This is the same block that was used in the LeMans 24 hour endurance racing C5R Corvettes and is intended for maxium effort competition engines. This block has the same production external dimensions and bosses, with the primary difference of this block to the Gen 3 production blocks is siamesed water jacket, which allows engine builders to build engines with larger bore sizes. The delivered, post hone, bore size is 4.00" and the maximum finished bore size recommended with this block is 4.160". Cylinder deck height is 9.240". This block uses a dry, pressed in liner similar to other GM Racing aluminum small blocks. Steel billet bearing caps are fitted to the block. This block features wet sump style oiling and is made from high strength A356 aluminum that utilizes a modified T7 heat treat. Production Gen 3 style cylinder heads may be used on this block, however for maximum performance, P/N 12480005 Gen 3 racing cylinder heads should be used.