Carb advise needed

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Jul 29, 2009 | 02:19 PM

929nitro

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Melting Slicks

Joined: Feb 2007

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From: West Kingston RI

Carb advise needed

I bought a Edelbrock carb at a swap meet, never been on a car. My mistake was I listened to the guy selling that told mee it was a 600 cfm. When I got home I checked the numbers to find that it was a 500, model 1404. I have a friend with a Edelbrock 750, model 1407, willing to swap for the 500. My concern is, would the 500 will be to small but the 750 be to large, cfm wise? I have a rebuilt 350 325 hp motor with edelbrock performer intake.

Any advise on which would be my best route or should I just lookm for a 600. Will eventually be doing a 383 just happen to have the 350 for another project I was going to do so I thought I would put it in the vette for now.

Last edited by 929nitro; Jul 29, 2009 at 02:21 PM.

Jul 30, 2009 | 07:34 AM

Ganey

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Joined: Apr 1999

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From: CORVETTE 77 385 C.I. TEXAS

You are right that the 600 would be a good choice for your setup.

CARBS Tests TQ/HP
Look at the area under the curve for Edelbrock 600 & 750. 600 is better for your setup.
http://www.corvettefaq.com/c3/carbcomparo.htm

You should try the 1404 esp. if you have an auto.

750 for 383.

Jul 30, 2009 | 08:47 AM

929nitro

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Melting Slicks

Joined: Feb 2007

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From: West Kingston RI

Thanks for the advice. I'm leaning towards doing the swap and just buying a 600 for this motor and keeping the 750 for the 383, since the 750 only has about 10k miles on it.

Jul 30, 2009 | 10:34 AM

Derrick Reynolds

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From: In limbo

St. Jude Donor '13-'15, '17 thru '22

The "common wisdom" is that a bigger cfm carb will give you more high end Hp, while a smaller cfm carb will give you more torque at a lower rpm. Ganey's data, although it does support the idea, surprised me by how small the differences were. He only got 1 Hp difference between the 600 and the 750 Edelbrocks.

Jul 30, 2009 | 11:24 AM

929nitro

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Melting Slicks

Joined: Feb 2007

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From: West Kingston RI

If I remember right I was told that a basic 350 engine draws in between 600 to 650 cfm. So anything above that is pretty much wasted. Which is why I was concerned about both carbs in my original post. Correct me if I am wrong. I can turn wrenches but not up on a lot of technical performance stuff as to what is best to use. Triing to learn.

Jul 30, 2009 | 02:05 PM

CCrane65

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From: Wichita KS

As I recall, the original Holley carburetor for my '65 327/350 was 585 CFM so 600 would be about right.

cc

Jul 30, 2009 | 02:09 PM

CCrane65

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From: Wichita KS

Quote:

Originally Posted by PKguitar

PK, I think everything is relative. If you up the CFM on any one piece of an engine's air intake system you must ensure that each component down the line matches that CFM rating. So, the intake may be the next bottleneck or the heads.

cc

Jul 30, 2009 | 02:28 PM

Derrick Reynolds

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From: In limbo

St. Jude Donor '13-'15, '17 thru '22

Quote:

Originally Posted by CCrane72

That makes sense.

I was also thinking down the lines of engine size and rpm too. If I have a 350 cubic inch engine turning at, say, 5000 rpm, I am filling each cylinder with air/gas mixture 2500 times per minute, which works out to 2500x350/1728=506 cubic feet per minute so I think that means a 500 cfm carb won't get me past 5000 rpm no matter what other components are on the system. Of course, this assumes a vacuum of 0 at WOT, which is probably an OK assumption for a weekend hobbyist like me, but probably wouldn't get me very far in the world of carburetor design. Using PV=nRT, the volume and pressure are geometrically related so 3 inches of Hg at WOT would give me about a 10% increase in the volume in the manifold, so I might get it done, but I would be cutting it real close.