How do they get a 2.5 powerhead on a 3.0 mid? --All in the adapter plate? If so, yes a 2.5 powerhead would need a different adapter plate, different L.U.
Performance #s on that 200 ros? different thread?
This is all I could find on the 2.5XS.
Mercury Racing Releases All-New OptiMax 2.5XS Outboard
July 29, 2004
FOND DU LAC, WI. – Mercury Racing is pleased to announce the release of the all-new OptiMax 2.5XS outboard. Designed for smaller, lightweight boats (flats, bass, vee bottom and catamaran sportboats), the custom-built engine features a compact 2.5 liter, V-6 OptiMax powerhead mounted on a 20-inch, 3.0 liter center section and gearcase. The compact V-6 powerhead saves weight on the overall package, enhancing boat performance and fuel economy.
It is the first of next generation low-emissions outboards to replace the legendary 2.5 EFI Series, which will be discontinued at the end of the 2005 model year. The direct fuel-injected powerhead is full of race-inspired features including Mercury Racing pistons, cylinder heads and air intake system with carbon fiber reeds. The Mercury exclusive PCM 03 microprocessor provides the ability to optimize fuel, spark timing and knock control for each cylinder independently, enhancing engine running quality and performance. The PCM 03 also operates the electronic multipoint lubrication system. The SmartCraft Control Area Network (CAN) system, a network of sensors and actuators, proactively monitors and controls multiple engine functions. This system also enables the PCM 03 microprocessor to provide real-time engine function data to accessory SmartCraft gauges, including speed, RPM, engine trim level, fuel consumption and range.
Unlike other DFI systems, OptiMax uses an exclusive 2-stage process. A burst of air (at 90 psi) shoots through the fuel, breaking it into a fine mist. This fine mist creates more surface area for combustion and stays suspended in the cylinder longer, resulting ina more consistent and complete burn. The 2.5XS features a higher air/fuel pressure differential than production engines, enhancing running quality.
The 2.5XS features an exhaust adapter plate ,built-in appendages for mounting after market steering wing plates. Models come with the new Mercury Racing rigging tube kit. The kit features a larger 2-1/2-inch size for fitting all electronic cables, steering cables and fuel lines. The durable hose threads onto the one-piece couplers - providing a complete seal at both the engine and boat.
Models are available with a 20-inch (508 mm) center section and either a right-hand rotation 1.87:1 Sport Master gearcase or 2:1 Torque Master gearcase. The OptiMax 2.5XS comes with a 2-year warranty and a 2-star CARB emissions rating.