Mercury Racing 2.5 XS OptiMax Outboard, Page 2

Direct Injection: Next Generation Outboard Performance
Lean and Green: Evaluating Mercury Racing's OptiMax 2.5XS
Article by Greg Terzian
Photos by Maureen Murphy

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Mercury Racing's OptiMax 2.5XS

Rigging included SeaStar hydraulic steering, a Rapid Jack setback unit, and a Livorsi Marine trim gauge.

The Mercury Racing 2.5XS is based on the well-known and proven 60-degree 2.5 litre engine design that has been around for over a decade, with some minor changes to accommodate new systems. This is Mercury Racing’s first replacement for the 2.5 EFI series of engines, and is designed for light, fast performance hulls.

The 2.5XS features Mercury’s advanced PCM 03 microprocessor that can optimize fuel delivery, spark timing, and knock control for each individual cylinder, resulting in maximum performance and efficiency. Unlike consumer OptiMax engines, the 2.5XS features a tweaked air/fuel pressure setting for increased performance, necessitating the use of fuel with a minimum octane rating of 91. Rounding out its high-performance feature list are integrated mounting points on the exhaust adapter plate for mounting aftermarket steering wing plates.

OptiMax 2.5XS Specifications:
Propshaft Rated Horsepower	225 (168 kW)
Full Throttle RPM Range	6100-6800
Cylinders	V-6 (60º vee)
Displacement	153 cu. In. (2507cc)
Bore	3.50” (89 mm)
Stroke	2.65” (67 mm)
Induction System	Direct Fuel Injection
Ignition	Digital Inductive
Charging System	60-amp (846 watt) w/voltage regulator
Gear Ratio	1.87:1 (SM) 2:1 (TM)
Fuel/Oil Ratio	Electronic Multipoint
Recommended Oil	Mercury Premium Plus TC-W3
Required Fuel	91 Octane (R+M)/2 Unleaded or 96 RON
Rotation	Right Hand (SM) (TM)
Shaft Length	20” (508 mm)
Weight	(L) 450 lbs. (203 kg)
Warranty	* See below
* Two-year limited warranty for recreational boating and three-year limited corrosion warranty. One-year limited Mercury Product Protection Plan available.

Port side view of the powerhead reveals the Motorola PCM 03 microprocessor. Also visible is the port side fuel rail and ignition coils.

Removing the cowl of the engine reveals a neatly laid out if somewhat crowded arrangement of electronic components, wires, and hoses. A protective plastic hood conceals the top of the flywheel, compressor, and the serpentine belt that drives the compressor and alternator. The intake plenum is a downdraft design, very similar to that on the 300X.

One area of disappointment is the trim system, which utilizes the integrated three-ram system of its consumer counterparts. This system is just not as robust, nor does it offer the trim range of the single ram high-performance trim systems on the EFI series engines. On the plus side, this trim system proved very responsive, and there are no worries about mounting a trim pump inside the boat. The complete engine weighs in at approximately 450 pounds, which is roughly 150 pounds lighter than an equivalent four-stroke engine.

Page Three: The Test Setup