[vern650]

this is what i read-

The Vortec 8100 (RPO L18) is a V8 truck engine. It is a redesigned Chevrolet Big-Block engine and was introduced with the 2001 full-size pickup trucks. It is an all-iron engine (block and heads) with two valves per cylinder. It retains the same bore centers as the old 7.4 L big-blocks, but stroke was upped by 9.4 mm (0.4 in) to reach 8.1L (496cuin) for a total of 107.95 mm (4.3 in) bore and 111 mm (4.4 in) stroke. Power output ranges from 325 hp (242 kW) to 550 hp (410 kW) and torque from 455 lb·ft (617 N·m) to 690 lb·ft (936 N·m). Vortec 8100s were built in Tonawanda, New York. The Vortec 8100 is the engine used in the largest Uhaul, their 26-foot (7.9 m) truck. GM stopped installing big block V-8's in the Silverado HD trucks, when the GMT-800 series was discontinued in 2007. 8100 marine engines range from 400 to 600 hp (447 kW) and come with a stand-alone Engine Control Module (ECM). The last L18 was manufactured in December 2009.

Important differences between the Vortec 8100 and older big blocks include a changed firing order (1-8-7-2-6-5-4-3), a new 18-bolt head bolt pattern, different symmetrical intake ports, different oil pan rails and the use of metric threads throughout the engine. The fuel-injection system for the Vortec 8100 is nearly identical to that used on Gen III engines, right down to the fuel and spark tables in the ECU.[25]