HP Measured Where?

[gtx4]

Why Are some motors Horsepower measured at the crank and some at the Prop? Mainly Talking About Evinrudes. Did they change there method in a certin Year? i.e. the 175 hp is that the same as the 235 hp?.<br />Any help?

 

[JB]

Re: HP Measured Where?

Howdy GTX4. Before the mid seventies engine hp was measured at the crankshaft. Since the early 80s it has been measured at the prop. I don't know what years the changeover started or finished, but since then all engines have been measured at the prop.<br /><br />The 175 is not "like" a 235 except in appearance. There are important differences inside.<br /><br />Red sky at night. . .<br />JB

 

[grandx]

Re: HP Measured Where?

HP should have always been measured at the prop, but wasn't. Who cares what the HP is at the power head if you lose 20% tranferred to the prop. It seems they have got it right now. I've heard in the past that a rule of thumb (for Mercs anyways) that the older ratings can be dropped by 15-20% to determine the HP rating at the prop. i.e. an old rated 235 is somewhere between 185 and 200HP at the prop. For what it's worth, I'm sure it's different for each manufacturer.

 

[Dhadley]

Re: HP Measured Where?

OMC converted to propshaft ratings in 1984. The 175/235 thing is interesting. Both models in the 160 ci form were pretty similar in output. One was over rated and one was under. Both conformed to NMMA's rules for advertised horsepower vs actual.<br />The 2.6 XP/GT (ported and scolloped) 160 ci motor was somewhat more powerful.<br /><br />Good luck!