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What actually changed between Gen III and Gen IV LS blocks?
The main Gen III → Gen IV changes that matter for swaps (PSI Conversion, Speedway, GM tables):
- 58x crank reluctor (gray sensor) and a 4x cam sensor moved to the front cover (Gen III: 24x, black sensor, rear cam sensor).
- Drive-by-wire throttle on all Gen IV, and EV6/USCAR injectors.
- Options on many Gen IV engines: Active Fuel Management (e.g., LH6, LY5, LC9, LMG, L94, L99) and variable valve timing (e.g., LY6, L92, L20, L96).
- New engine families: 6.2 L (L92, LS3, L99, LSA, LS9) and rectangle-port heads on the 6.2s and on the LY6/L96 6.0s.
Mounts, bellhousing pattern and most external dimensions carry over.
Confidence: medium — sources disagree or are limited; check the sources below.
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Sources
- General Motors LS-based small-block engine — Engine table — Wikipedia
- What Every LS Swap Builder Needs to Know About the PCM and Harness — PSI Conversion
- The Complete LS Swap Wiring Harness Buyer's Guide — PSI Conversion