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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Test Results and Impressions

Turning a 34-pitch cleaver, top speeds above 100 MPH were easily obtained with two aboard.

Initial impressions of the engine by veteran drag racer Michael Bates are that the OptiMax has a very unassuming posture created by its extremely refined idle and running quality. There is no mistaking the sound of the air compressor’s churning audio as it works under the cowl.

Acceleration is brisk and impressive while the OptiMax’s broad torque band muscles the large diameter 34-pitch cleaver with authority. After several passes and adjustments to the Rapid Jack setback unit, a top speed of 106 MPH was achieved as indicated by the Livorsi Marine GPS speedometer. This puts the 2.5XS on par with the performance level of the highly-regarded 2.5-litre 225 ProMax. Taking it a step further, the tunnel hull snaps up on plane with the 34-pitch cleaver, and speeds of 100 MPH were easily obtained with four adults aboard - a testament to the Mercury's impressive big-blade turning torque.  Bates feels that with further time on the rig 110 MPH is within the realm of possibility - and we believe him. One observation of particular interest is the rev limiter on the 2.5XS. While technically limited to 6800 RPM, our engine’s limiter kicked in at 7100 RPM. Is this intentional? Officially, no, but Mercury high performance engines have always been known to perform above their stated design limits. That said, our best performance was not obtained that that RPM level.

Putting the boat through maneuvers, the 2.5XS always maintained composure and smooth power delivery.

Although the 2.5XS OptiMax is a two-stroke design, all of the extra systems and the larger 3-litre midsection on the engine add weight, so it is a bit heavier than our high performance 2.5 Offshore. The Triad didn’t seem to mind the extra weight at all though, and handled all maneuvers very well.

The impressive performance of this engine further solidifies our optimism about the future of performance boating.  Mercury currently has several OptiMax engines in development, and judging from the results we achieved with the 2.5XS, they are heading in the right direction with this platform.  While the direct-injected OptiMax does weigh more and turn less RPM than the performance engines we’ve all grown used to, it’s clear that these factors are not the demons that many have feared.

Performance Impressions

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