wb is the man to talk to about TZR's.

There are several TZR forums knocking around, this one seems good, nice memorable url as well!

The big difference as far as I know between the 3xv SP and R is that the SP spec barrels are what you want if you want to make some decent power.
The R barrels themselves are restrictive.
SP barrels, a different CDI and some pipes will net you 60+bhp.
R barrels and anything you want will not.
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Please do not PM me technical questions, if you can't find it on the Forum start a thread