Overrated Horsepower?

[dfrants]

I have read that most outboards produced in the 70's and early 80's were sold with higher horsepower numbers than they actually produced( i.e. the Merc 50 was actually 45hp, the 80 only 75hp), was this true with the Merc V6's also? I've found a good running 1980 Merc 175 and was curious if it actually produces 175hp?

 

[racerone]

In the early / mid 80's the motor rating was changed from power at the crankshaft to power at the prop.---So yes , an older motor had a higher number on the decals.

 

[roscoe]

I doubt that many 45 year old outboards are going to produce the hp on the decal.

Also, the NMMA hp rating specifications allow a 10% +/- deviation from the rated power.

So even a new modern engine rated at 175 hp may only be
producing 158 hp.

Your 1980 block rated motor could have been rated at 165 at the prop, minus a possible 16 for rating error = 154..

Then subtract ??? hp for any wear and tear and tuning issues.

 

[cyclops222]

Does it start every time in 1 second or less ?
Does it run smoothly at all speeds ?
You do not need to post any what ifs.

 

[retroroy]

Does it really matter what number they put on any motor? We have no way to verify how much power its really making.
Its not as if we can take our boats or outboards down to some dyno and have them tested.
At best all we can go on is the displacement, number and size of the carburetors and compression ratio and make an educated guess, that is if there really ever was a baseline.
If you look across the board at all the brands, motor displacement and arrangement vary greatly but performance generally does not.
One may be a little faster or little quicker out of the hole shot but rarely does any motor with the same rating completely blow away another witht he same rating.

Around 1984 they changed from power head to prop rated HP advertising but from what I've seen that simply subtracted the roughly 15% power loss at the gear box from the decal on the side.

I would think you loose more power over time as a motor wears, as the fuel pump looses efficiency or as the carb adjustment falls out of optimum range over time. This happens with any engine, some faster than others.
Most motors are at their optimum power at the point of 'break in'. Once the rings have seated and the engine is in proper, optimum state of tune.
It goes downhill from there.

Unlike automobiles, an outboard has even more variables to consider, prop blade flex, pitch, and cup all affect the effective prop hp. The change can be slight but it adds up.

The reality is that the number on the side of a motor is a suggestion at best, rated to a standard that in many ways is partly irrelevant to most owners other than being a baseline or indicator of 'about' what to expect.

We would certainly expect that if we removed a 90hp outboard in favor of one marked 115 that we would go faster and have more power. Regardless of brand, or type of motor. However the reality is do we really know what 90 or 115 hp really is in the real world.
It goes back to the fact that any engine is simply an air pump and all we can go on is seat of pants feel and actual performance speeds.
Over the years I find that hull design, weight, and weight distribution has as much to do with how well any outboard performs as does the number on the side of the cover.
.

 

[racerone]

Many marinas / boat shops now have a dynamometer to accurately check power output.-----Marketing / production management also has a lot to do with the decals put on motors.----Some actually produce more power than stated on the decals.----Evinrude 100 XP was really a 115 marketed as a " powerful / extra performance " motor with 100 on the decals.