The 1998 Pontiac GTP supercharger uses
GM part number 12345347 or an equivalent synthetic motor oil with the
SAE 5W-30 viscosity rating. Do not use anything other than a synthetic oil specifically designed for supercharger applications. Using the wrong oil can severely damage the supercharger.
It's crucial to check your owner's manual for the most precise and up-to-date information on the recommended oil type and capacity for your specific vehicle. The manual will also detail the proper oil change procedure for the supercharger.