what size of cfm carb do i need ?

[oldnelly87]

i got a 428ci small block chevy dart little m block, dart pro 1 heads 215cc 14:5:1 compression 4.000 stroke 4.125 bored and 6 inch rod , 645 lift roller cam straight acrossed. I don't know what size of cfm carb to put on it. its going in my outlaw super stock car weighs 3200 pounds 700 gears in rear and bert transmission I run it on a 1/4 mile dirt track runs on methonal. I have a 800 cfm c&s but I don't know if that's enough my chip is set at 7800rpms .

[perfconn]

428ci÷2=214ci
214cix7800rpm=1,669,200 ci per rpm
1,669,200÷1,728(ci per cubic ft)=965.97cfm

[rcstreet1]

how did you get the 1728 ci per cubic ft

[perfconn]

One cubic inch is 1"x1"x 1" so a cubic foot is 12ci x12ci x12ci or 1728 ci since carburetors are rated in cubic feet you must divide the ci per minute by 1728 to get cfm.

[perfconn]

If you size a carburetor for dirt track racing always err on the small size or acceleration will suffer.I just got through dynoing the 360ci engine up in the classifieds and the Willys dyno carburetor they started the engine with was a 1050 but it had poor acceleration so he bolted on a new Quick Fuel 950.The acceleration rate picked up and he tried to sell me that carburetor.I turned him down because I have dynoed and raced enough of these engines to know an 850 will race best.

[let-r-eat]

An 830CFM will be fine.

[perfconn]

Another thing to be wary of is carburetor ratings.A Holly950HP will not flow the same as a Quick Fuel 950.Most engine builders go by venturi size.