I notice when I really step on the gas (pedal to the floor) the engine almost sounds lower like it changes an octave. Its a good sound so I'm not complaining just wondering if is suppose to do that?

The only mod I have is an air intake.

Thanks

 

Your engine is under load. It's normal. Good rule of thumb is: If it sounds good, it's probably okay. If it sounds bad, it's probably not. Thanks for your contribution....