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| | | | Joined: Nov 2000 Posts: 1,969 'Bolter | | 'Bolter Joined: Nov 2000 Posts: 1,969 | Does anyone know the carburetor cfm rating or capacity for a stock 216 (Rochester C)? Is that info published somewhere?
I have seen some online calculators where you input the displacement, max rpm and efficiency and it gives a result. Thanks.
Professional Novice
| | | | | Joined: Nov 2002 Posts: 2,766 Carburetion specialist | | Carburetion specialist Joined: Nov 2002 Posts: 2,766 | I have not seen published ratings on the Rochester B (there is NO Rochester C, and never has been).
The published rating on the M (superseded the B) with the 1 7/32 main venturi (this size used on the Chevrolet 216) was 160 CFM
1 barrel and 2 barrel carburetors are rated at 3.0 inches of mercury.
4 barrel carburetors (until greed in marketing took over) were rated at 1.5 inches of mercury.
The mathematical conversion factor is the square root of 2 (1.414).
Dividing 160 by 1.414 gives 113 CFM when converted to the scale most folks refer to.
Jon
Good carburetion is fuelish hot airThe most expensive carburetor is the wrong one you attempt to modify. If you truly believe "one size fits all," try walking a mile in your spouse's shoes!The Carburetor Shop | | | | | Joined: Feb 2004 Posts: 29,818 Kettle Custodian (pot stirrer) | | Kettle Custodian (pot stirrer) Joined: Feb 2004 Posts: 29,818 | To calculate the theoretical (not actual) CFM of an engine, divide the displacement by 2 - - - -(216/2=108). Multiply half the displacement by the RPM (108 X 3000=324,000) and divide by 1728 (cubic inches in a cubic foot). 324000/1728 = 187.5 CFM. That's assuming 100% volumetric efficiency, which is impossible. A more realistic CFM for a 216 at 3000 RPM would be about 85%- - - - - -159.4 CFM. The above formula works for ANY 4-stroke engine, regardless of cubic inch displacement or the number of cylinders. Even racing engines with major modifications to intake and exhaust systems have a hard time getting more than 90% volumetric efficiency.
Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
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There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
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| | | | | Joined: Jul 2014 Posts: 892 'Bolter | | 'Bolter Joined: Jul 2014 Posts: 892 | So my guess is the setup Patrick's used to sell for 270 GMC with 5 ea. Stromberg 97s was a bit of overkill. I knew a guy once who had a 53 Chev coupe with a 270 set up like that including headers and he made quit a bit of money betting guys with 283-powered 55 Chevs on a drag race. It set up an intimidating howl at full throttle.
1951 3800 1-ton"Earning its keep from the get-go"In the DITY Gallery1962 261 (w/cam, Fenton headers, 2 carbs, MSD ign.), SM420 & Brown-Lipe 6231A 3spd aux. trans, stock axles & brakes. Owned since 1971. | | | | | Joined: Nov 2000 Posts: 1,969 'Bolter | | 'Bolter Joined: Nov 2000 Posts: 1,969 | Thanks! I fat fingered a C instead of a B. Sorry!
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