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Posts: 152
| Without knowing the bore and stroke of each engine I can only guess. The Yamaha could have a more oversquare engine that lets it rev higher. The more times a piston goes up and down per minute, the more often it is getting fuel into the cylinder. As I stated before, 4,700 ft, per second is maximum safe piston speed. A Harley is on the edge at seven grand where a Yamaha crotch rocket is able to pull twelve grand before it reaches the 4,700 ft. per sec.. The Harley makes a ton more power below six grand, but looses the peak power battle becouse the Yamaha can rev higher and pack more fuel in. Other factors are the compression and what type of carburation are used. A two stroke uses the placement of the intake and exaust ports in the cylinder to control the power band. It is very hard to get a two stroke to make good power from low to high r.p.m. becouse of the limitations of the port placement. A larger displacement would overcome a lot of these problems. You could still have 90 hp and better low end power with a larger displacement like the Johnson. With outboards this is not generally a problem becouse we are most often running at half to full throttle. Exaust tuning is critical in two strokes for maximum power and to determine the powerbands characteristics. That gets into ultra sonic waves that scavange buned gas and help bring fresh gas in. I would like to see Dyno printouts on each of these engines. When I lived in the South West the 300 ford six was used to run irrigation pumps and they would last longer than any V-8 with a larger displacement. The only thing better was the old Moline engines, but it got to the point you couldn't get them. Inline three's balance pretty well, I have a inline three Merc and it is very smooth. It's good to have choices! Is this a great country or what! Later | |
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