These Steeda Supercharger Pulleys are made from Steel not aluminum and have holes drilled around the center of the pulley to lower the rotational weight. This is the highest quality pulley available for the Cobra.
3.10" pulley 1-2psi over stock, requires performance tune.
Testing has shown 25+ horsepower.
2.81" pulley 4-5psi over stock, requires performance tune & shorter belt.
Testing has shown gains of 60+ horsepower.
When running a 2.81" pulley you will need a shorter serpentine belt to keep tight on your blower for maximum boost.