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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The Test Setup

The relatively lightweight 2.5XS is a perfect match for light, fast performance hulls. Performance on our Triad tunnel hull was impressive.

For this test, we teamed up with Ocean Outboard and Ocean Marine of Freeport, New York. Ocean Marine and Ocean Outboard are ideal partners for this evaluation, having collectively accumulated six world titles in powerboat racing as well as numerous kilo records.

When I met with Paul Balabus and Jim Molnar back in December, we discussed the performance potential of a Mercury OptiMax 2.5XS on a light tunnel hull. Could this engine provide 100 plus MPH speeds reliably and efficiently? One thing is for sure, direct injection technology is here to stay, and for those have no interest in running a four-stroke outboard, this is the only other choice.

For this evaluation the new Mercury 2.5XS OptiMax was mated to a 2005 Triad STV Euroski tunnel boat. Head mechanic Jim Molnar and Brandon Balabus rigged the engine and set up the boat, installing six inches of setback and the almost-mandatory trim indicator. Molnar and Balabus opted for Livorsi Marine gauges; however the 2.5XS would also be a perfect match for Mercury’s SmartCraft system. Although the 2.5 litre OptiMax engine is RPM-limited, this would not pose a problem since torque is something that the OptiMax platform has no short supply of.

Torque to spare - the OptiMax 2.5XS delivers a very broad torque curve.

Several propeller styles and sizes were used for this evaluation, finally narrowing our selection for top speed down to the tried-and-true Mercury Racing Lab Cleaver, 15 x 34P. This propeller size is somewhat unusual for a rig this light, yet it was an ideal match for this engine’s very broad torque curve.

The 2.5XS is equipped with the 3-litre version of the SportMaster gearcase using the 1.87:1 gear set, as well as a 20-inch midsection (no short shaft version of this model is offered) that is equipped with solid mounts for high-speed stability. Additional exhaust relief passages further distinguish this midsection from the consumer offerings. Some have questioned the use of the 3-litre SportMaster for this engine, citing a size difference and resulting loss of performance potential. However, careful measurements reveal the case dimensions are exactly the same as its 2.5-litre counterpart.  The 2.5XS is also available with Mercury's TorqueMaster or FleetMaster gearcases to suit a variety of performance setups.

Page Four:  Test Results and Impressions