By: Don Terrill (c) from Racingsecrets.com
Comparing carburetors by their manufacturer's cfm ratings is the number one mistake racers make when picking a carburetor. In the old days it was easy -Holley was the only game in town. Today, with more competition has come more methods for rating carburetor air flow - It has become very hard to compare apples to apples.
I recommend that you don't even look at CFM numbers.
What needs to be decided and in what order:
1. Air Flow Path Dimensions - Venturi and Throttle Plate diameters
2. Type/Series - 4150, 4500 (Dominator), etc
3. Manufacturer - Holley, Barry Grant, etc
4. Linkage Style - Progressive, vacuum, 1:1, etc
5. Booster Style - Down Leg, Annular Discharge, etc
Number one on that list is by far the most important decision you will make.
Questions that need to be answered:
1. Engine Size - More cubic inches = more cfm (size)required.
2. RPM - More rpm = more cfm (size) required.
3. Application - Racing on limited tires and need to kill some lowend? Try a larger carburetor. Got'er hooked and need some more lowend? You got it, try a smaller carb.
Never, and I mean never: Loan or get rid of a good carburetor. They all have their own personality and some are just better than others.
My notes: I agree with the never get rid of any carburetor comment. I did once. I let go of a decent carburetor because it didn’t work for my current application. I now wish I had it back as it might work for my current setup. Sigh.
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