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600 or 750 for a stock 390

 
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Old 08-23-2011, 07:45 PM
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600 or 750 for a stock 390

I didn't think i'd finally buy a 600cfm carb for my 390 till next year, but saw they were on sale at summit so i decided to go ahead and do it. Engine just has headers and the holley dominator intake. The carb i bought is a 1406 edelbrock. Everyone here seems to suggest the 600cfm for a 390, and 750 (what i had on it previously) was too much. Well after a short drive with the 600 on, it seems as if the truck has a little more off the line grunt, but everything else seems to be the same if not, not as good as the 750. It was only a short drive so i cant make any hardcore comparisons, but i felt that the 750 let the engine wind up a little faster....

Let me know what you guys think and have to say if anything.

I'll take it out for another spin in a few days to really mess around with it and see how it does again.
 
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Old 08-23-2011, 08:33 PM
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A 600 properly jetted should be fine for a stock 390. The 428 CJ came with a 735.
 
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Old 08-23-2011, 08:37 PM
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Originally Posted by 69cj View Post
A 600 properly jetted should be fine for a stock 390. The 428 CJ came with a 735.
By "properly jetted", do you know the actual jet sizes to use or to have someone else do that?

The carb seemed to work fine, just thought the 750 did a LITTLE better with taking off out of the equation.
 
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Old 08-23-2011, 11:49 PM
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Originally Posted by 69cj View Post
A 600 properly jetted should be fine for a stock 390. The 428 CJ came with a 735.
The standard 428 also used the 600 CFM carb. Any bigger carb is a waste of time and money because the engine will not turn enough RPM to need more. The 390GT also used a 600 CFM carb and it made max power at 4800 RPM.
 
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Old 08-24-2011, 02:16 PM
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well figured i'd put this out there if anyone feels like answering, both carbs did this. If i press the gas pedal to the floor from idle, it backfires through the carb some then keeps idling still. What is causing this? I thought maybe it was just too much carb with the 750, but even with the new 600 it does it to. timing?
 
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Old 09-03-2011, 11:42 PM
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pump adjustment. iirc, edelbrock has multiple settings.
 
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Old 09-03-2011, 11:46 PM
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for factory jet sizes, you can download the holley parts list from their website, shows parts, including jets, by holley list number. 22 pages in pdf.
 
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Old 09-04-2011, 05:15 PM
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i don't have a holley, though it was suggested to me by someone that i should have gotten a holley based carb if i wanted more performance out of it. Nothin I can do now though i can't return after it's already be in use. Works good now though.
 

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