The car already has more built-in cold air flow capability than the 4.6 (small) engine can handle, and modern panel filters are NOT restrictive. Use a good name brand of pleated panel filter (WIX, Fram, AC Delco, Purolator, PartsMaster, etc.) and avoid using any sort of oiled "filter'. Our MAF is extremely sensitive to oil contamination and is close to the filter panel itself.
Forget aftermarket cutesy "upgrades" - keep it clean and drive it like you stole it. Get deep into the FWD Northstar forums. The lights will come on.
For your pre-2000 (Very different) Northstar, study this......... written by one of the GM/Cadillac Northstar Systems powertrain engineers.
https://www.cadillacforums.com/cadillac-tech.html
If you want to prove or disprove filter flow, use an OBD-II gauge instrument plugged into the test port. Observe MAP - Manifold Absolute Pressure (inverse of vacuum) - during full throttle acceleration runs (your car is speed limited to 112) and use the filter that gives you closest to MAP = MAX. (highest MAP = vacuum ~ 0)
You're fooling with an engine that is a tad smaller than a 1957 Chevy 283. The factory cold air intake duct and the intake manifold are relatively huge for your engine, so atmospheric pressure has no problem pushing air into the engine at WOT.
Please update your
profile - use the other poster login banners for hints. It sure makes diagnosis and advice easier.
