In recent years LS engine technology has revolutionized the GM performance aftermarket. Gen IV engines have set a new standard for factory horsepower and torque. To meet the growing demand of today?s high performance engine builders and racing enthusiasts engineers at RHSesigned an aluminum LS engine block for radical street and all-out racing applications.; Engineers at RHS have designed a high-performance aluminum engine block for GM LS applications to meet the needs of race and street performance engine builders alike. To go beyond the limitations of other existing LS blocks the new RHS LS Race Block is available in both standard deck and tall deck height configurations. Additionally this innovative aluminum block features a raised cam centerline and outboard priority main oiling to allow rod clearance for a 4.600” stroke and to minimize windage in the crankcase. And for quality control assurance RHS conducts a CT scan (similar to a medical CAT scan) on each block to ensure maximum casting precision and consistency. When you combine unmatched finishing quality with added clearance for increased stroke applications precision computer aided design and extra surface material to allow custom machining you get the new benchmark for LS horsepower torque and durability.; 54903U Specifications: Standard Deck Height (9.240); 4.120” Bore (Needs Final Finish Hone Before Assembly); 0.842” Lifter Bore; Raised cam centerline (.388”/9.86mm) to allow larger stroke; 2 extra links in the timing chain – Timing sets available from COMP; Machined for 55mm babbit (comes with bearings); Block Specifications: Designed from heavy-duty A357-T6 aluminum material; 4.125”-4.165” siamese cast bore walls w/ press-in spun cast iron liner; Available in standard (9.240”) & tall (9.750”) deck heights w/ beefy .750” deck thickness; Both standard deck (5.67”/5.87”- same as LS7) & tall deck (5.94”/6.38”) cylinder liner lengths available; “Long arm friendly” – Accommodations for up to 4.6” stroke w/ standard rod pin diameters (2.100”) & oversized 60mm camshaft; Main cap surface area maximized at mating surface & large fillets from cap to cross bolts for added strength; Designed for clearance – side oil galley moved outboard & engineered rod clearance come standard; Significantly increased windage passage area under bores & around caps over LS7/LSX engines; 6 head bolt design w/ full water jacket around the cylinders (based on LS7 design); Bay-to-bay breathing improved w/ increased side window area versus LSX & LS7; Extra-large windows in valley for access to inboard “6th” head bolt; Extra-long liners for standard (5.87”) & tall (6.38”) decks; Valvetrain Capabilities: Provisions for Gen III & Gen IV cam & knock sensors & valley covers; Cam tunnel will accommodate stock through oversized 60mm roller bearing cams (includes cast-in lock screw pads); .842” or .904” lifters standard with material available for oversized lifter access (accepts 1.060” bushing for keyed lifters); In the standard deck maximum pushrod angularity = Less than 2 degrees; Includes Ampco 45 cam thrust plate and aluminum rear cover; Lifter bosses designed to clear tie bar lifter