First off i must add I'm indoors. small track. Also I run an RsPro so I just added some boost and some timing and viola I'm pulling those Tekin 4.5's down the straight and jumping the same jumps. I just have a more controllable power band and a happy car. an 8.5 will have more toque than a 5.5 outa the box tho. gear it for some torque and when you add timing your adding rpm which changes the whole game. My racing buddy did the same swap but he used a Tekin 9.5 and that thing is just as fast. the rspro is the equalizer.