2 Vs. 4 Stroker
Brian,
Here in CA we have some of the toughest pollution regs and 2 strokes are pretty much banned on most lakes and are being phased out all together in the state due to the issues mentioned.
4 Strokers are more efficient and environmentally friendly, but that comes with a weight penalty as 4 strokers are heavier than 2 strokers since they require a cam + valves, fuel injectors, etc.
As for fuel economy at which RPM and stroke type, that's an individual relationship to boat, engine maintenance, prop size, weight, bottom cleanliness, etc. But I almost certainly a 4 stroker is more fuel friendly, but you'll have to look up each model's specs and compare. But as Art mentions, dumping raw fuel out the exhaust can't be better in the efficiency dept. The idea was to use the oil/fuel mixture to lubricate the engine's components and as a result, a lot of fuel was wasted as more fuel + oil was ingested than necessary to make sure all the wear surfaces were being lubricated. I can recall in the 1970's when those models smoked like a wet newspaper until warmed up. Plus many folks just dumped in the 2 cycle oil into their gas tanks willy-nilly until the oil metering tank was invented which helped alleviate over/under lubricating the gas. My Uncle holds the patent on that device.
As for noise, outboards in general have queited down but I can't testify to one being quieter to the other as each model may be different (i.e. Honda Vs. Mecury, etc.) but both types tend to dump the exhasut gas through the prop or underwater.
As for maintence, you now have an oil sump and some extra components on the 4 stroker (cam, valves, etc.), but all in all, I think there's probably no more appreciable difference over one than the other, but again, each model may vary. In addition, a 2 cycle was working harder to produce the same HP as the 4 cycle as every stroke on a 2 cycle was a power stroke compared to a 4 cycle, which again, is another weight penalty issue for the 4 strokers - not much, but it;s there. I suspect that will change as technology progresses.
I can testify that in the diesel world, other than the massive ship engines such as the Mann B&W 60,000 hp and up engines, one is hard pressed to find any 2 stroke diesels manufactured anymore. The vernerable Detroit Diesel 2 strokers are gone as their pollution and fuel economy was way outdated by modern tecnology.
Hope that helps
John M.
