High Performance XS 650 Wiseco Replacement Pistons

and Engine Displacement Formula

Stock Bore 75 mm piston on the left, Wiseco forged 81 mm on the right.

A pair increases displacement to 763 cc's.

Stock compression ratio is 8.7 to one (right side above), replacement is Wiseco forged street or track performance ratio of 10.25 to 1. New cylinder sleeves need to be installed.

Replacement cylinder sleeves above.

Piston domes are nearly identical, increase in compression ratio comes from the increased swept volume of the larger bore. Stock piston fits inside the 81 mm piston kit (above)!

Wiseco has 80 mm piston kits = 744 cc's

and 81 mm piston kits (shown above) = 763 cc's

Stock bore is 75 mm & stock stroke is 74 mm = 654 cc's

Engine Displacement Formula:

bore X bore X stroke X 2 X .786

where the number 2 in the above line is the number of cylinders

Old round skirt XS650 Wiseco piston set above with "Spiral Lock" wrist pin retaining clips. The "Spiral Lock" retaining clips do not work!! You must use wrist pin buttons with this style piston. Due to high piston speeds and direction change one end of the spiral locks almost ALWAYS comes out !!! Don't think you put one of those clips in wrong, they are absolute trash. Bob B.

Venolia 12 to 1 ("C" clip style)

New style Wiseco with "C" clip wristpin retainers. (above and below)

We have never had any problem with any "C" clip wire style wrist pins retainers.