I was interested in this until I saw these dyno results on the MB site...Can anyone explain the hp loss with this mod?

Run # 1 - WITH SL55 Y-Pipe (004.drf)

274.45hp / 284.13tq

Run # 2 - WITH SL55 Y-Pipe (005.drf)

273.47hp / 282.60tq

Run # 3 - W/OUT SL55 Y-Pipe, stock (007.drf)

283.29hp / 289.30tq

Run # 4 - W/OUT SL55 Y-Pipe, stock (008.drf)

280.77hp / 283.83tq