Editors Note: While walking the docks at the 2020 Miami Boat Show, I noticed there were Mercury Racing engines everywhere.  I asked my friend Steve Miller from Mercury Racing to share his insights into what goes into a Mercury Racing engine vs. a standard outboard motor.

At some point in their lives, just about everybody wants to go fast.  Feeling the rush of the open air while listening to the roar of perfectly tuned engines. The thrill of living on the edge as the world flies by while the speedometer keeps climbing.  Just you, your boat, and the horizon. We’ve all longed for that adventure.  But going fast on the water is a lot more than just tuning up an engine and putting the sticks down.  A lot goes into designing a performance outboard, far more than just delivering the big number on the speedo.  An outboard designed for high-performance boat operation today also focuses on optimizing boat handling and believe it or not . . . reliability and durability.  Today’s modern performance outboards are delivering these attributes more than ever before.  But to truly appreciate what we have today, it is worth a quick look back through time to appreciate how far the technology has advanced and why so many more boaters are able to embrace their inner speed genes.

Evolution of Performance Outboards

There was a time many years ago where boaters who craved speed had to make some significant compromises to really go fast.  First, high performance outboards in their 2-Stroke infancy were loud.  Their full throttle RPM range was quite a bit higher than the average consumer outboards of the day, and they often used light-weight cowling with little to no foam dampening to absorb the added decibels.  The oil mixture was usually richer than a typical 50:1 2-Stroke consumer outboard, so boaters had to contend with the added consumption and cost of the high-performance oil.  In the early days, the oil had to be manually mixed with the fuel, and the engine oiled at a constant rate, so the smoke level at idle speeds was higher. These engines also required higher octane, premium fuel or in some cases expensive race fuel.  Finally, performance outboards were bred from competition racing engines. As such, they were never intended to do a lot of idling or lower speed operation, which meant running quality was not as smooth as the average consumer outboards of the time.

Performance outboards in those days would also have solid mounts, which meant more vibration was noticed in the boat versus a conventional outboard which had rubber mounts.  Special gearcases that were designed to run in a more surfaced state were combined with high performance propellers to deliver the handling traits required to go fast.  In the early days, most of these outboards were found on 16’-22’ single engine boats which were essentially the street rods of the lakes and rivers, so precise cornering and handling was critical and therefore many of these boats also used special steering systems designed specifically for high performance boating.

In short . . . if going fast on the water was the goal, a lot of concessions had to be made to do it properly and as safely as possible.  If the technical trade-offs weren’t enough, most high-performance 2-Strokes at the time carried a very limited warranty, often around 90 days.  Even though many boaters in those early times would have liked to have experienced the thrill of higher speeds, these concessions would ultimately prove to be too numerous to accept for all but the most extreme enthusiasts.

Modern Performance Outboards

Fast forward a few decades to today’s performance outboards, where the advancements in engine technology have made it possible for more boaters wanting to experience the thrill of high-performance boating to do so without having to compromise on creature comforts. Today’s high-performance consumer outboards are 4-Strokes, which by their very nature make them much smoother and quieter than the 2-Strokes of days gone by.  They have separate lubrication systems, so there is no oil and fuel to mix and thus little to no smoke.  All of this means the base platform by which a high-performance derivative is created will ensure a much smoother and more well-mannered engine at lower speeds and during idle periods.

Supercharged Power

But how does one get a 4-Stroke to perform?  The first high horsepower 4-Strokes were larger and much heavier than their 2-Stroke predecessors.  By design, a 4-Stroke takes twice as many piston cycles to perform the same cylinder operations a 2-Stroke does (intake, compression, ignition, and exhaust), and it is inherently heavier from the addition of valve trains, oil sumps, coolers, etc. It took a lot of learning in the marine industry to overcome these challenges, and ultimately it took a supercharger to do the trick on the highest horsepower models.  A supercharger essentially compresses, or boosts the ambient (surrounding) air before it enters the engine, which increases the intake air density, or as engineers like to call it, “mass air flow”.  Higher mass air flow means higher power output and therefore better performance.  To further improve efficiency, the compressed air from the supercharger passes through a charge air cooler prior to entering the engine, cooling the air and further increasing air density and power.

