This one is pretty simple and should be easy to implement. The 4 rotor is underpowered and is missing the ability to add turbochargers. Antilag would also make it sound even more amazing.
Id imagine a race turbo upgrade could put it at around 1200hp and make it a suitable engine for higher class racing, at the moment its stuck as being not good enough for s1 and unable to reach A.
Please add this option to this beautiful engine PGG!