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Originally Posted by pjard
A bit off topic but my 115 Mercury will run about 6200 RPM's at full throttle. That equates to 413 RP Second....it's amazing to think about it. It boggles my mind that thing doesn't just explode! What a machine!
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It's all about piston speed (the distance the piston travels over time, or the stroke in feet x 2 x RPM). Most marine engines are designed to run at 3000 feet per minute of mean piston speed. High-performance street engines typically run up to 4000 FPM. Racing engines run way over 5000. Stroke and RPM are the key components to piston speed, the shorter the stroke, the higher the RPM can be for give piston speed. The engine in my motorcycle has a 4000 FPM piston speed at 12,000 RPM. It'll do that all day. My boat would hit 4000 FPM at only 6000 RPM and it would not last long doing that (if it were even possible).