LS engines are the most popular engines to build, swap, and hot-rod because of their availability, affordability, and compact size. (They fit pretty much anywhere that a Gen. I or Gen. II small block Chevy engine will.)

LS engines make up General Motors’ Gen. III and Gen. IV small block Chevy engines, and there are some differences between the two generations and telltale signs to tell them apart.

Things like the front timing cover, knock sensor location, cylinder head style (cathedral ports), AFM (Active Fuel Management), and other components are key clues to which engine family you’re looking at.

In today’s video, our friend and resident LS expert Brian Nutter at Summit Racing covers some of the main visual differences between the two engine generations.

Once you’ve determined whether you’ve found an LS Gen. III or LS Gen. IV engine, you can narrow the engine down by RPO code.

We have a highly comprehensive LS engine tech article library (much of it authored by Brian from the video), including the engine specs, and engine code-specific upgrade advice for every engine in the LS family. You can find all of those in one place: The Definitive Guide to LS Engine Specs and LS Engine Upgrades.