Pat
Supporter
What a difference a carb makes! It was time to put a rebuild on my CAV’s carb. While shopping for a suitable rebuild kit, I came across a formula for determining the appropriate carb for your car. In looking at it, seems that my carb was too big. Interesting in that my smallblock H.O. Ford came from the builder with a 750CFM Edelbrock and while the low end was acceptable, at 3,000 RPM the thing absolutely screams and 5-6,000RPM are an eye watering experience.
So I found a used Edelbrock 650CFM on EBAY, rebuilt it and put it on the car. The difference is amazing. The car’s street manners are so much better and the midrange is greatly improved with only a marginal loss on top end. So now it’s on the car and I only plan to use the 750 for track days.
Here’s the formula:
Multiply your cubic-inch displacement by the maximum rpm limit and then divide by 3,456 to represent the volumetric efficiency. The result is the amount of cfm the engine requires at the maximum rpm limit.
Example:
347 ci x 6,000 rpm = 2,082,000
2,082,000 / 3,456 = 602.4cfm
A 600-cfm carb would would be sufficient.
So I found a used Edelbrock 650CFM on EBAY, rebuilt it and put it on the car. The difference is amazing. The car’s street manners are so much better and the midrange is greatly improved with only a marginal loss on top end. So now it’s on the car and I only plan to use the 750 for track days.
Here’s the formula:
Multiply your cubic-inch displacement by the maximum rpm limit and then divide by 3,456 to represent the volumetric efficiency. The result is the amount of cfm the engine requires at the maximum rpm limit.
Example:
347 ci x 6,000 rpm = 2,082,000
2,082,000 / 3,456 = 602.4cfm
A 600-cfm carb would would be sufficient.
ffice
