Ignition. The process by which a spark ignites the air and fuel mixture inside the cylinders, has long been one of the Achilles' tendons of gasoline marine engines. Why? Well, although boats mostly run at cruise speed while traveling towards their destination, they still spend long periods at slow or idle speeds. Traveling through marinas, channels and other slow or no-wake zones requires an ignition system that is both powerful and accurate, so that all fuel is burnt and enough power is generated. Traditionally, however, just the opposite happens, as the ignition sparks don't last long enough to burn all the fuel and combustion becomes erratic. The engine sputters and, in many cases, stalls. We don't have to explain the potentially catastrophic effects of a stall while docking in tight spaces or traveling bow-to-stern in busy traffic. This poor ignition also fouls the spark plugs (coats them in unburnt fuel), which then also underperform at high speeds, dramatically increasing fuel consumption and engine load, while decreasing actual power output.
Medusa has solved this issue with a combination of features that work together to deliver flawless slow speed performance, delivering rock steady RPMs with NO stalls. Indeed, Medusa delivers the same precision as a diesel when docking, trolling or traversing crowded channels, and like a diesel, it is ready to jump out of the hole and get on plane lighting fast. And we can achieve this not only with our fuel injected engines, but with our carbureted ones as well, with the same ease and repeatability. How have we accomplished that seemingly impossible feat?
- Ignition System. First is our ignition system, made by a company whose name, Multiple Spark Discharge, or MSD, says it all. Medusa engines are fitted with an MSD 6M-2L ignition box that is the heart of the system. The MSD ignition is unique in that it uses capacitive discharge (CD) for very powerful sparks, and under 3000 RPM, it fires multiple sparks every 20° of crank rotation as opposed to just one on traditional systems. This ensures complete combustion of the fuel/air mixture, increased power, excellent throttle response, improved fuel economy and no fouled plugs. The MSD box also allows us to impose a 5000 RPM limit on our engines for protection against over-revving. The 6M-2L box is then connected to the MSD 8560 Marine Distributor, which is completely sealed against the elements and boasts a magnetic pickup and precision reluctor for stable trigger signals throughout the whole RPM range.
- Camshaft Design. Then comes our choice of camshaft profiles. Our hydraulic roller Howards camshafts are chosen for their short duration which literally eliminates valve overlap, a condition where both intake and exhaust valves are open at the same time, leading to very rough idle and, in many cases, stalls. The lack of overlap allows for very clean combustion since no fresh fuel and exhaust gases are mixing in the chambers.This, coupled with the multiple sparks of the MSD ignition ensures that all the fuel in the cylinders is burnt, allowing the cylinders to actually empty out in between cycles. This combination yields a very strong, reliable idle for steady power at low speeds. Since the exhaust gases are not mixing with unburnt fuel, the emissions are much cleaner too, even in the carbureted engines, a very welcome by-product that helps the environment and is a must for those boaters who water ski or wake board behind their boats.
- Low End Torque. Lastly, there is the famous Medusa torque. All other gasoline engines suffer from weak torque on the low end, which further aggravates the situation since low speed navigation is usually done in channels with strong currents or while trolling in heavy seas, and when the propellers don't have enough torque to counteract such conditions, the increased resistance slows down the shaft rotation, greatly compounding the erratic idle and overheating the engine. Think of running a car with the parking brake on. Our diesel-like torque band solves this problem, feeding the propellers enough power to turn at the intended rate, even at very low RPM in the harshest of conditions. This steady low end power constitutes the optimal setting for the ignition system components to work at their best, crisply, precisely and without added stress.