Low Stress Performance

Motors can work fairly easy or have a tough time performing their duty. The stress imposed on an engine makes all the difference in terms of performance and durability. Marine engines are further affected by running near WOT (wide open throttle) for the majority of the time and having very poor ventilation inside the cramped confines of an engine bay. Thus, one of the most important goals facing the marine engineer is to design an engine that runs under minimal stress, unless of course, we don't mind the engine breaking down every 2-3 months and needing to be replaced in 4-5 years' time. Achieving this low stress performance requires a careful exercise in balancing the engine architecture, the quality and profile of its components and the know-how to find performance gains in areas of low impact. At Medusa, this is how we build engines that obliterate the competition but don't break a sweat doing so:

Compression Ratio or CR. The ratio between the pistons' travel inside the cylinder, from absolute bottom to the absolute top, once the fuel/air mixture has been compressed to the max, is referred to as Compression Ratio. The higher the CR, the more energy will be created during the combustion phase and the more power released, so all other factors being equal, any engine will produce more power with a higher CR without increasing its displacement. This is the method by which modern cars reach high efficiencies with such small engines. But high CR comes wit problems of its own. It increases the loads on the engine exponentially by creating more heat and pressure, which leads to metal fatigue and premature failure. Another problem is that high CR does not like low octane gasoline, like 87 octane, and when the two mix, “knocking”, or detonation occurs. If detonation goes on long enough, the engine will suffer from catastrophic destruction. That is why diesels, which run at very high CR, are so heavy and massive, since their every component is 2-3 times the thickness of gasoline engines. But still, high CR gas engines are not built to the same standards as diesels, which is why so many of them begin to exhibit signs of structural weakness not long after their 2 year warranties have expired.

So we went the old way and designed our engines with low CRs, ranging from 8.8 : 1 to a maximum of 9.5 : 1, which assures us of very light loads on the engine's rotating assembly, even if our components are capable of withstanding very high CRs given their racing nature. Look at it as a double insurance. And of course, we now have the ability to use 89 octane fuel or even 87 octane, without any problems whatsoever, even if the pump at the marina claims 92 octane. And though our low CR might suggest lower power, we have compensated for that by ingeniously engineering Medusas so that, in fact, we beat every other engine out there in both torque and horsepower.

Normally Aspirated Induction. How the air comes inside the engine to be mixed with fuel makes a big difference in the engine's power output. The more air can be inducted, the more oxygen can mix with fuel and the better combustion is achieved. To that end, manufacturers have striven for decades to enrich the air/fuel mixture through the use of forced induction systems like turbochargers or superchargers, which force pressurized air into the combustion chambers. But once again, those systems greatly increase the stress by generating more heat and add a tremendous amount of complexity, size, weight AND cost. In our opinion, complexity is the last thing a marine engine needs, so we stayed with the true and tried method of normally aspirated induction, where the carburetor or fuel injection system simply use the surrounding air at normal atmospheric pressure. Yes, this is more inefficient but it is far easier on the engine, and again, based on our power figures, it is easy to see we do not need pressurized air to deliver the highest output out there.

Camshaft Design. Our hydraulic roller Howards camshafts are chosen, among other features, for their short duration, which means both intake and exhaust valves open for a very short time. Then, the rocker ratio that determines the length of the valve opening is a low 1.5, which means the valves are only pushed upwards into the open position for a short distance. Both of these features greatly reduce the stress on the valve train, which traditionally is the hardest working, most-prone-to-failure component in a high performance engine.

By combining these features we have achieved an engine that runs well below its maximum potential for long lasting life and reliable operation, while delivering performance figures that are unmatched by its competition, engines that boast combinations of very high compression ratios, forced induction systems and highly aggressive camshaft profiles. Because intelligent engineering is not about achieving the most with the most, but about achieving the most with the least.