How do they rate HorsePower (now and then)??

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feathercrafter

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I have a 1986 Mercruiser 3.7L 190hp I\O. Can anyone please tell me how ther rated the horsepower back then and how they do it now, (at the prop, crank, or flywheel)? and if, by todays standards my motor is actually higher or lower in hp than its orig. rating?
 
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wakatoa

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Re: How do they rate HorsePower (now and then)??

I believe that in earlier years horsepower was measured at the fly wheel but is now measured at the prop. Not sure when the transition took place or what the difference would be.
 
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feathercrafter

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Re: How do they rate HorsePower (now and then)??

OK, now that you have gotten me hooked on that web site, lets cut to the chase: IF we had 2 motors both rated 190hp, one was measured at the flywheel and one was rated at the prop, WHICH motor would actually be HIGHER if you took them both and measured them the same way???
 
62_Kiwi

62_Kiwi

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Re: How do they rate HorsePower (now and then)??

The one measured at the prop would in fact be the higher powered motor.<br /><br />A reading of HP at the flywheel would be higher than HP at the prop on the same motor - due to losses in the drive train.
 
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feathercrafter

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Re: How do they rate HorsePower (now and then)??

Exellent and correct answer. Here is what I just found: There are two specific places to measure horsepower: Brake Horsepower (BHP) is the horsepower at the engine flywheel while Shaft Horsepower (SHP) is the horsepower at theshaft, i.e. after it goes through the transmission/ reduction gear. There is generally a 3-3.5 % loss of horsepower as it goes through the transmission.Usually comparisons focus on BHP. Thanks All!
 
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skier

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Jan 31, 2002
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Re: How do they rate HorsePower (now and then)??

Is that for automotive engines or marine engines???<br /><br />I was told that everytime a drive shaft takes a 90 degree turn you loose aprox 10% :confused:
 
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Lark40

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Oct 29, 2001
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Re: How do they rate HorsePower (now and then)??

The drop for automobile engines was about 25% when that industry made the ratings switch for the 1972 model year.<br /><br />So, the 3% reduction noted above sounds low to me.
 
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ODDD1

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Jan 23, 2001
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Re: How do they rate HorsePower (now and then)??

the typical loss for a stern drive is 8 to 10%....marine stuff changed around 1988?....the '190'designation was generous at best...dont get me wrong, I like these 3.7's.....just that 180 was a more accurate assesment...
 
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