327/300 carb CFM
 

Anybody know the CFM rating on that (AFB) carb ?

Re: 327/300 carb CFM
 

Mark, I am 99% sure it is 575 CFM....I was planning on putting a 300 HP in this Nova for SS/IA when finances (and too many cars) got in my way....LOL

Re: 327/300 carb CFM
 

Mark,

I was never sure of the rated CFM but it never seemed to be able to produce the extra 50 horsepower on the 327 that the General assigned it. On the other hand, if the 300 horsepower manifold had never been cast, where would the 283 cars have ever found that last 50?

c

Re: 327/300 carb CFM
 

Something else that should be "fixed".

Re: 327/300 carb CFM
 

Thanks...So it's 15 hp in a 65 Chevelle as of now ... roughly 180 lbs in J/SA over a 4GC..
I don't see it carrying that difference...Of course, without a dyno sheet.....???

Re: 327/300 carb CFM
 

Yes, I believe it IS 575 CFM. EXACTLY the same measurements as the dual 4 barrel carbs on a 409.

Re: 327/300 carb CFM
 

That carb wasn't the only difference between the 62-65 250 and 300 horse 327. A good question was brought up, but I'd like to know what the CFM rating of the 4 Jet carb that the 220 and 250 horse small blocks was. The intake difference was notable, and the 461 head as opposed to the 520 head was another factor. Is the factored horsepower really that great a difference?

Re: 327/300 carb CFM
 

and to that, Greg, part of the horsepower difference was in the upgrade to the 2 1/2" outlet exhaust manifolds on the 300 + up horsepower engines.. With headers on the engines, the performance difference was not as dramatic.
I believe the little 4GC ( 4 jet ) was around 450-475.

Re: 327/300 carb CFM
 

520 heads on 327 /250's was 64 and earlier.
65 327...Same exact specs except for carb.
My question has to do with how much real dyno hp and whether the AFB is worth the hp to offset the weight.

I had a friend who bought a 65 Impala, 4 speed ,327/250 new, and it came with single exhaust .
I doubt you would have seen a 327/300 that way...Ancient history though.
We're living in the Now !

Re: 327/300 carb CFM
 

Seems to me a 62-64 327 300 used the same 2 1/2' exhaust head pipe as the 409 340,380 and 409 horse engine. I didn't consider that because,like you said, discarding the stock exhaust for a pair of headers negated any differences in the OEM exhausts. The NHRA factored horsepower was 250 horse for the 62-64 327/250, and 265 for the 62-65 327 300 horse engine. Someone should give it a try! Imagine a 327 265 in a Nova.Might be fun, especially with a 3 speed automatic.Interestingly enough,the 65 250 horse had either a WCFB or a 4 jet with 461 heads. Horsepower rating was the same as the earlier engine with the 520's.

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.