How To Calculate CFM:
Engine size (CID) x maximum RPM / 3456 = CFM
CFM @ 100% volumetric efficiency
(Example: 350 CID x 6000 RPM = 2,100,000 / 3456 = 608 CFM)
Approximately 608 CFM would be required for this engine. However, most Street engines are capable of achieving only about
80% VE; a modified street engine with ported heads, headers, intake and carburetor can achieve about 85% VE; a fully modified
race engine can achieve 95% or greater VE. The CFM number arrived at with this formula must be factored by this percentage.
Next, you need to decide whether a vacuum secondary or a mechanical secondary carburetor will work best for you.
As a rule of thumb, vacuum secondary carburetors work best on:
Relatively heavy vehicles
Street gearing
Automatic transmission
Engines built more for low-end torque
Conversely, mechanical secondary carburetors seem to work best on:
Relatively light vehicles
Strip gearing (4.11 or numerically higher)
Manual transmission
Engines built more for top-end horsepower
The type of choke would be the next decision to face. Most of the Holley universal performance carburetors come equipped
with either a manual or automatic electric choke. Manual chokes can be converted over to automatic electric choke operation
with the proper Holley kit, and vice versa.
Most automatic transmission kickdown linkage hookups will bolt directly to the carburetor throttle lever. Chrysler applications
will require the purchase of bracket, P/N 20-7, if it's not already included with the carburetor. Those running the GM TH-700R4
automatic overdrive transmission will require the purchase of bracket, P/N 20-95, for this purpose.
