Re: Horsepower Upgrade
Nordy,<br /> Are you sure on not having to change the exhaust tube? It is obviously larger and a different shape on the 1989 15hp. I found that they didn't develop full WOT rpm, or power output with the 9.9 exhaust tuner left in place. What was your maximum rpm on your test wheel? What was the part number of the test wheel that you were using to verify the output? (OMC pt# 386537?)<br /><br />Without the exhaust tube changed, I couldn't get the first one to pull much over 5700 rpm on the test wheel. After I quit being lazy and changed the tube, it was pulling over 6000 rpm on the test wheel, and held within a close tolerance to a "true" 15hp in the on the water testing. 2 "conversion" engines were tested against the "real" 15hp engine. All engines were tested using the same boat, inductive tachometer, propeller and GPS unit on the same afternoon. The tests were performed in a relativly tight succession (as fast as we could swap the engines, test gear, and prop to the boat.<br />The tepmperature, wind velocity, and barometric pressure were stable. There was a 5kmh breeze, and testing was done with 2 upwind, and 2 downwind passes each, with the engines fully warmed to operating temperature prior to the runs. We used 3 seperate, but identical fuel tanks filled to the same weight, with the fuel coming from the same batch of premix. I was the operator for all 3 engines, and did not consume any food or beverages between runs, or go to the bathroom.<br /><br />We tried to make the testing as accurate as we could with what we had available to us at the time. Any readings that we obtained, although possibly not completely accurate, should be consistent throughout the engines we tested as we used the same equipment and tried to eliminate as many variables as we could from the results.<br /><br />I do not in any way deny that changing only the intake side of things did make a marked difference to the gross output of the engine, but did not bring it to the standard of a "real" 15hp engine, nor within and acceptable tolerance thereof.<br /><br />As our experience is only with the 1989 Canadian model year, short shaft, manual start engines, I can not vouch for others. <br /><br /><br />Cheers,<br /> Snow
<br /><br />What lead me to doing this was needing a few 15hp engines for inflatables for friends. In my area there seemed to be a shortage of good used 15hp engines, but a supply of 9.9hp ones. <br /><br />What I have found is that the torque and hole shot of the 9.9 is almost identical. Where the 15hp comes into it's own is at the top end as it runs about 1000 rpm higher at WOT, than the 9.9. The 9.9 has a far better manner at idle than the 15hp does. My thoughts are if you do not need the absolute top end of the 15hp, or use it for trolling any amount is to stick with the 9.9. If you have to buy the parts new from the dealer, the conversion is not cost effective to do, it is cheaper and far less hassle to sell your 9.9hp and find a good used 15hp. Or if it is "looking" like a 9.9hp that you desire, find a used 9.9 cowl cover of the right year series to stick on a 15hp motor. If it looks original, I doubt anyone would actually check your model # on the water. (please don't ask why I say this 
