Whats with Sears H.P. ratings ??

Blade tip speed is regulated by ANSI, therefore the engine RPM must be limited to stay within those tip speed limitations.

A 5 HP engine is rated at 3600 RPM. Therefore, it produces 7.3 ft/lbs of torque at its rated HP RPM.

When the engine is installed in a lawn mower, it is usually goverened down to around 3000 rpm. In this case, the RPM the engine runs at is below its power peak and also below its torque peak.

Greg


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Motorhead, you are right there of course [img]/forums/images/smiles/icon_smile.gif[/img]

I always screw with my springs until I get the MAX rpms my engine will produce with it's carb... Never had one come apart and they rarely die when I cut the really tall grass....

About this new Torque rating and why Sears went with it.... I have no friggin clue, and didn't even know until Greg brought it up...
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On 2007-04-23 07:51, thekingofazle wrote:
If it were based only on blade rpm per cutting speed, you could just put a 4-tine blade on it, then each blade will cut less.

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Notice I didn't say grass cut per blade pass, I said grass cut per revolution. Double the number of blades, means each blade only has to cut half as much because you have twice as many blade passes and a constant walking speed, so you end up needing the same amount of hp/tq.

Greg's info on the RPM limit is interesting and makes sense, as I figured there had to be an RPM limit for off-the-shelf lawn mower blades.
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You could also sharpen them to a razor finish.

But I guess now I'm grass-ping at straws.

Or just replace them with freakin lasers, then it wouldn't take any HP!
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