The C5 carburetor size calculator will help you understand the "RANGE" of cfm needed from high rpm to low. Regardless of the reason, as rpm drops, so does the required cfm. Determining the low and high rpm range during a pull will help you choose the correct size carb, with particular focus on where your "peak torque" will be for the best match.
A carburetor that is too large for the application will not operate correctly at low rpm and with low manifold vacuum. It can cause erratic A/F readings and cause lean running during heavy loads.
A carburetor that is too small will work great at low rpm but limits horsepower at high rpm and may begin to exhibit A/F bounce as the signal starts to fail.
We hope this provides you with a better understanding of how a change in engine size or target rpm affects the intake/exhaust math.
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