There are two important factors to consider when searching for a set of cylinder heads for an LS engine. The first consideration is the type of intake manifold port; the second is piston bore size of the engine block.
First, let’s talk about the types of GM LS intake port designs. General Motors has three different designs for the LS engine: cathedral port, rectangular port, and raised rectangle port. The cathedral port is the most popular and can be found on the LS1, LS2, LS6, the Vortec 4.8L, 5.3L, LQ4, and LQ9 engines. The raised rectangle intake port design can be found on the LS7 and LSX engines. Finally, the rectangular intake port design is on the LS3, L92, L99, L76, and LY6 engines.
More information on LS Intake Manifolds can be found here.
Now on to the second part–the piston bore size of the engine block. GM made quite a wide range of engine blocks with various piston bore sizes to account for different displacement size engines. The 3.89-inch bore LS1 and LS6 engines can only use cylinder heads designed for a LS1, LS6, or LS2 engine. The reason is the valves will come in contact with the sides of the piston walls if a cylinder head for a larger bore engine is used. The LS2 and LQ9 engine block has a 4.00-inch bore and will accept LS1, LS6, LS2, and LQ9 cylinder heads, as well as cylinder heads from the L92, LS9, and LS3. The 6.2L engines have a 4.065-inch bore size and can accept all of the smaller production style cylinder heads. Finally, if you have gotten your hands on a LS7 or have decided to work with a LSX engine block, those have an even larger bore size and you should work with your engine builder to find the right set of heads for your project.
The chart below provides a quick outline of LS engine/cylinder head compatibility.
There are a few engine blocks that we haven’t mentioned, most notably the LS 5.7L, 5.3L and 4.8L iron block Vortec engines. The 4.8L and 5.3L engine blocks have a 3.78-inch bore and require cylinder heads designed for the smaller bore size. Thankfully, companies like Trick Flow Specialties have stepped up and produced heads for these engines. Trick Flow, for example, has designed its GenX Cylinder Heads for the GM LS 4.8L, 5.3L, and 5.7L Vortec engines.