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Never fiddled with 4-stroke propping before and I have a question.
On the merc 25 EFI 4-banger, the manual says RPM range is 5000-6000 RPM.
I had an 11" pitch prop, ran about 31mph, but with just me on the boat and normal load, it revved up to about 6180 rpm which getting pretty danged close to the 6250 rpm fuel cutoff. And is above the reccomended RPM range.
I switched to the same brand, same diameter 12.5" pitch prop, and the speed went up slightly, maybe 1 mph. But my RPM's dropped drastically to mid 5500's max, most of the time I'm in the high 5400 range.
Not sure how I lost all that RPM with just 1.5" of pitch change; I thought the school on props is 200 RPM for every inch of pitch??
Anyways, here's my question: is it better for 4-strokes to run close to the max RPM's as a 2-stroke would, or is it better to have them lugging along?
-T
On the merc 25 EFI 4-banger, the manual says RPM range is 5000-6000 RPM.
I had an 11" pitch prop, ran about 31mph, but with just me on the boat and normal load, it revved up to about 6180 rpm which getting pretty danged close to the 6250 rpm fuel cutoff. And is above the reccomended RPM range.
I switched to the same brand, same diameter 12.5" pitch prop, and the speed went up slightly, maybe 1 mph. But my RPM's dropped drastically to mid 5500's max, most of the time I'm in the high 5400 range.
Not sure how I lost all that RPM with just 1.5" of pitch change; I thought the school on props is 200 RPM for every inch of pitch??
Anyways, here's my question: is it better for 4-strokes to run close to the max RPM's as a 2-stroke would, or is it better to have them lugging along?
-T