hey all you gear heads out there. i'm biulding a 355 chevy and was wondering should i go with a 650 or a 750 double pumper?

it is a 350 bored 030 with .275 dome pistons, comp 292h .501 lift cam, cast heads ported,polished and milled. manley 194 pro flow intake valves and 150 exhaust valves. weiand stealth intake, pete jackson drive gear. i think thats all but i might stroke it next summer, and put pro 1 alum heads on it. so what do you think?

any info would be great. thanks

 

It depends on the rpm band of your engine. There is a formula for proper carburation for a street car. You multiply your max rpm by the displacement of your engine. Then take that number and divide it by 3456. Then take the number from that equation and multiply by 1.1 So for your car im gonna estimate that your going to bring it up to 5500rpm. Your displacement is 355 so....

5500x355=1952500
1952500/3456=564.959
565.959x1.1=622.5

So a 650 cfm would be the best carb for your car. Equation complements of the Auto Math Handbook.

 

With your cam and compression, 750 double pumper. That equation stated that I needed a 550 cfm carb, switching from a 600 edelbrock to a 650 demon when my motor was stock grabbed me a full second. If you wanted an accurate measure you would take into account cam size, compression ratio, displacement, bore stroke, cylinder head flow, intake runner port size, etc, not just max rpm that you will be shifting at.

 

thanks for the reply's I been getting pro and cons for both. but i think the 750 would be the best since i am stroking the motor to a 383 next summer. question is the only diff. between a 650 and a 750 the base plate? meaning if you get a 650 you can turn it into a 750 by changing the base plate. i heard this but i don't know much about holley carbs. thanks again for your help.

 

I ran a 355 with that same cam, flat top pistons ported 292 heads, weiand team G intake, 10" converter, and a 4.11 12 bolt posi in my 70 SS. Get the 750 cfm. Especially if you forsee a 383.

 

I agree, go 750....definitely if your gonna up-grade it more soon

 

At school we have done dyno pulls to experiment with this formula. Our best results came from the engines that had the carb determined by this equation. Even with a 383, id think a 750 would be too big for your engine.

 

I've seen people run at a track with similar set ups trying out different carbs. They all ran a littel quicker with the 750 over a 650. I'll take faster track times over a stronger dyno pull any day.

 

Yes, the only way to really tell is a few trial and error runs at the track, but for a starting point i think i would want to start with the set up that gave me higer numbers on the dyno.