HALP Shifting engine sound

Its for my wheelie monster,
I need 4 gears.
No reverse (unless you wanna make a extra synth system for the backup noise)
No changing the pitch or tone of the current synths, you can take the values of them to add extra synths, but no taking them for personal use unless you're ZardOz, that guy, and anyone else who has helped with something (both giving tips, and actually helping with some of my levels)
LUA MUST BE TWEAKABLE AND HAVE SOME FORM OF EXPLAINATION ON HOW IT WORKS(dont write a friggin english paper though)
I highly recommend you build on a seperate bread board, and use as little wifi items as possible.