Help me pick my new carb

[foghorn67]

I have decided to give the Road Demon the boot. It runs way too rich when idling. And it is way oversized. Too bad, she looks pretty.

I have decided to get a Street Avenger. But which one? the 570cfm, or 670cfm. Holley recommends the 670cfm for over 300hp. But the old calculation everyone uses to figure out their cfm needs works close to 570cfm. Sometimes a little over when adding the 110% rule.
I know fords love something slightly bigger then what is supposed to go on there. But I really want to responsivness of a smaller carb without giving up high revving fun.
Any input?

 

['66427coupe]

a lot depends upon how you are going to use the car, (how many cubes, shift points and launch rpm's should be taken into account) you mention high revving which would make me say go with the 670. i used to run a fairly modded 289 with a 650 double pumper which was a decent combo. if the 670 has vacum secondaries it should be fine.

btw how big was your last carb?

 

[foghorn67]

[QUOTE='66427coupe]btw how big was your last carb?[/QUOTE]
It is a 725cfm. which is like way bigger in the Holley world. It is a silly size.

 

[rbohm]

go with holley's recomendation in this case. it is based not only on what airflow the engine needs, but what size injectors they are installing as well. also consider the fact that you are dealing with efi rather than a carb, and everything pretty much works on pressure instead of vacuum. since there is no vacuum signal needed to get fuel flowing, you dont need high airflow at low speeds, that a smaller carb would give, to get the fuel flowing to the engine. also since fuel in being sprayed in under high pressure, it is being atomized far better than it would be in a carb. you could even go with holley's four barrel efi throttle body that flows something like 700 cfm without the problems that a 700 cfm carb would cause.

 

[mustangdave]

rbohm,huh? I think he's talking about a street avenger carb., not an e.f.i. setup.