Re: Super / Turbo Charged Outboard
Couple of things you need to remember:
1. Two cycle engines have an effective displacement of about 66% of the displacement computed by bore and stroke. That is why a two cycle engine of a given advertised displacement delivers only about 2/3 more power rather than twice the power of a four cycle of the same displacement. (two cycle has twice the power strokes so you would expect twice the horsepower).
2. Because the bypass and exhaust ports are on the same plane, the cylinder effectively goes to atmospheric pressure when both are open.
3. The piston can only suck into the crankcase a MAXIMUM of 2/3 the advertised displacement. With reed valves, because of the resistance of opening the reeds, the effective pumping becomes less. Low boost supercharging can increase pumping efficiency but in the case of small two cycle outboards, the premium paid to run the supercharger will probably offset any horsepower gains.
4. You can supercharge, but anything in excess of 2/3 displacement will simply blow out the exhaust ports. In fact, on naturally aspirated racing engines, some of the fresh charge will blow out the ports anyway. THAT is why many small racing engines are run on tuned pipes. Go over to scream and fly and look at some piped "Hot Rod" engines.
5. Thus: Supercharging will be a very costly and inefficient way to TRY to gain more power. Port work, tuned pipes, aftermarket reeds, carburetion, and carb velocity stacks are the best ways to increase horsepower.
In addition, if your engine is a Force as alluded to above, it is dirt simple crossflow, old-school design. Don't expect too much from it. That is just basic design physics.
And remember too: If the supercharger is mounted before the carb and you use a high boost, the pressure will decrease the amount of fuel delivered by the venturi. The carb needs to be mounted on the supercharger intake. All in all a complex job.
