[NYGTO]

Hi gents, my understanding is that the AFB used on the early GTO's would flown around 550 CFM.

My question is, what other CFM sizes did the early AFB's come in? Were they installed on Cadillac and big block Chevrolet?

I'm wodering what might be a good, larger replacement. I'd like to test this out and see how it compares to a tri-power set up.

Thanks!

[Cardo]

From what I've read they're 585 cfm with the hot idle compensator and 600 without. Carbking would be the one who knows. You may be able to find out more on his website. I don't know if there's much to be gained by going bigger on a stockish engine, as the 65 with a tri-power was only rated at 25 more HP, but a few lbs less torque.

[tom s]

Some of the hi po AFBs we’re up around 750.400 HP single 4 4o9s were like that.Max Wedge Mopars up there.421 SD NASCAR single4s up there.All of the mentioned carbs are 5 inch top AFBs.Tom

[Kenth]

This might clear some fog. Thank you, Jon.

https://www.thecarburetorshop.com/AFB_flow_ratings.htm

[NYGTO]

Thanks guys, Ill look into this more. Maybe a 409 afb is possble. Many years ago I kept adding jet size and cfm to a 360 Dodge and everytime resulted in better performance. I keep beleiving that the base afb is a major resrriction even on a stock engine.

[tom s]

3705 Mopars are great 750s.Maybe a little pricey if you find them.Tom

[NYGTO]

Thanks Tom, that would be something like I'm talking about. A straightforward AFB swap just to personally see the performance difference between small and large afbs'. This all came about from a discussion Iwas having with well versed Pontiac friends explaining that Pontiac kept the smaller afb on the GTO for a few reason's and the stock 335hp was much more capable. Almost like the smaller afb used was a safety feature against engine damage and warranties being used.
Or even making the 3 x 2 cars look not that much quicker over the single 4bbl.

The experiment is all in fun.

[scott06]

Originally Posted by NYGTO

Thanks Tom, that would be something like I'm talking about. A straightforward AFB swap just to personally see the performance difference between small and large afbs'. This all came about from a discussion Iwas having with well versed Pontiac friends explaining that Pontiac kept the smaller afb on the GTO for a few reason's and the stock 335hp was much more capable. Almost like the smaller afb used was a safety feature against engine damage and warranties being used.
Or even making the 3 x 2 cars look not that much quicker over the single 4bbl.

The experiment is all in fun.

A edelbrock 1406 is essentially an AFB- 600 cfm. You may be limited by the stock intake. If you have an original 500 cfm would be interested to see at WOT what the vacuum is in the intake stream, that would tell you if you need a bigger carb.

I had a 1406 on my 65 389 (stock) ran very well. I did swap it out for a tripower, but the idle was better with the Eddy. Also swapped cams at same time (067=> SPotts 068 HL) so not sure how much is from the carbs and how much from the cam

[Gulfstream64Post]

If I have the stock 1964 4-barrel air cleaner housing can I use it with a newer 600 or 750 Edelbrock by swapping to a different bottom piece/base? Anybody know of any aftermarket bottom half that would combine with the stock upper half?

[WQ59B]

Originally Posted by Cardo

From what I've read they're 585 cfm with the hot idle compensator and 600 without. Carbking would be the one who knows. You may be able to find out more on his website. I don't know if there's much to be gained by going bigger on a stockish engine, as the 65 with a tri-power was only rated at 25 more HP, but a few lbs less torque.

Circa 585 is where my '64 AFB / auto spec'd at.
When I ran the carb numbers on my '64 Tri-P set ('64 center / '63 outers), it came to 883.

[Cardo]

^^^ So based on the Tri-Power CFM numbers, adding more CFM availability to a STOCK engine, will probably not add to the performance. Cam and headwork would required in this situation. When I built my 389, I had the heads ported and flowed, and a slightly larger cam. It made 400 hp and 460 ft lbs of torque on the engine dyno with the factory 585 cfm AFB with the hot idle compensator installed. That being said, I really don't see the need for a bigger carb in a stockish situation being that it seems to me we haven't "used the stock sized one all the way up".