Why is there no sound at high RPM after modifying the exhaust?

[DanielaRose]

Due to the presence of sound-absorbing cotton, there is no sound at high RPM. Here is more relevant information: 1. Only modifying exhaust backpressure: Simply modifying the exhaust backpressure and changing it to a straight pipe can increase the upper limit of the engine's net power output at high RPM. However, the improvement effect is not significant, generally ranging from 5% to 10%, which means recovering the power lost due to the original exhaust backpressure, and it only takes effect at high RPM. 2. Modifying backpressure combined with ECU tuning: This stage marks the entry into the threshold of modification. ECU tuning can increase net power output, and when combined with low backpressure, it can further expand the range of net power output, allowing the vehicle's performance to be further enhanced.