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dtoole

Regular Contributor
I have heard conflicting answers to this question. I want to learn what modifications to make to 2 stroke outboards for performance gains. I used to race cars at the drag strip. was always trying new things to get more out of a motor. My "local marine machinist" ,a dirt track racer himself, told me that compression gains are about the only way to increase hp. he said however that the motors wont last and cautioned me against it. I just politely took his advice for what it was worth. I simply dont know anyone that has played with outboards. i am looking to build one. any input would be appreciated.
 
You can't lump all two-strokes together for that question. Some are already set up for maximum output with any level of reliability and durability. However, some are deliberately de-tuned when built to fill in gaps in the horsepower offerings. Having said that, you obviously are focusing on race-type situations where every horse counts. I'm sure you know that is a mighty iffy thing. You may make it better and you may make it worse. Go ahead and play with it if you have the time and money and can afford to lose a motor if it doesn't work out.
 
Actually, there is a quite a bit that can be done to a two stroke to get HP out of it. I've currently got a 1983 140 OMC, that is probably making 160 to 170 hp. It's been ported, all rotating components balanced, light weight pistons, high compression (160 psi) heads, larger carbs, aftermarket reeds, light weight flywheel, etc. Depending on the max timing advanced used, this can be a lake motor (like mine is), and run on premium fuel, or set up for racing and run 100 octane Aviation fuel for even more HP, but a shorter life.
 
The reeds are aftermarket, the carbs are from a 150 hp (they are a bigger bore than stock 140 carbs), the flywheel is from a 70's cross flow motor. The high comp heads are also from a 70's 140 hp, without the coil mounts found on the later motors. So I had to run a 70's type coil holder and ignition on the motor.
 
wow....what kind of duck was that?

I have three 1960's vintage 40 hp OMC's that I'd be willing to ruin/experiment with....any suggestions where to start? Or do you think they are too pokey to bother with?
 
It's a fast duck!!! And except for the water telltales (4), its hard to tell it from a stock mid 70's V-4, unless you know where to look. A V-4 that will out run V-6's, and with a 1980 115 cowl on it just to shake up the guys that think it's a run of the mill boat/motor. :rolleyes: I don't hold much hope for the 1960's 40 hp motors. They really don't have the potential that the newer motors have. You might be able to get a few more ponies out of them, but the gain won't be worth the effort.
 
obviously, i am on a omc forum, but opinions about the best/most economical hot rod outboard would be interesting.
 
From the little I know :rolleyes: I have to say that Mercs are gonna be the fastest hot rods. BUT, they are also gonna be the most expensive.. OMC's, although they don't rev out as high as most Mercs, seem to have more torque. AND, they are cheaper generally, and so are parts. BUT, Mercs seem to have more performance parts available. So, call it even, but you'll see more black motors on fast boats. Me, I'll stick with my OMC's, if for no other reason than I can go into any OMC/BRP dealer, and parts are either in stock, or can be ordered, and will show up the next week!!
 
What motor do you want to play with? Knowing that may help to get some specific answers to help in your quest. This can be fun and very rewarding. It'd also help to know what boat you're going to use. Some hull designs respond better to torque increases than others.
 
Suggestions for a hotrod project OMC model would be really interesting. Once a model is determined as desirable then the search could begin. Motor first. Boat later. 2 cylinder, 3 cylinder, V4, whatever. As long as it is available in the second hand market, plentiful and affordable then we are off to a good start.
 
I can only talk about the v-4's, that's the limits of my experience. Lots of them out there, and cheap. Get one with a bad cyl, since it's going to be bored anyways (mine is 0.030 oversize). I have heard that the 3 cyl 65's are also good motors to work on, and you can produce some good results with them.
 
Get a 3 cylinder 75 HP Evinrude or Johnson.-----From the mid 80's , there are lots of cheap parts around and even performance lower units in short shaft.
 
i was thinking 200 + hp my wife tells me that i have a death wish. i say just a need for speed. what year did they start making these high hp motors?
 
dtoole said:
i was thinking 200 + hp my wife tells me that i have a death wish. i say just a need for speed. what year did they start making these high hp motors?
Click to expand...
LOL... I'm looking for a 225 to replace my 140!! Sounds like we have the same need!!:cool:
 
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