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.