Once the main venturi diameter has been selected then an optimum throttle bore diameter may be determined.įor most applications it is better to select a smaller main venturi diameter than what will provide maximum horsepower output. The chart shows the relationships of engine displacement, RPM at which peak horsepower is generated and the main venturi size associated for these two parameters. To simplify the selection of main venturi size a chart is provided which was developed from the classical formulas and then adjusted to fit known dyno data. The relationship between main venturi diameter and throttle bore diameter is a balanced relationship that is optimized when kept within the guidelines recommended by the classical formulas provided below. Do not be tempted to select larger carburetors in the attempt to develop more power without engine modifications to support the larger carburetor sizing. The real answer is that main venturis are sized to provide the air flow required by your engine and that the throttle bores are sized to compliment the main venturi size.

It is true that larger throttle bores combined with larger venturis are needed to produce higher power outputs but only when the engine is designed to need these larger diameters. When deciding upon an appropriate throttle bore diameter for your carburetors it is easy to err by over-sizing them in the belief that a larger bore size will deliver more power.

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