- Fuel, Carbs & Intakes
- Carburetor Tuning Components
- Carburetor Power Valves & Accessories
- Holley Power Valves
What does a power valve do? The power valve allows the carburetor to function much leaner for part-throttle fuel economy but once the throttle is in a wide-open position#, vacuum in the manifold drops to almost zero and the power valve enriches the fuel mixture. When the engine is returned to basic part-throttle operation and vacuum rises#, the power valve closes up#, leaning out the mixture. The power valve is important because of its effect on everyday#, around-town drivability.
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The rule of thumb for power valve size selection is to divide your highest part throttle manifold vacuum reading by two and select the closest size smaller. Example: 8" Hg of manifold vacuum would use a 3.5" Hg power valve. Holley power valves include gaskets (thread size: 1/2-28).