vern2point3 wrote: That said I've seen old Indy cars re-powered with various 4-cylinders and even supercharged Mazda rotaries that are putting out a range of 400 to 700 hp.
A 2 rotor can make that kind of power with no internal modifications other than work that is done with a die grinder (probably a good idea to use different from barrings, but that's not really an added expense).
One issue I can imagine when using a street car engine in a formula car is that their engines are typically stressed members. Star Mazda obviously gets around this.