly, which is somthing that 95% of the people don't right. Just to let you know "jetting" up a carb will just make it very rich, everything depends on the A/F ratio. Most likely on the 502 you mentioned, the motor was pulling alot of fuel threough the jets because of its size, making it run rich.

 

Back whenn Ford built carbed motors they used a bunch of 600CFM Holleys on 302 and even 289's.
If the carb is working right it should be fine.
The 'jetted up' Chevy was probably jetted too rich(fat). Jetting will make no differance in airflow as you can't jet airflow, only fuel flow....