Black powder coated cylinders. No need to bore-out the cases. With 3.927" bore S&S feels this is the largest bore possible that can be safely used with stock bore crankcase spigots. Fits stock 4" stroke 88" Big Twin models and increases capacity to 97". 9.7:1 CR with stock 85cc cylinder heads; 10.3:1 CR with S&S 79cc heads. The forged pistons requires no flywheel re-balancing and valve pockets are enlarged to acommodate oversize valves and higher lift cams. Note: S&S does not recommend boring OEM cylinders to a bore this large because of possible failing of structural integrity. Just one piston oversize (917503) available for this kit.