1986 90 HP merc

[wierdkid]

can anyone send me or post the spec sheet or at least the gear ratio and WOT RPMs for a 1986 90hp merc (inline-6).

[sosmerc]

Gear ratio is 2:1 and max rpm is 5000. The 115 version of that powerhead uses the same gear ration but max rpm is 5500.

[wierdkid]

big thanx fo the info

[wierdkid]

does anybody know how to and what parts i might need to raise the rev limiter to 6000 or beyond (just as long as the engine can handle it for extended runs with out upping the oil in the fuel)

[wierdkid]

heck even 5500 would be fine

[sosmerc]

Merc did not use any kind of rev-limiter on the inline six. You are simply limited by amount of air and fuel that can be pumped through the engine.....and that is dictated by such factors as size of carb venturi, flow thru reed blocks, porting, exhaust flow..etc.

[wierdkid]

what thingscan i do or parts can i use to unleash a few horses while keeping the engine reliable that would be relatively inexpensive (diagrams would be helpful, the carbs look entirely foreign to me and i dont know too much about the layout of the i-6s)

[Jeff_S]

I have a 1986 90 horse inline 6 sitting in my garage that has very few hours on it and runs absolutely perfect. The reason I took it off my boat was that it wasn't enough motor for my boat and there are very few things that can be done to this particular motor to hop it up. The reeds are mounted in such a way that you have to remove the engine to get to them and I understand that even reeds will not help it much. The one thing that makes this motor different form the 115 is the porting of the block. There is not much that is available for this motor aftermarket to give it any gains. If you step up to the 115 or the 150, that is a different story, but this motor is destined to be a dog. It is very reliable and bullet proof if you keep the carbon out, but other than that, you will be happier and it will be cheaper in the long run to sell it and buy a V6 if speed is what you want. Sorry for the bad news, but it was given to me that way and I was grateful that I didn't tear into it and then find out later that any mods would be for practically nothing without severly modifying the block. You can search this board and you may find some previous posts about my questions or others.