I don't admit to modifying my motors, but I'm not saying I don't. If anything, I find more out at the track with extra plugs and gears than I would at home with a dyno.
Besides if you are moding your own motors you need to be really sure about what you can or should modify. plus the need for extra parts if you screw up. I can take a box stock mt 12 re and be one of the leaders all day without having to mess with the motor. fresh plugs good tune and clutch tweak and gears, I think that is all you need.