Re: 327/300 carb CFM
 

4 GC is 245...
AFB is 260 in a 65 Chevelle ..

Might be fun with a T200 ..but it's a lot cheaper to find out on a dyno...in the long run.

Re: 327/300 carb CFM
 

Going in memory, the 327 with 250 hp had the 283 cylinder heads with a 1.75 int valve and a 1.5 exh ,small intake with a 4GC car and small exhaust pipe. The 300hp had the double hump heads with 1.94 intake valve with 1.5 exh with a larger intake manifold with the AFB with larger exhaust manifold. I started going thru some dyno sheets where I pulled the 250 intake and carb and installed a AFB and int. I think we picked up some hp but the heads were a restriction. Some of you guys will probably remember more than I do
reed

Re: 327/300 carb CFM
 

Not sure on the AFB carb...but checked into the 4GC's cfm rating many years ago...

Think I found about 475 cfm for the smaller early carb..(circa '57-'60?)...

Thought that the later carb was about 525...on the 220 and 250 hp engines...

Think there's one other 4GC as well...but that doesn't apply here....

Talking Chevrolet ONLY here...other GM's might be different....

Re: 327/300 carb CFM
 

My Corvette is able to run both combinations and we found that the AFB is 2 tenths faster than our WCFB with the right tune up. No dyno time just track tested.
Tony Hernandez

Re: 327/300 carb CFM
 

Not sure of the carb specs that is being used with that particular combo but the smallest AFB is rated @400 CFM and they go up in size to 750 CFM while a WCFB is kinda rated @ 385 CFM for the smallest ones--- Found this a long time ago not sure how accurate it still is

AFB Carbs
CFM Venturi Diameter Bore Diameter
Primary Secondary Primary Secondary

400 1 1/8 1 1/4 1 7/16 1 7/16

500 1 3/16 1 1/4 1 7/16 1 11/16

575 1 1/4 1 9/16 1 9/16 1 11/16

625 1 3/16 1 9/16 1 7/16 1 11/16

750 1 7/16 1 9/16 1 11/16 1 11/16

ALL AVS CARBS

Primary & Secondary same size 750 CFM
Primary & Secondary different size 630 CFM

4GC CARBS

CFM Venturi Diameter Bore Diameter
Primary Secondary Primary Secondary

486 1 1/8 1 1/4 1 7/16 1 7/16

553 1 1/8 1 15/32 1 7/16 1 11/16

692 1 1/8 1 15/32 1 9/16 1 11/16

Re: 327/300 carb CFM
 

Except '65; the 327-250 used the same heads as the 327-300 in 1965. Been that way as long as I remember.

Re: 327/300 carb CFM
 

That is correct..
In 64 and 65 the 327 were both rated at 250hp.

D

Re: 327/300 carb CFM
 

Mark, Cupp has answers to all those questions. Dyno comparisons, on track back to back, every trans. and rear gear combination you can think of. We have MIR again on Monday and he will be beating the tar out of the green bean again. ------ I'm going to quit parking beside him----------Danny :)

Re: 327/300 carb CFM
 

Seems to me that the 409 340 horse engine of 1963-65 had a BIG 4 jet on it. 394 Olds motors and the big Buicks got it as well. Heard of a fellow putting one on a 283-220 horse and getting a BIG quantum jump in horsepower with it. I had a 65 Impala SS convertible with a 409 340 horse and a 4 speed, but I ran an AFB on it,since they were easier to maintain. That car was a real road monster with the 3.31 gears, and it would tow about anything. Nothing like torque.