500 AVS2 or 650 AVS2 ???

How does it affect performance?​

Vacuum is actually a measurement of the engine’s inefficiency. Higher vacuum indicates that the engine is working harder to breathe. This limits performance. However, it is necessary. Restricting the airflow and creating vacuum helps slow the engine down and limit rpm.

The vacuum created by the piston pulls air from outside, through the intake, into the cylinder. The throttle blades create restriction. This reduces the amount of air/fuel that goes into the cylinder. With less air/fuel, the engine cannot turn as fast.

As the throttle blades open, restriction and vacuum are reduced. This allows more air/fuel into the cylinder and rpm increases. With the throttle wide open, airflow is maximized and vacuum is at its least.

When you let off the throttle and the blades snap shut, rpm is still high. This creates a spike in vacuum. The restriction starves the cylinder of air/fuel. The result is falling rpm and vehicle deceleration.