? for Bill and other engine gurus

[Zero Fast]

We are currently running a steel head 2bbl motor. Carb is a 4412 with a 1" spacer, massaged and flows 600 cfm. Typical Carolina engine rules. Dart ported 215's, Roller cam, etc.. We will be running a upcoming race where the only difference is that a 4 bbl can be used. My question is since my engine combo was built around the 2bbl.. Would I see a considerable difference in performance by dropping a 4bbl on the motor? There is not a carb. rule. So what size carb should be used for my current 2 bbl combo? Heavy track,3/8 to 4/10 track size.:-?

[perfconn]

Carburator size is directly dependant on engine size and rpm.The formula is cubic inches divided by 2 times the maximum rpm divided by 1728=cfm needed.This is assuming 100% efficiency.Yes it will run better with a 4 barrel.

[j61]

i keep coming up with zero? what am i doing wrong?
355divided by 13000(6500x2)=0.0273 divided by 1728=0.0000
thats all the decimal points my calc has.

[perfconn]

Doing it wrong.
355 divided by 2, equals 177.5 times rpm(I don't think your turning 13000) but say 8000rpm,that gives you 1,420,000 divided by 1728 equals 821.76 cfm
In your case 355 divided by 2, times 6500rpm equals 1,153,750,divided by 1728, gives you 667.68 cfm.
Keep in mind that your engine would only need this size at the end of the straight a way.A smaller carb will get you off the corners better but may lay down a little on topend.

[mbaker76]

(cubic inches X rpm) / 3456 = cfm

Same thing but it saves a step or two.

[j61]

so a 600 or 650 would be plenty? running on 1/3 mile dirt track.2600 lb limited type latemodel,291 gm heads,12.5 to 1
i am now running one of speedways modified 750 carbs.
runs great now but would i see an improvement changing to a smaller one?

[perfconn]

Might be a little quicker off the corners but not as strong on the topend but passing is usually done off the corners.I would suggest comparing lap times with a 650 and a 750.Everything else is just guessing.