Re: Honda 35 - 45 or 40 - 50 upgrading
Spidybot was referring to upgrading an older 35 to 45, or a newer 40 to 50.<br /><br />The 35/45's ('91 - '94)
are different than the 40/50's of current. Different carburetion, ignition, larger valves (on 40/50's), and different camshafts.<br /><br />But....there is no major difference in the older 35 vs. 45 model. And there is no major difference in the newer 40 vs. 50 model. Over time, the 40/50 simply replaced the 35/45 with a better and more efficient motor. There would be a major difference going from the older 35 to the newer 50.<br /><br />In Honda's line-up, similar displacement engines produces several different hp ratings because some hull certifications, and some consumers, require
lower ratings than what that engine is capable of. Usually these ratings are
higher than the next engine design down can produce. It would be costly and timely to produce a specific engine design for each hp class.<br /><br />Thus, in the marine wold this is called "detuning" or "derating". It is a method used by all manufacturers in order to offer a wide range of hp ratings. It generally does not include using different internal parts as J.B Cornwell states. It generally means an rpm reduction by detuning carburetors, using a throttle cam limiter, or retarding timing, etc. Nothing major. For the newer electronic fuel injected outboards this may mean a simple reprogram of the PCM. For older carbureted outboards it may mean a simple jetting change.<br /><br />Re-rating, or retuning is certainly possible without internal engine modifications (as long as the powerheads are the same as the 35/45 or 40/50) You will only know what you need to do by looking at the parts book. It could be as simple as a $10 throttle cam. <br /><br />As an example there is no way possible to upgrade the Honda 30 to a 35. The 30 is at the top of its hp rating for a Honda 499cc. It's simply not capable of making more power. But the 25 is also the same 499cc engine, so it could probably be upgraded capable of making 30 hp. <br /><br />The only way to get a 35 Honda would be to detune a 40 or 50 (factory "detuning" parts are available from Honda). Same if you wanted a 45. You would have to detune the 50. You can't go up unless you're in the same engine displacement category, but you can go down. IMO, this is done with a throttle limiter. Again, limiting the RPM will automatically limit hp.<br /><br />J.B Cornwell said,
"The throttle cam change you use is a limiter, not a detuner."<br /><br />Well, Honda and Yamaha call them "de-tuners" (see link below). As I said,
"The de-tuned throttle cam limits the engine's ability to run WOT." 
Here (one of the very few places in the country that specifies HP on bodies of water) enforcement, guides, and marine outfitters have called it "de-tuning" for years. You will find the terms "de-tuning" and "de-rated" (not limited) used by all the manufacturers.<br /><br />
"To change the peak hp, which, as you say, would occur at different rpm, one can change valve lift and timing, ignition timing, etc., as I mentioned above."<br /><br />J.B., I assumed when you previously said
"camshaft profile" and
"compression ratio" that you meant modifying internal parts such as camshaft, head, piston, etc. I just can't see how you can change the camshaft profile or the compression ratio without internal engine design changes. And I can't see why the manufacturers would go to this extent to detune a 50 to a 40, or a 45 to a 35. It's much easier and less costly to limit rpm or change the carburetors.<br /><br />
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http://www.advancedmower.com/honda_outboard_conversion_kits.htm
