Discussion with friends about buying a new outboard when the question came up.

 

Mercury list the following 

60 hp 

In-line 4 cyl

CDI 60.8

RPM 55-6000

 

50 hp

In-line 4 cyl

CDI 60.8

RPM 55-6000

 

40 hp

In-line 4 cyl

CDI 60.8

RPM 55-6000

 

The question is what is the actual difference?

 

Curious to hear from @Way2slow ?

Supposedly the Yamaha SHO 200 thru 300 HP outboards are all actually the same motor mechanically - But with different tuning to achieve the desired HP.  Assuming it's the same with the 115 thru 175 HP SHO models too.  

 

Might be something like that going on with the Mercury's you're talking about?  Would be my guess anyway.  

I know for the 2 strokes mercury would use the same block and the motors were tuned different. Guys on another site would talk about buying a 75hp and have the CPU flashed to a 115hp to save a few grand in motor cost. I imagine its something similar. I also imagine it would void warranty. 

Not sure about the 4 cylinder engines, usually different ignition, injectors, and exhaust horns using the same cu in power head.

Tom

Outboards of similar size are often built on the same platform but de-tuned to make certain horsepowers. Go with the 60

Many times it's as others have said, it just the programing of the ECU.  However, sometimes it's a difference in porting and intakes used.  To check that, if you can come up with a factory parts breakdown, you can compare part numbers on the bock, intake and exhaust tuner.  Those are the main things that affect the horse power. 

For instance, back in their day, OMC's 3.0 V6 was a 200hp with 1 3/8" carbs and a 225 with 1 7/16" carbs.  The 250/225HO was the 225 with larger exhaust ports.

   Mercury and BRP only changed the ECU programming for the 200, 225 and 250, so Mercury may do the same thing on the one you are interested in, but can't for a fact that's all they did.      

One thing though, a lot of time you don't really notice a big difference in the motors on the hole shot, but there is a difference in top speed.  The cubic inches is what mostly gets it up on plane, the HP makes it go faster.

Yep, look on Merc's parts site.  I would assume there is a restrictor plate on the lower models that isn't on the 60, for example.  But most replacement parts would be the same for all.  I've looked at this for my Yamaha, and I think the only difference between mine (50) and a 60 is the ECM and that restrictor plate.