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LS heritage

The General Motors engine family commonly called the LS series debuted in the then-new1997 model year C5 Corvette as the all aluminum LS1 V8. General Motors called it the Gen III small-block V8 and a year later (the 1998 model year), the LS1 replaced the LT1 small-block in Camaros and Firebirds, which was followed by the iron-block version of the Gen III V8 appearing in the full size trucks and SUVs. The LS1 displaced 5.7 liters, similar to the previous-generation small-block, but the cubic-inch measurement differed slightly: 346 for the LS1 vs. the traditional 350 cubes.

In 1999, the Gen III platform spawned the higher-performance LS6 that was standard in the Corvette Z06. In 2005, the Gen IV branch of the LS family was born, differing from the Gen III with cast-in provisions for fuel-saving cylinder deactivation, larger displacements and revised camshaft sensing. The performance versions of the Gen IV include the LS2, LS3, LS9 supercharged, LSA supercharged and the LS7.

GM has continued to refer its modern V-8 engine family as Gen III and Gen IV, but to the enthusiasts who quickly grasped the tremendous performance potential of the engines, every engine based on the platform has been nicknamed "LSX." The range of production engines from the LS platform is wide. On the truck side, iron-block engines have included 4.8L and 5.3L versions, as well as all-aluminum 6.0L and 6.2L premium engines. Car engines include 5.3L, 5.7L, 6.0L, 6.2L and 7.0L displacements - including some configured for front-wheel-drive.

Gen III vs. Gen IV

Despite some significant differences between Gen III and Gen IV cylinder blocks, all LS engines share common traits that include:

* 4.40-inch bore centers (like the original small-block)

* Six-bolt, cross-bolted main bearing caps

* Center main thrust bearing

* 9.24-inch deck height

* Four-bolt-per-cylinder head bolt pattern

* 0.842-inch lifter bores

* Distributorless, coil-near-plug ignition system

The most distinguishing differences between Gen III and Gen IV cylinder blocks are larger bores (on some engines), different camshaft position sensor locations - indicated by a move to the front timing cover area on Gen IV blocks vs the top-rear position on Gen III blocks - and, on most Gen IV blocks, cast-in provisions for GM's Active Fuel Management cylinder deactivation system in the lifter valley.

There is great interchangeability between all LS engines, including between Gen III and Gen IV versions. Cylinder heads, crankshafts, intake manifolds and more can be mixed and matched - but the devil is in the details. Not every head matches every intake manifold and not every crankshaft works with every engine combination. Will Handzel's "How to Build High-Performance Chevy LS1/LS6 V-8s" - P/N 88958786 - is a great reference source that outlines the more specific differences and interchangeability among Gen III-based engines.