Eaton M90

The M90 is a 90 cubic inch supercharger (1.47 liters) in displacement. On the 3800 it was fitted with a 3.8“ diameter pulley and produced about 8 psi of boost from the factory.
Series 2 L67 engines were equipped with a generation 3 Eaton M90 supercharger and Series 3 L32 engines were equipped with the generation 5 (Gen V) M90. Both are quite similar, however the generation 5 M90 is slightly more efficient at making power. From the factory the generation 5 was able to produce 20 more horsepower according to GM.

The pulley on the M90 can be pressed off with a puller tool and replaced with a smaller pulley. There are also modular pulley hubs and pulleys that are available from the main vendors for the 3800.

Generally when swapping to a smaller pulley more supporting mods will be necessary to minimize the amount of heat being generated by the supercharger. Typically most recommendations are to install performance modifications to the engine to help it flow more air more easily to minimize the amount of pressure the supercharger has to make.

Another option is to install an intercooler below the supercherger to reduce the amount of heat it creates. This allows you to run a smaller pulley on the supercharger and can also help decrease heatsoak.

Without an intercooler the M90 will produce enough heat to induce a noticeable loss of power when making runs in quick succession. The intercooler will go a long way to make the power output of an M90 engine more consistent.

Switching to E85 will make a huge difference in heatsoak as well.

Most M90 powered cars will generally max out around 400 wheel horsepower with an aftermarket camshaft, headers, and an intercooler.

If you want to make more power than this then you may want to consider a larger supercharger or switching to a turbocharger.