I just put one one my cup racer. I love it! The motor is about 10mm longer than a standard brushless motor but still fits.
I change up the gearing to a the larger 67 spur and a smaller 27 pinion (65/30 stock). No heat issues what so ever, all the speed I could ever want plus some and long run times.
I'm also running the new Team Orion rounded hard case IBS 4000mah lipo (tight squeeze but it will fit with the hpi battery cage)
Fun car for sure.