What Carburetor for Factory 4-bbl?

javelinjason wrote: Thanks again for all the input. We decided to get a Summit 500 CFM M08500VS and a 1/2" Summit brand phenolic spacer. It's a stock engine, so I feel this will be comparable to the Motorcraft 4300 which flows 431 CFM. This will be fun!

I think that the 4300 was 605 cfm, and everybody will say that the 500 is too small. My modified 360 for my AMX made 1 more horsepower (411) and 10 more ft/lbs of torque (426) with a 600 cfm Summit than it did with the same carb in 750 cfm.
I have a magazine that tested a high 500+ horsepower Chevy engine with everything from a 390 cfm carb up to a 950. There was very little difference between anything form 600 cfm on up. The 390 was 22 horsepower down at peak, which was about 6,000 rpm. I think the 500 would be fine with a stock engine.

For information the SAE AMC report rated the AMC AFB at 430 cfm, but this was at 1" hg test pressure or delta P. Todays industry standard for flowing a 4bbl carb is 1 1/2" hg. The conversion is the sq rt of the delta P, so the stock AFB would be rated at 527 cfm in todays world. I have had them all on the flowbench, and the 527 cfm rating makes sense.

Ken_Parkman wrote: For information the SAE AMC report rated the AMC AFB at 430 cfm, but this was at 1" hg test pressure or delta P. Todays industry standard for flowing a 4bbl carb is 1 1/2" hg. The conversion is the sq rt of the delta P, so the stock AFB would be rated at 527 cfm in todays world. I have had them all on the flowbench, and the 527 cfm rating makes sense.

Ken_Parkman wrote: The 4300 is a bit bigger carb than the AFB, and the 4350 is the same as the AFB. My flowbench cannot accurately flow a carb because you need a monster flowbench with a lot of power. But I can turn it to 100% and measure a pressure drop, and it is repeatable, so I can tell if a carb flows more or less than another. I've had 30 carbs across the bench so I have a good data base. The 4300 flows noticeably better than the AFB, just a tiny bit less than a 600 Edelbrock. BTW a 600 Edelbrock is a lot smaller than a 600 Holley 1850.

Doesn't Edelbrock and Holley use a different method of rating? Something like wet flow versus dry flow, and wet flow is less ?

purple72Gremlin wrote: Ken_Parkman wrote: The 4300 is a bit bigger carb than the AFB, and the 4350 is the same as the AFB. My flowbench cannot accurately flow a carb because you need a monster flowbench with a lot of power. But I can turn it to 100% and measure a pressure drop, and it is repeatable, so I can tell if a carb flows more or less than another. I've had 30 carbs across the bench so I have a good data base. The 4300 flows noticeably better than the AFB, just a tiny bit less than a 600 Edelbrock. BTW a 600 Edelbrock is a lot smaller than a 600 Holley 1850. And Ill believe you before I believe alot of other people.

I don't blame you. The only information that I have about the Autolite 4300 carb was from old magazines, and that info could be incorrect. I remember reading that it was 605 cfm in an article about AMC performance engines, and read more than once that it was a 600 cfm carb on the 351 Ford engines in 1970. It all depends on how it was rated, I guess. Somebody that has actually flowed one would know. I have one that came on my car that has been rebuilt by Pony Carbs before they ceased operations several years ago. I have it in a box, and not on my car.