is this right? (math involved)

[magnethead]

I have a 454 CID motor.

It is a 4 stroke, so it takes 2 rotations to make a power stroke.

therefore, it moves 454 cubic inches of air per 2 revolutions, correct?

454 cubic inches is 0.26 cubic feet.

My tach indicates 2800 RPM or so going 60 MPH.

That's 1400 power strokes per minute, correct?

therefore, wouldn't cubic feet times the amount of times that much air is moved per minute give us CFM?

1400 times 0.26 = 364 CFM.

Does that not mean a 375 CFM carburetor would be about right for my motor? (this is all hypothetical, i'd imagine there's losses in there somewhere?)

then why do I have a 650 CFM carburetor from the factory? Did i make a bad calculation or assumption?

[trkklr77]

if all you want is for it to run with absolutely no load on the motor, yes.



there is an old hot rodders formula [i dont know it myself] that will tell you "xxx" cfm carb will take "xxx" cid motor to "xxx" rpm. it is used to figure what cfm carb you will need, it say that to get a 454 to 5k it will only take a 623 cfm carb, in theoy it will but it wouldnt do it with much athourity.

[SanitysBane]

Well remember that your motor is a 4 stroke, intake, compression, power and exhaust. Acording to the back of my AFR book is gives this formula for cab size; Carb CFM required = (CID X Maximum RPM)/3456. So for a 454 times max RPM of 5000, is 2270000/3456 would equal 656.828 CFM. With your hypothetical MAX RPM of 3000(rounded) would be 454 X 3000 = 1362000/3456 = 394.097. So if all you want to do is run your engine at 3000RPM, at no load than go for it, and yes their are losses to take into acount as well. Also remember the more horsepower that you make, the more air you are going to need and vice versa. If you are thinking about putting on a smaller carb for better fuel millage than get a motorcycle.

[magnethead]

Originally Posted by SanitysBane

Well remember that your motor is a 4 stroke, intake, compression, power and exhaust. Acording to the back of my AFR book is gives this formula for cab size; Carb CFM required = (CID X Maximum RPM)/3456. So for a 454 times max RPM of 5000, is 2270000/3456 would equal 656.828 CFM. With your hypothetical MAX RPM of 3000(rounded) would be 454 X 3000 = 1362000/3456 = 394.097. So if all you want to do is run your engine at 3000RPM, at no load than go for it, and yes their are losses to take into acount as well. Also remember the more horsepower that you make, the more air you are going to need and vice versa. If you are thinking about putting on a smaller carb for better fuel millage than get a motorcycle.

lol i was just trying to figure out why i had a 650 (or a 750, haven't looked up the carb to see which version I have).

FYI, the redline for a stock 454 is 4200 RPM or some number around there