Andy,
I heard the Banshee motors heavily tweaked in the 500cc bigbore versions are about 70hp (all peaky), so the NSR has similar potential with better midrange, longevity and durability.
Alex,
first of all, where are you at? I am in WA State and have an MC28 parts manual. Most all the '28 stuff is interchangeable with the '21 stuff if you know what you are doing. I can help with that. Also, about your tranny: under heavy modding/high horsepower, the NSR has been known to have weak 2nd gear. Of course, this is coming from the guys at HARC PRO, who know these bikes at their extreme racing limits that most street riders never see. It would be a real good idea for drag racing to have the gears back-cut. And running the wet clutch, you may notice that it will only hold well to about 60-65hp before she slips. May not be noticeable if running in the sand, though.
Stroking the NSR is not an option. Noone has come up with a rod source as the NSR rod big ends are very big for a 125cc cylinder.
You may be better off parting the RS engine out and buying the Tyga 300 kit. The RS stuff is getting really rare and may go for really good prices.
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Paul Herr
'88 FZR4/GSXR/YZF Frankenbike
MY BIKE PICS