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.

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.

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.

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?

pump adjustment. iirc, edelbrock has multiple settings.

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.

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.