The LS swap has become the go-to engine upgrade for full-size Chevy and GMC trucks — and for good reason. Whether you’re building a Squarebody C10, an OBS GMT400, or a GMT800 Silverado, the Gen III/IV LS family drops in with proven reliability, massive aftermarket support, and power figures that embarrass anything the factory ever bolted in. It’s not just popular — it’s practically become the default answer when a tired TBI 350 or worn-out Vortec hits high miles.
For the full written breakdown — engine choices, mount kits, oil pan clearances, wiring harness options, and tuning — check out The Complete LS Swap Guide for Chevy & GMC Trucks on FullSizeChevy.com. That article covers the whole process from junkyard pull to first start. Here’s a summary of the main decision points to get the conversation going:
Engine Choice
The LM7 (5.3L, iron block) is the budget king — cheap to find, easy to tune, and makes 270–300 hp stock. The LQ4/LQ9 (6.0L) steps things up without much cost penalty. Want aluminum? The L92/L96 gives you rectangular port heads on a budget. LS2, LS3, and L76 are higher-dollar options that make sense if you’re chasing 400+ hp without forced induction.
Motor Mounts
Platform-specific mount kits are non-negotiable. ICT Billet and Dirty Dingo are the two most popular brands and both make kits for Squarebody, OBS, and GMT800 applications. Don’t try to adapt factory mounts — you’ll fight header clearance and steering shaft issues the whole time.
Oil Pan
The stock car/truck LS oil pan will likely hit your crossmember or steering. The Holley 302-2 (swap pan) is the most common solution. Some OBS and GMT800 frames can run a stock truck pan with the right crossmember notch, but confirm fitment before you bolt the engine in.
Wiring / PCM
You’ve got two paths: (1) keep the factory ECM with a modified harness, or (2) go standalone with a Speartech, PSI, or Painless harness. The standalone route is cleaner for dedicated swap builds. If you’re swapping into a truck that uses the same LS-generation electronics (like a GMT800 upgrading from a worn LM7), a stock harness swap is often the simplest move.
Transmission
Most LS swaps run a 4L60E or 4L80E. The 4L60E handles up to about 400 rwhp reliably. Anything above that, or if you’re towing hard, go 4L80E. The adapter crossmember and driveshaft length will need to be addressed either way.
Alright — let’s hear it: what platform are you swapping into and what engine did you choose? Drop your build details below — engine, trans, any surprises along the way.