[Pete]

Are there any differences in what's allowed to be done to the inline-4 liter bikes between the two organizations? Also, does anyone know specifically what can or can't be done to the motors, beyond the typical 'limited modifications are allowed' that you see everywhere?

[SuperDave]

While your answering Pete's question, maybe you can answer this. What was (guest commentator) Colin Edward's gripe about 'air restrictors' on the GSXR1000s versus the Ducatis during this past weekends race? He mentioned the air restriction a couple times throughout the race. If so, why are the iL4's restricted if the twins are pulling away in the straights?

[dB]

I didn't hear Colin's comments but I can take a pretty good guess at what he meant. Theoretically, an I4 can make more power than a twin of the same displacement by revving higher. WSB wanted 1000cc I4's in the game, since most manufacturers have pretty much given up on the 750s and they were being outrun anyway. So they mandated air restrictors for the 1000cc I4's to make them comparable to the twins. The size of the restrictor was probably determined by mathematical calculation, or possibly testing, but it's pretty clear that they went too far when the Ducs can easily pass them on a straight.