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Senior Charter Member
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314 Posts
Discussion Starter #1
Guys,
Ive got a 302 345HP crate motor (XB3M) and am looking for a mechanical secondary double pumper carb. I cant figure out if I need the 4777 (650cfm) or the 4776 (600cfm). The engine will spin up to 6500 rpm. Im leaning towards the 600.

As a side note, how much gph should I be looking for in a mechanical fuel pump?

Thanks, Kevin
 

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3,154 Posts
For what ever it's worth. On your same engine I bolted on a 4777C 650cfm mechanical secondary, manual choke. I spin it to 6500 on open track and it is absolutely smooth on the street.

It runs clean and consumes more fuel than the ill running Cobra EFI system but runs wide open in 4th gear at 6200. The EFI topped out at 5800 in 4th.

3.55 gears.
 

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Premium Member
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9,134 Posts
Hi Kevin,
Either a 600 or 650 will work but a vacuum secondary carb should also be a good option. Track cars respond well to a double pumper but street cars do better with vacuum secondaries for off idle driving. I sell mostly Carter mechanical pumps for your application.
Mike Forte
 

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I have almost the exact setup and I have the 4777 - 650 cfm. I know a local engine builder and he suggested this carb.
 
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