Moderator & USAF (Retired)
Join Date: Nov 1999
Location: Tucson AZ
EFi is the easiest way to "tune" a combination.
But, the difference in blow through versus suck through carbs. With the Blow through carb, and the vent tubes under pressure, you size the carb to the engine displacement and the boost is applied to the fuel volume as well as the engine, and the fuel curve is boost refrenced.
You have to pay attention when using a fuel pump so that the regulator is also boost refrenced and the fuel feed to the carb is able to overcome the blower pressure in the bowls on the needle and seat.
If you go through a suck-through system, you have to size the carb to the volume of air the blower will move. This requires a very large carb, but idle air speed is usually very low, as is the transition from idle to boost.... so the fuel curve is very difficult to tune. The carbs are usually pathetically fat at idle and part throttle, and work OK at WOT.
FOr blow through, you can use your 600cfm carb on a 302. For a suck through, your looking at 950 to 1250cfm..... to allow the carb to flow the air, and not exceed 1.5" of vacume beneath the throttle blades at WOT. If you have more than 1.5" of vacume below the throttle plates carb is too small, WAY TO SMALL>... and thecarb wont have large enough fuel passages to move the volume the engine is pulling.