Some hot rodders are reluctant to embrace the indisputable virtues of technology. Let's call them traditionalists. Others would rather push a Ford than drive a Chevy. Let's call them victims of brand loyalty. Then there are those who are more impressed by the number of valves an engine has, and the rpm it turns, than the tally it posts in the hp column. Now they're just out of their mind. In just a little over a decade, GM's LS engine platform has converted hoards of traditionalists and even Ford loyalists alike. These days, Gen III and IV small-blocks are popping up in everything from Chevelles to Mustangs, to BMWs, to Mazdas, to Jaguars, to Hondas, to Datsuns, and even Porsches. Staggering power, low mass, compact external dimensions, and excellent fuel mileage have made the Gen III/IV small-block the new King of engine swaps. Perhaps the most significant factor is the sheer number of LS motors now piling up in boneyards-which translates to cheap cores-and the constant influx of affordable aftermarket parts. Some of the cheapest and most potent hardware of all comes straight from the factory, as GM has continually updated the platform since its inception. There are now more than two dozen Gen III and IV variants in existence, so we've set up this guide to explain the differences between them to help you decide which is most appealing for your project car.
Much like the Gen I and II small-blocks, almost all the hardware amongst the different LS variants are interchangeable. In fact, except for the smallest (4.8L) and largest (7.0L) motors in the LS lineup, all share the same 3.622-inch stroke. In most instances, the cylinder heads, camshafts, crankshafts, and intake manifolds can all be mixed between different LS motors. Furthermore, while Gen III and IV truck motors are usually labeled "Vortec," they share the exact same architecture and many of the same parts as their "LS" designated counterparts. Vortecs were once distinguishable by their iron blocks and heads, but that's no longer the case since many trucks now come equipped with all-aluminum engines. Interestingly, only minor differences distinguish Gen III from Gen IV small-blocks. Gen IVs feature provisions for variable valve timing, active cylinder deactivation, and a revised camshaft position sensor location. Otherwise, both generations of motors are very similar.
The engines outlined in this guide represent every Gen III and IV small-block ever installed by GM in a production car or truck. Whenever possible, or relevant, we've included cam specs. At the current rate of LS engine development, it's quite possible that we'll need to add an appendix to this story in a couple of years. Happy swapping!
What We Did
Compile descriptions and vital stats of every production Gen III/IV small-block in existence
LS motors are cheaper, more plentiful, and more powerful than ever