[staylor]

...holding the HP on a specific high performance model to the upper end of the allowable rating band- a "plain" 150 would be 150 and the special motor would be 160 or so but still within the allowable ratings band- which I believe is still plus or minus 10% under specified testing conditions. In this case- I would check with the dealer as to the type of intake reeds running in the XS. I've heard they that all the XS motors run fiberglass reeds, vs stainless steel for the regular motors. Other changes involves fuel system settings, ECU mapping, timing, etc, to sqeak out a few extra horsepower within the ratings band. Typically there will be a note in the motors warranty that broken glass reeds are not covered, since reed replacement is a "maintenance item". Another trick you can play with glass reeds is to set the reed stops out a bit higher to allow more reed travel for a bit more power- and Merc may be doing this on the XS. In any event, fiberglass reeds are not known to last as long as steel reeds, and changing reeds on a modern DFI engine is not a job for the typical owner- nor many marine mechanics- and its not cheap.

But what the heck- you have to pay to play if you want the last mph out of the rig.
Doug