Pop-up high compression. 9.5:1 CR. Piston weight 392gr. Piston pin weight 97gr. Head type: Dome. Dome -9cc. Compression height 1.375″. Bore 3.4980″. Stroke 4.250″ (4 1/4″). Rod length 7.440″. Cyl. length 5.550″. Comes with T6 heat treated 390 Hypereutectic cast pistons with 16% silicone levels which enables running a very tight clearance for longevity and hardly any piston noise. Note: Top compression ring will need additional clearance. See instructions.