Other Engine Modifications

In addition to supercharging on the largest performance outboards, modern 300+ horsepower performance outboards have had further technical refinements to deliver greater top speeds beyond conventional 4-Strokes, even in naturally aspirated (non-supercharged) configurations.  Today’s performance outboards typically feature unique intake manifolds, often with shorter runners.  When combined with custom intake cams, the engines breathe more efficiently and create additional power output.  Calibrations are optimized for performance and typically involve increasing the full throttle operating range which not only increases horsepower, but also allows for more efficient propping.  This provides a significant benefit for lighter-weight performance boats with hulls capable of higher speeds.  Where in years past most high-performance outboards required at least premium pump fuel of 91 octane, today’s engines are optimized for readily available and lower cost 89 or even 87 octane fuel.  But making power is just one aspect of creating a high performance outboard.  Most seasoned performance boaters will tell you that getting to that big top speed number is one thing, but feeling the boat accelerate and respond immediately when throttle is applied is a huge part of the experience.

Digital Control Systems

Let’s face it, there are days on the water when conditions are just not favorable for running up to full speed on a fast boat . . . at least not pleasantly.  A 90 MPH boat, however, will cruise easily at 50, 60, or even 70 MPH, so having fun on the water is not entirely out of the question.  On days like these, having that instantaneous throttle response makes the boater at one with the vessel, and delivers an experience similar to a roadster navigating tight corners and feeling the satisfying pull as more throttle is applied.  Many of today’s high performance 4-Strokes feature digital control systems that replace conventional mechanical push/pull throttle and shift cables with a data cable from the helm to the stern.  These control systems interface electronically with the ECMs (electronic control modules) on the engines and instantly take advantage of the higher RPM range to plane off quickly and provide powerful midrange acceleration.  With electronic control systems, every bit of user input to the throttle is immediately felt, and that’s something a boater can enjoy every day on the water.

Stiffer Engine Mounts

While power development and responsiveness are critical to achieving the high-performance driving experience, it would be virtually impossible to optimize boat handling without tuning the engine mounts to deliver precision steering control.  Since most performance boaters are not actually competing in races, it is typically not necessary to use a full solid mount system, which tends to transmit more vibration to the boat.  Instead, most consumer performance outboards today use harder durometer (stiffer) rubber mounts, which are tuned to strike a balance between delivering optimal steering feel and control while minimizing felt vibration in the boat.

Modified Gearcase

While mount systems play a critical role in ensuring proper boat handling at higher speeds, the gearcase design is the other major factor in achieving the full precision driving experience on a performance outboard.  In many cases, boat speed is optimized on the fastest hulls by running the engine higher up on the transom.  In doing so, the gearcase will run in a partially or even fully surfaced state, depending on the specific application.  With less gearcase in the water at speed, hydrodynamic drag is significantly reduced, and this becomes yet another lever to optimize top speed.  It’s important to note that with performance boats, and especially ones capable of 90 MPH or more, a standard gearcase will not be able to operate in this manner.  Instead, a gearcase such as Mercury Racing’s Sport Master is needed.  A Sport Master gearcase uses a longer torpedo with a crescent style leading edge and a pointed nose with low water pickups.  This combination allows a fully surfaced running state while still providing ample cooling to the engine.  The long torpedo length reduces potential for blowout by minimizing cavitation bubbles flowing back toward the propellers, and a longer skeg below the torpedo ensures proper handling and boat control at speed.  On single engine applications, the skeg is typically cambered, or at a slight angle to help offset steering torque.  These types of gearcases work best on lighter, faster hulls that can generate lift on their own and require minimal trim.

More Than Just Power

Developing a true high-performance outboard is much more than it may seem on the surface.  The technical differences are many between an outboard designed for performance boating vs one intended for powering a fishing boat or runabout, and they span the entire outboard from the powerhead to the gearcase.  A tremendous amount of knowledge and experience with high-speed boat setup is required to design an outboard that is not only fast and responsive, but also delivers precision handling, reliability, and durability in the proper applications.

If you are a boater and feel the need for speed, I cannot emphasize enough the importance of seeking out a reputable boat builder or dealer with experience in properly setting up the boat.  Proper boat setup from helm to stern is critical for boating at speed safely, and it is much more involved than simply bolting the outboard to the transom. Align yourself with a true setup expert, do your homework to identify your needs for your particular application, and take the time to learn your boat’s handling traits and limitations and you will enjoy the thrill of high-speed boating for many years to come.