hp ratings

[rbringo]

I've read on some previous posts that hp ratings changed in the early 80s. I had a '74 Merc 80 hp but we are looking to replace it. Is a newer ('86) 75 hp equivalent to the '74 80 hp or should I look for a larger one? <br /><br />Thanks everyone. This is a great site.

 

[Navigator]

Re: hp ratings

rbringo,<br />A 74 80hp would be roughly equivalent to a 65-68 hp "1986" engine. The 75 should give you more grunt than your old 80.<br /> <br />As to your Larger question. It really depends on what boat you're putting the engine on. It it was an old boat and was rated for 80 hp, then the newer 75 might be overpowering the boat and make it dangerous. The transom may not be strong enough for the extra power. Although you are not talking about a serious "leap" in power, you're probably Ok. Check your ratings just to be safe.<br /><br />Nav.

 

[rbringo]

Re: hp ratings

Thanks Nav. The hp difference is much larger than I thought. '74 Our Starcraft SuperSport is rated for an 85 hp motor, and the transom has been recently rebuilt. It sounds like a 75 hp would be as big as we'd want to go.

 

[Johnshan]

Re: hp ratings

K heres what my experience is. <br /><br />Took my '85 Mariner 30 hp engine with perfect compression, engine in very good shape. and put it on a friends boat (1960<br />s glastron) rated for a 50 hp. It performed the same as his 1959 yes you read right- 1959 35 HP Evinrude. <br /><br />We noticed no top speed difference, or planning out difference. <br /><br />So whats the story with this? Shouldnt the mariner been like day and night?<br />-John

 

[rbringo]

Re: hp ratings

After reading a few old posts, my guess is that the larger the motor size, the greater the difference will be from the older ones. i.e., the difference will be much more noticable in a 100 hp new vs. old than a 20 hp new vs. old. Maybe some of the more experienced people on this board have further insight...

 

[mbb]

Re: hp ratings

It could be a big difference, or none at all. In older small motors, they may be considerably heavier than a comparable newer one also.<br /><br />The leeway in motor ratings being +/- 10% alone throws a wrench into it. Most motors today make at the upper end of their hp rating limit, but some noticeable ones in past made close to or below lower limits. 140hp evinrudes that were only good for 125 ponies, 150 force only good for 130 or so. <br /><br />This became issue when merc started losing races to yamaha in late 70's. Yamaha was rating at propshaft where domestics were rating at powerhead, so merc downrated their engines too. 150 became 140, 140 became 115, 115 became 90, etc. Eventually industry standardized on propshaft rating with 10% tolerance. But even today a 200 hp can make between 180 and 220 and still be a 200.

 

[prplhze65]

Re: hp ratings

THIS IS TO JOHNSHAN. THINK ABOUT IT. A 42 YEAR OLD MOTOR PROBABLY ISNT OPERATING UP TO ITS FULL POTENTIAL.

 

[evin300]

Re: hp ratings

For better comparison you would have to make sure that both motors had the advantage of the optimal propeller, there is that propeller word again!

 

[JB]

Re: hp ratings

Gosh, wouldn't it be easier if individual engines all met the advertised hp rating in use at the time. They didn't then and they don't now. Some exceeded the rating, some fell a bit short. Even today, even Yamaha, which most agree are as well-made as any will differ. Ten 150's will offer 10 differing peak hp figures. The differences may be in fractions of a percent which makes them trivial, but how big are the differences you guys are tossing about and how much REAL difference do they make?? Get an engineer to explain to you how unreal horsepower ratings are and how torque over a wide rpm range applied to an optimum prop is what makes boats go. <br /><br />Red sky.<br />JB