make a 9.9 into a 15

[lynch_00]

I have a 84 evinrude 9.9 that I would like to get more power from. I heard that you can just change the carb to a 15hp carb. Is this true? and if it is, where can I get the carb and how much? Any other power tricks?<br /><br />Thanks

 

[JB]

Re: make a 9.9 into a 15

Howdy, Crappiebasser.<br /><br />Changing the carb might get you a little more power, but not enough to justify the cost. You probably wouldn't notice the differencce without a GPS or a stopwatch.<br /><br />To get it to 15hp would require more parts changing and modification and would definitely cost more than a used 15.<br /><br />What makes boats go is torque and rpm. Torque is mostly a function of displacement and compression ratio, plus ignition and port timing. <br /><br />The 9.9 and 15 have the same displacement. Getting more REAL hp requires the 15 to have more air/fuel mix (bigger carb or improved exhaust scavenging), more compression, different timing, rating it at a higher rpm, or, most likely some of all of the above.<br /><br />While the old saying that there is no substitute for cubic inches is not 100% true, it is danged close.<br /><br />Getting more power with the same displacement is not worth the bux unless you are racing in a displacement class and have both bux and engines to spare.<br /><br />Red sky at night. . .<br />JB

 

[Waco]

Re: make a 9.9 into a 15

I have a 9.9 johnson 1974 model. the only difference in it and a 15 in 1974 was the carb. (bigger throat), but then in the early eighties (i believe) when they started measuring PROP HP, they also changed exhaust, and reeds. If I were you, I would compare parts breakdown between the two. By the way, I found a 15hp carb. on EbaY for 20bux. already rebuilt.