What does the CFM refer too specifically and how is it measured? I have tried to find some articles on this, but have had no luck at all getting a good explanation. Any carb experts out there?
Jay
Jay
Carburetor CFM
- Thread starter Garage Hound
- Start date
DOUG213XRJ said:
Okay, just so I understand, CFM refers to the amount of air volume (in cubic feet) that can pushed through the venturis in one minute? If that is right, then it basically comes down to the size of the holes in the base?
It's airflow in cubic feet per minute, as stated above. For all 4bbl carbs that is measured at 1.5" of vacuum under the carb, throttles wide open. 2bbl carbs are measured in the same manner but using 3" of vacuum underneath.
There's more to it than just the throttle bore diameter that affects airflow. Venturi size and design (including the booster venturis) can also have a significant effect on airflow capacity as well.
Back in the old days they used to rate carbs based on the diameter of the main venturi and the throttle bores. Hotrodders soon discovered this didn't tell the whole story and eventually those methods of measurement fell out of favor and out of general use. The carb's CFM flow rate became the new yardstick by which they got rated and advertised- and it's still that way today.
There's more to it than just the throttle bore diameter that affects airflow. Venturi size and design (including the booster venturis) can also have a significant effect on airflow capacity as well.
Back in the old days they used to rate carbs based on the diameter of the main venturi and the throttle bores. Hotrodders soon discovered this didn't tell the whole story and eventually those methods of measurement fell out of favor and out of general use. The carb's CFM flow rate became the new yardstick by which they got rated and advertised- and it's still that way today.
Damon said:
X2, but beware of published specs for aftermarket carbs. Some guys use vastly different vacuum levels to get their ratings, but don't say it in their ads...:roll:
Tommy
