Re: mercury upgrades
Here we go again. The 115 is a 116 CI (1741 CC) engine. The 75 and 90 are 97 CI (1596 CC) blocks. You therefore cannot convert either a 75 or a 90 to a 115. To determine what needs to change, to make a 90 out of a 75, go to the Mercury Marine web site and click on Parts Express. Enter your model number and a model number for the engine you want to upgrade to. Then all you have to do is compare every part number for both engines. Those numbers that are different are different parts. Just because an engine has the same displacement (CC) does not mean everything inside that engine is the same. All it means is the bore and stroke are the same. Heads, cams, exhaust, intake, EFI components such as injectors and the ECM are just a few. Gear ratio may be another. On some small engines there were carburetor restrictor plates that could be removed, and in some cases a larger carb would get you 5 HP or so. It is very easy for the manufacturer to create these variations. It is very expensive to make the changes after the fact. The parts cost will make it very cost prohibitive in most cases. Price four new injectors or an ECM and you will understand. You too will come to the conclusion that you sould have bought a 90.
