[Shotimes] (OT) Rotating mass and dyno tests

[Ron Porter]

Last night, Speed had an episode of Sports Car Revolution. One of the
segments dealt with the Mugen Acura that they are modifying. I had not seen
the earlier episodes, but in this one, the installed bigger brakes and an
exhaust system.
They were expecting about 5 whp for the exhaust, and when they ran it, the
car lost 7 whp. They reinstalled the stock exhaust, and then lost 12 whp!

What they determined is that the larger brakes caused the net 7 whp loss, as
these were the only changes. I didn't catch which brakes they installed, but
they had bigger rotors, and although each corner's total brake weight
(unsprung) was reduced by 1.9#s (probably most of it in the caliper weight,
I would guess.....they didn't break out rotor/caliper weight differences),
the bigger diameter rotors added more rotating weight by moving the mass
farther from the center of the hub.

When modifying your car with either bigger brakes or heavier tires, it
"will" have an effect and a heavier wheel/tire comb will have a greater
detrimental effect on whp than larger rotors.