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Old 01-02-2009, 10:45 AM
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need carb advice

I need some advice on what carb to use with my now completed 350 top end rebuild. Heres what I have:

- 350 4-bolt, 1976 with stock pistons and crank
- comp cam xtreme energy 274 cam, 490 lift intake and
exhaust, tappet lift 274
- edelbrock performer manifold
- completely rebuilt heads- 60cc, 2.02 intake, 1.60 exhaust
- on the rebuild, new high performance oil pump, fuel pump
(mech), water pump, radiator, gaskets, seal, etc.
- rebuilt saginaw 4-speed
- electronic ignition
- time set at 10 degrees btdc
- engine is in my 1966 chevelle
A friend is recommending 750cfm. Another friend says thats too much carb, and that 600 or 650 cfm if plenty. Whats the correct answer ??

Any help will be appreciated.

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Old 01-02-2009, 10:53 AM
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Another friend says thats too much carb, and that 600 or 650 cfm if plenty.
Ayuh,... I completely Agree...
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Old 01-02-2009, 11:09 AM
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There is alot of posts on this subject and you could do a search and read more on this subject. Carbs are tough! There are so many styles, brands, CFM, vacuum secondaries, double pump, you name it. I'll give you my opinion for what its worth and I'm sure others will disagree. I prefer Holleys. They perform well as far as performance go. I've run Edelbrocks and they are reliable but don't count getting that kick in the rear feel when you step on the pedal. CFM- There are calculators that will determine what CFM range you should be running. With a 350, according to the calculator, a 600 CFM carb would be good. I like running bigger CFM carbs. I'm running a 650 CFM double pumper on my Ford 289. People all tell me, your way over carburatored for that engine. I'm not running rich and the car comes unglued with this carb. I've run a 500 cfm and 600 cfm and it's like putting a 2 barrel carb on. With what you got, I'd go with a bigger cfm carb. The 750 might be a bit big for your engine, but a 650 like I'm running might do the trick
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Old 01-02-2009, 01:20 PM
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why do some people start from the crank and build up, wouldnt be wiser to start with what you plan on for carb size etc first.... dam i wouldn't build a motor with 12.5.1 and expect to put a 671 blower setup on it gee *** did i do wrong

Last edited by smrat; 01-02-2009 at 05:24 PM.
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Old 01-02-2009, 02:20 PM
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Quote:
Originally Posted by jjpodlas
. Whats the correct answer ??
There is no correct answer because you told us what you have but you havent told us what you WANT..

Are you all about balls to the wall power and nothng else? Get a holley 750 or similar. It can be made to work just fine. Are you more inclined to want a combination of mileage and performance? If so lots of carbs will work. Do you want the best mileage you can get first and power second? Quadraqjets are great for that and I personally like a 600 cfm edlebrock for that as well.

Any of those cabs can be "made to work" on your motor. But you will find that a 600-650 cfm will be closer to a bolt on and go proposition for a basic 350.

Selecting a real good carb for your application also is NOT just about CFM's. There is a lot more to it than that. Sometimes a good place to start is how much do you want to spend and how much tuning are you wiling to do?

Last edited by 65smallblock; 01-02-2009 at 02:28 PM.
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Old 01-03-2009, 06:29 AM
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I had a 350 with a 268 comp cam edelbrock performer intake headers. I first put on a 1850 600 vac sec holley it ran good. Then I put on a 3310 750 vac sec holley and it ran really good. It was in a 76 monte with 410 gears and a posi. smoke the tires at will. If i were you go with 3310 750 holley. the secondaries only open with the engine wants it......i miss that car
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Old 01-03-2009, 07:36 AM
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The 750cfm Holley will work fine as long as it is vac secondaries. Where people over do is when they put on a 750cfm double pumper for street use. You can tune the vac secondaries on the Holley to open any time you want them to, and it is a lot easier than a Quadrajet. You might consider the 750 Street Avenger Holley.

Vince
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Old 01-03-2009, 08:41 AM
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do some reading in the "Knowledge Base" link at the top of this page for articles under the engine/carb section like this one for total cfm thru the motor versus rpms and cubes....

http://www.arnolt.com/Bitmaps/Articl...rafbtuning.pdf

there's also a Holley article chart to compare against....

CRS=your cam HP peak is 5900 rpms??? (for total flow needed)
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Old 01-03-2009, 09:53 AM
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Quote:
Originally Posted by 302 Z28
The 750cfm Holley will work fine as long as it is vac secondaries. Where people over do is when they put on a 750cfm double pumper for street use. You can tune the vac secondaries on the Holley to open any time you want them to, and it is a lot easier than a Quadrajet. You might consider the 750 Street Avenger Holley.

Vince
I'm running a 650 DP on my car and will always have double pumpers. I got tired of replacing those stupid O rings on the fuel tubes that go into the fuel bowls. They always leak. I always had problems with the secondary diaphragm not working because it got dried out or had a rip in it and needed replacing. It's my understanding, and it works in my case, that the secondaries on the double pumper don't come on until you depress the gas pedal which can be adjusted as well. I get great mileage with mine as long as I keep my foot out of it, which is difficult to do with the double pumpers. I personally liike the advantage of knowing that my secondaries will open manually and will let you know they opened everytime. Vacuum secondary carbs just don't that all the time.
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