Blow-Through Carburetor Selection
When selecting a carburetor for your ProCharged blow-through application, as with naturally aspirated engines, less is generally more. A carburetor can be sized according to your engine’s airflow and resultant power output. Even though a larger than recommended carburetor may offer some increase in peak power, it will likely cause the engine to be less responsive at low RPM and result in drivability unacceptable for cars that will be street driven.
Preparing a carburetor for use in a blow-through application typically involves few, if any modifications. Among those needing no modification are Holley’s HP series carburetors which are designed with no choke assembly and generally equipped with Nitrophyl floats from the factory.
But what if you have Holley’s most popular carb … the Double Pumper? For standard Double Pumper carburetors, the choke assembly should be removed to provide optimal airflow and performance when used with a carburetor bonnet. Additionally, the brass floats (which will collapse under boost) must be replaced with Nitrophyl floats (available from ATI, or Holley). With only the modifications listed above, Holley Double Pumpers (when properly jetted) will typically flow enough fuel to support 1 hp per rated cfm of airflow. Single carburetor applications exceeding 1 hp per rated cfm may require additional modifications such as resizing main wells and power valve restrictions, changing boosters and emulsion circuit recalibration.