Non-production cylinder blocks
C5R: Developed for the factory-backed Corvette racing program, the C5R cylinder block has been manufactured in comparatively small quantities since 2000. They are manufactured with a unique aluminum alloy for greater strength and undergo a variety of specialized machining and inspection processes, including “hipping” to increase strength and X-raying that ensures against unacceptable porosity. A Siamese bore design with 4.117-inch finished bores enables 7.0L (427-cu-in) displacements. The C5R uses billet steel main caps with premium, 4340 fasteners. Racing-quality head studs are also included. All LS series heads will work with the C5R block, but maximum performance depends on maximum airflow.
LSX Bowtie Block (standard and tall-deck): Introduced in 2007, the LSX Bowtie Block is a durable and affordable cast iron casting that was designed to support extreme high-performance combinations, including provisions for six-bolts-per-cylinder head fastening. It has a Siamese bore design with 3.99-inch bores that must be finished to 4.00 inches – with a 4.25-inch recommended maximum bore. Maximum stroke can reach 4.25 inches, but rotating assembly interference on the cylinder must be taken into account for strokes greater than 4.125 inches; heavy metal is required for crankshaft balancing of larger-stroke combinations. Standard versions feature decks 0.020-inch taller than LS production blocks, with the tall-deck version manufactured with a 9.70-inch semi-finished deck height. The oiling system is a true priority-main system and all LS small-block heads work with the engine. Higher-airflow heads, such as LS7 and C5R, are recommended.