I recently looked at the spring issue of one of the snowmo mags and they had results of a stock and mod shoot out. The big bore kits on the ZR900 did not seem to provide a lot of increase for the money. There were some numbers where the the stock outperformed the mod machine, even if it was one out 10 measurements. One engine was the D&D 1010 kit with twin pipes. FWIW
I was out racing this weekend and there was a guy with countryside 1010 and my friends 900 with twin d and d pipes, porting, clutch kit, reeds was just as fast at the 1010 I would save your money and stick with a ported 900
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