600 vs 800 cfm - Pontiac GTO Forum
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post #1 of 23 (permalink) Old 05-26-2011, 07:41 PM Thread Starter
 
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600 vs 800 cfm

According to the how to build pontiac V8's book by Jim hand the 455 motors should run a 800 cfm carb. I currently have a 600 that I am contemplating rebuilding. Should I scrap the rebuild and get an 800 or can I run a 600cfm on my 455. Any thought ?

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post #2 of 23 (permalink) Old 05-26-2011, 08:51 PM
 
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Personally, I wouldn't run a 650 on a 455....nothing less than a 750. If Jim hand says 800, then run an 800 ! Eric



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post #3 of 23 (permalink) Old 05-26-2011, 09:11 PM Thread Starter
 
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Thanks, I think that is what i am going to do

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post #4 of 23 (permalink) Old 05-27-2011, 07:28 AM
 
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We use AED's 850 HO" carb for street builds. Reasonably priced and makes big power
"right out of the box".

FWIW

Jim
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post #5 of 23 (permalink) Old 05-27-2011, 09:01 AM
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A 600 would be right for a 326 or a 350. Even the 400's had 750's...a tripower is something like 1000cfm, and it came on little 389s.
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post #6 of 23 (permalink) Old 05-27-2011, 09:18 AM
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Except for the super duties and HOs, even 455s had 750s until '75. Then 800s were on everything, including 350s and 301s..



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post #7 of 23 (permalink) Old 05-27-2011, 09:42 AM
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with previous comments. 600 isn't going to 'git er done' even on a mild 455. It'd be like trying to run a marathon while breathing through a soda straw.

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post #8 of 23 (permalink) Old 05-27-2011, 08:31 PM Thread Starter
 
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Thanks so much for all the great info. I have been having to add gas to my 600 carb in order to get the car to start when cold. Thinking that not enough gas was getting to the carb i was figuring that a rebuild was necessary. So this is good news, now I get to throw a bigger carb on it and get more power at the same time.

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post #9 of 23 (permalink) Old 05-27-2011, 08:39 PM
 
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lots of big engines also run 2 barrels and start fine if they are tuned right.


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post #10 of 23 (permalink) Old 05-28-2011, 02:38 PM
 
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Quote:
Originally Posted by SDGoat619 View Post
Thanks so much for all the great info. I have been having to add gas to my 600 carb in order to get the car to start when cold. Thinking that not enough gas was getting to the carb i was figuring that a rebuild was necessary. So this is good news, now I get to throw a bigger carb on it and get more power at the same time.
That symptom is something else entirely. The float bowls are leaking down, or the fuel is siphoning back to the tank. It could also b a problem with the choke if you only need to do that when its cold. You might have the same problem with a bigger carb and that would point to the fuel system. A bigger carb on a 455 wont hurt though. I still like Qjets, but Holleys work quite well, I ran them on 455s for years. I didnt see much difference between a 750 Holley and an 850 on my low compression 455s, but they will handle it. Any Qjet will work for a mild street engine with the right configuration.
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