If you apply the Rocketbunny kit onto the NSX the car spits flames left and right but with the RB Kit the exhausts are in the middle.
The nissan s15 is the same way when you apply a back bumper, the flames come out the middle instead of the muffler.
I read somewhere else that changing the camera view a few times can fix this. If not, rebooting the game should surely fix it.