I have a Evinrude 1989 88 SPL, I have been researching the motor and carb part numbers and have found the only difference in the horse power of these V4 motors are the carburetor orifices (Jets). According to my research it appears I can convert the 1989 88 SPL, to a 115hp (1990 Model carb parts) by changing the high speed and intermediate carb jets. Can anyone confirm this before I buy the jets. Is it possible to convert the 90 hp to 115 this way.
I am pretty sure they have different exhaust ports/manifold (bubble back) and intake ports...Mostly speaking if you want a 115 sell your 88 and go buy a 115. These motors have a very specific balance and you have to really know your stuff to convert one that will run right. I have 2 115s a 25" shaft and a 20" shaft. the long shaft motor is a 1995 and the short shaft one is a 1997 OIS 60 degree motor...both are in excellent running condition and I would sell you one if you want to drive down here to Savannah. but you could probably find one there in the Atlanta area.
That is correct. The 115 blocks have different porting and a tuned exhaust manifold (bubble back) that helps with scavenging exhaust. Also, the carbs aren't just jetted differently, they're different carbs. The 115 has larger bore carburetors. Turning your 88SPL into a 115 would involve a great deal of machining and finding of parts. As noted above, if you want more horsepower, get a bigger motor...
I am in the middle of changing my 90 hp to a 115...while it is a looper not a crossflow, what i ahve found , PROBABLY applies to your motors as well.
first off just because you look up a part number and it says it fits both the 90 hp and the 115 hp...does NOT mean they are the same.. the heads interchange from a 115 and a 90./..BUT they are different..the depth of the combustion chamber is about .090" deeper on the 90 hp!!!
second, like someone said the BORES on the 90 and 115 carbs are way different...thus the volume of air going through is different...youd need the 115 carbs .
thirdly, while almost every rebuilder will tell you they sell a 90-115 hp block...they cant!! the ports in the sleeves are very different!
the 115 hp ports are larger and closer to the edge than the 90 hp ports. I took a foredom tool and ground the ports on my 90 hp to match those of my 115 hp( luckily i have a 115 already to measure from) as best i can tell all other parts are the same..
I would guess that it is at least as difficult to convert your 88 to a 115 as it was for me to convert my 90 to a 115...maybe even more...since i havent seen the exhaust housing on your motor...
on this picture the port on the right is the original shape for a 60 degree looper 90 hps, the port on the right is about the shape for the same style 115 hp!!
For what it's worth (not much probably), my mechanic told me he could turn my '81 90 into an honest 115 with a carb swap. This issue arose because he was troubleshooting my motor and found that some dopey previous owner had slapped 140 carbs on it. He said there would be extensive other modifications required to make it a 140. Despite my carbs being too large, he was able to get them jetted to the point where my motor runs well. He advised me to look for 115 carbs for it. I haven't though, because it runs awesome as-is and I figure why mess with it.
the problem really is that old wives tales have been passed around about making an X hp motor into an X+ hp motor by just switching carbs..or heads....and when the job is done and the motor runs good...the owner THINKS he has more hp, when in fact he probably cant tell the difference....
a guy would have to GPS his boat, then make the switch and then re gps the boat and verify the boat is actually going faster at the same rpm!!