take a look at this:
http://www.groupk.com/restof800sj.htm
Group K "Most full-out racing SuperJet cylinders are fitted with larger cylinder sleeves that can accommodate 85.5mm pistons (781cc). The 781 setups works great, but they required engine complete teardown to bore the top-case, as well as the extra cost of sleeving. For our F800, we opted to bore the stock sleeves as far as was safe, thus avoiding the costs of sleeving and case boring. The maximum diameter limit of the stock sleeve is 84.5mm. Given this, we opted to bore to 84.0mm to allow us room for later over-boring (84.25 & 84.50). While the base sleeve (that sticks out of the bottom of the cylinder casting) gets very thin, it is still stable enough to endure the operation of a 7200-7300 rpm engine. One nice side effect of boring the stock sleeves to 84mm is improved cooling (a result of the shorter “steel” heat path from the piston to the aluminum casting)."