The intake of the 3 gen SHO has been a productive area to find lost HP. The Factory seems well pleased that the car can motor down the byways without a hint of intake noise by virtue of a tuned system of resonators that insure complete silence and zilch performance. This scientifically designed system of baffles pipes air from the area in the front grill to the drivers side fender into the air box which holds the air filter. Early experiments running the car on a dyno jet with no air filter showed an instant 12-13 HP improvement. This got us working on the intake side of the engine.
First the intake system disparagingly called the "saxophone" is constricted in several places and even has a baffle tube to kill any possibility of fresh air getting into the engine. The SHO air box is the same as the one used in the 3.0 L Taurus LX and is also constricted.
The first experiments involved replacing the "saxophone" with a better intake. That left the small air filter which flow only 173 CFM. Theoretically a 3.4 L engine with a 7000 rpm red line at 100% Volumetric Efficiency can use 420 CFM and the factory "saxophone" system gives it about 1/3 of that.
Early solutions involved cutting out the bottom of the air box or drilling the "dirty" side of the air box with a bunch of 1" holes. Either solution helps a lot but be sure you don't damage the air filter or make a hole in the wrong place so dirty air can bypass the air filter.
The entire air filter can be replaced with something with
much greater capacity and less restriction. The factory forbids use of
an oil impregnated air filter but one can be used with great care. (Do
not over oil the air filter which will cause oil to collect on the heated
wire in the MAF and disturb engine calibration.)
Once you are off warranty you can get a intake system from the SHO Shop. It has an adapter plate which bolts on to the MAF with 4 hex head bolts and that holds a cone type air filter which flows about 640 CFM, much more than you need and makes about 5 HP.
To install the new intake you have to remove the old system first. You have to remove the drivers side wheel and pull out part of the splash shield and nose skirt. Remove the "saxophone" and the new system goes in without much fuss. A metal partition with foam seal is provided to keep hot air away from the intake.
Earlier studies by Jim Heaton indicate that the under hood temperatures of a moving 96+ SHO are within 1 degree of ambient. The open system is noticeably louder at curbside and can make a howl at wide open throttle. Ironically it sounds the same, undetectable in the SHO with the windows up.