Fuel

[Boatboy88]

Hey everyone,
I have a stock 1974 Evinrude 15 hp fishing engine and was wondering how much more power could I make if I used alcohol as fuel instead of gasoline. Also with a motor like this making more power than it is intended, is it more prone to blowing up? I want to see how much faster I can get my engine to go.
Thanks a bunch,
Dan

[Tomtall]

wouldn't do it

That year of 15 had smaller wrist pins bearings that were pron to fail when run hard. Also had poor exhaust system, point ignition system and a larger combustion chamber head. All not suited for converting to methanol fuel. Don't waste your time. Look for a 1992 OMC 15 hp. All the work has been done to make that engine run much better than your model year. Megaphone tuned exhaust, tighter chamber head and CD ignition. I just coverted a 1974 over for a friend of mine at work to the 1992 spec's less the wrist pin bearings which I said I would not cover if she blows. I have attached some pictures of the coversion so you can see the differences between the two motors. The first pic is stock 1974 exhaust mid section. Second pic is 1992 restricted mid section suited for use with the exhaust megaphone exhaust. Cylinder head is self explanitory as it has a tighter squench band that promotes better burn and h.p.. The updated cylinder head does require a cut out in the engine cover to make it fit. This engine runs extremely well now with these updates done to it. I would recommend a 25/1 oil mix to help the wrist pin bearings live. Running a engine on methanol for pleasure use is a pain as you have to have a way to run the engine on a gas/oil mix after using it every time or the engine will rust all to heck while sitting around.

[Tomtall]

One more note

You will also gain approximently 300 more RPM on this set up if you run a dry exhaust tunner. This can be achived by using JB weld and blocking the water flow so it goes out the short water tube on the 1992 megahone set up and dumps it out the back side of the mid section as our racing 15 OMC's do. You will want to drill a very small piss hole in your water inlet tube so it spays water on your rubber motor mounts or they will burn out from being run without cooling in the mid section.

Good Luck !

[sam]

Without the mechanical modifications the fuel switch alone will only give a minimal power increase when the carb jetting is perfect. (I don't recall the general rule of thumb, but its something like 5%.)

You did not indicate you understand there will be a major change in jetting to do the switch ... you can't just dump out your gas and fill the tank with alcohol. The fuel density is dramatically different between gas and alcohols.

[David_L6]

Hey everyone,
I have a stock 1974 Evinrude 15 hp fishing engine and was wondering how much more power could I make if I used alcohol as fuel instead of gasoline. Also with a motor like this making more power than it is intended, is it more prone to blowing up? I want to see how much faster I can get my engine to go.
Thanks a bunch,
Dan

I wouldn't even consider running alky in that motor. In fact, knowing what I know now, I wouldn't run methanol in any motor that wasn't designed to run it. Need to make too many changes to a motor designed to run on gasoline to get the advantages from running alky.