Volume III, Issue 12, Page 30

This GM engine family, commonly called the LS series, debuted in the 1997 C5 Corvette as the all aluminum LS1 V8, AKA the Gen-III small-block V8. The following 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.

In 1999, the Gen-III platform spawned the high-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.

Though GM has continued to refer its modern V-8 engine family as Gen-III and Gen-IV, but enthusiasts 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)

  • Though some LS, according to use, are built stronger than others, they all share the stabilization of a deep-skirt cylinder block, 4-bolt main bearing caps, and 2 horizontal bolts.

    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

Hands down the best manual of its type, GM engineer Will Handzel’s LS1/LS6 compilation is a must for the home-builder and shop builder alike. 

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 versus 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 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.


LS1 5.7L (346ci) engines were produced between the 1997 and 2004 model years in the United States (Corvette, Camaro, Firebird and GTO) and stretched into 2005 in other markets (primarily Australia). The LS6 was introduced in 2001 in the Corvette Z06 and was manufactured through 2005, where it also was found in the first generation of the Cadillac CTS-V. The LS1 and LS6 share a 5.7L displacement, but the LS6 production engine uses a unique block casting with enhanced strength, greater bay-to-bay breathing capability and other minor differences. The cylinder heads, intake manifolds and camshaft also are unique to the LS6.