After talking with the shop owner (who has a few turbocharged stangs, a 9sec blown 05 stang, and experience with several supercharged cars), he says that the shape of the stock Y-Pipe points the air into the blower better than the SL55 setup. He did say that the SL55 Y-Pipe has more volume - so it will possibly help on a car with a pulley setup.

He also said that, obviously, the Y-Pipe is not the major restriction on these cars (which is hard to believe by looking at it).

For the record - I ran the SL55 Y-Pipe first, so the engine/IC temps should've been cooler. Still made less power.

Interesting either way! But, I posted honest results, at least!

I also plan to try it at the track, both ways.

Without being able to open the throttle up through the whole dyno run because it would down shift...we could be missing a low-end gain over the stock pipe. Although the peak power is less, the low end may be what makes it 'feel' faster out of the hole and around town. The track should show this in the 1,000 ft and times/speed, 1/8mile, etc.

Otherwise, I could've been mistaken about the 'noticeable' gain due to the fact that you can hear the supercharger much more and you can hear the intake better.

SQ