Horsepower Ratings changed when and why

[Boynsea]

Hello all, I have a 1974 IL6 1150. It is completely rebuilt and runs awesome. I have it mounted on my 1989 Spectrum 1700 dual console open bow aluminum outfitted for fishing. I was told that my 115 is actually like a 100, which would explain why I only top out at 32 MPH on GPS with a full load (19P or 17P seems to make no difference). I am curious about when the horsepower ratings were changed on these and why they did it. From what I can gather, they used to be rated at the crank, and are now rated at the prop. Can anyone enlighten me?

 

[oldseaox]

Re: Horsepower Ratings changed when and why

Yes they did. Now, try to not let MPH and HP be your judge of performance. The numbers that mean the most to recreational boaters should be RPM at wide open throttle adjusted for load. If you can be within 10% of factory rated RPM at WOT then you are above average and if you can be within 2% then come tune my Merc. The only time MPH comes into play is navigation and now the GPS does that.
Sounds like you have a good running rig, enjoy.

 

[jimg984]

Re: Horsepower Ratings changed when and why

1983/84

 

[Thumpbass]

Re: Horsepower Ratings changed when and why

my understanding as to "why" is because japanese motors were being rated at the prop (while american at the powerhead)...therefore imports of equal HP rating were out-performing the domestics...so domestics changed to rating at the prop as well. just what i read, could be wrong

 

[Thumpbass]

Re: Horsepower Ratings changed when and why

Yes they did. Now, try to not let MPH and HP be your judge of performance. The numbers that mean the most to recreational boaters should be RPM at wide open throttle adjusted for load. If you can be within 10% of factory rated RPM at WOT then you are above average and if you can be within 2% then come tune my Merc. The only time MPH comes into play is navigation and now the GPS does that.
Sounds like you have a good running rig, enjoy.

if you fish bass tournaments in the south, MPH is very important haha

 

[Boynsea]

Re: Horsepower Ratings changed when and why

Yes they did. Now, try to not let MPH and HP be your judge of performance. The numbers that mean the most to recreational boaters should be RPM at wide open throttle adjusted for load. If you can be within 10% of factory rated RPM at WOT then you are above average and if you can be within 2% then come tune my Merc. The only time MPH comes into play is navigation and now the GPS does that.
Sounds like you have a good running rig, enjoy.

OK, so do you have any idea what I need to install a tach onto this motor? I know I need one, but I've looked at many of them and am quite frankly not sure which one to get. I saw a new vintage one on ebay and wish now I had bought it and taken the chance...

 

[oldseaox]

Re: Horsepower Ratings changed when and why

I apologize to the bass tourny people but I am a salt water fisherman and don't have a speedometer on my boat.
My sugestion is to buy a new tach as they come with instructions for different outboards. Most outboard tachs can be connected to the rectifier which is in the charging circuit and will also have adjustments or settings for the paticular outboard.
The tach is also somewhat of a telltail for the rectifier, last time my rectifier went bad the tach became erratic and then stopped working.