Holley Carb

[Aussie67]

I am currently running a 600 cfm holley on a close to stock 302.

I know they work ok but what are the collective thoughts of changing down to 500, 2 barrel?

 

[ZFORCE]

Should be fine, I think Ford 4 barrel Mustangs originally came with a 480 cfm carb?

 

[Aussie67]

Thanks mate. I don't think I have ever seen a 480 over here. Are they a common item?

 

[msell66]

First off, why the need to change? Is it a dog with a 600? If really interested to try one, do it on a dyno so you know what the difference ends up being.

 

[Aussie67]

Not really a dog, just seems a little to much carb for a close to stock engine.

 

[Horseplay]

Going from a 600 4 barrel to a 500 2 barrel what are you hoping to see? You'll get better daily driver economy out of the 4 barrel and provided it is jetted and set up right you'll likely see more seat of the pants fun with it too. I fail to see any benefit changing to a slightly lower CFM 2 barrel.

 

[Midlife]

Going from a 600 4 barrel to a 500 2 barrel what are you hoping to see? You'll get better daily driver economy out of the 4 barrel and provided it is jetted and set up right you'll likely see more seat of the pants fun with it too. I fail to see any benefit changing to a slightly lower CFM 2 barrel.

I absolutely agree. The primary 2 barrels of the 4 barrel carb is more fuel efficient than the 2 barrel carb. If you think it is too much, why not go to the 480 cfm version (Autolite 4100) that was used in all A code Mustangs and is an excellent carb. The Summit version that is quite popular is based on the 4100 design.

 

[Aussie67]

OK, so I'll keep the 600 and put a recon kit through it. Its running but dies/ struggles on acceleration. Wanted to check the general thinking before going kit or new.

 

[Horseplay]

What you're describing is likely carb related and a good cleaning alone could fix it but doing a standard rebuild wouldn't hurt either. Be sure to check your incoming fuel line and filter as well. It could simply be a low or inconsistent fuel pressure issue too. If you don't have a fuel pressure gauge in place by the carb, now would be a great time to add one.

 

[swpruett]

Maybe another way to consider this is that 4bbl Holley carbs are rated at 1.5"Hg test pressure and 2bbl Holley carbs are rated at 3.0"Hg test pressure. So on equal terms, going from a 600cfm Holley 4bbl to a 500CFM Holley 2bbl would be the equivalent of swapping to a 354CFM 4bbl. That said, if that is what you are compelled to do, then a 390CFM Holley 4bbl would be preferable to the 500CFM 2 bbl and wouldn't require a total intake manifold tear-up in the process and make for a much easier pill to swallow when regret sets in and you go back. *wink*.