Need Help! May need lua Expert?

I just need the engine tones to emulate a set rpm range.. this one has rpms like so..
Idle rpm: 200rpm
Low hp rpm: 700rpm
High hp rpm: 2100rpm
And its not going to put out that rpm. Its just simulating it as sound. So just make it use the synthesizers provided for sound. And making a different switch is allowed if you wish to take the challenge of figuring out how i made this..