Can I squeeze more HP out of my O/B?

[z86roc28]

Are there bolt on modifications available to make my 60 hp Mariner 3cyl 2 stroke run at about 70-80 hp? There are many things I can do to my 2 stroke arctic cat F7, was wondering if the same is true for outboards.

 

[Major Woods]

Re: Can I squeeze more HP out of my O/B?

On my other 2 stroke toys (jet ski, dirt bike) there are quite a few aftermarket items that can be bolted on to gain extra hp.
Exhaust pipe, head, high compression pistons, reeds, carbs, etc....
I have not heard of any of these item for outboards.

 

[z86roc28]

Re: Can I squeeze more HP out of my O/B?

I was thinking more on the lines of reeds, carbs, and exhaust work. I saw a prop that advertised 5-10% more hp because of enlarged exhaust ports. What other direction can I take? I want to have more air/fuel going in, more spark burning it up, and faster/larger exhaust ports. Basically, I want to take advantage of the existing design by maximizing the air/fuel/exhaust. Any ideas. I was thinking about a 6-71 Weiand supercharger, or maybe a set of edelbrock vortec heads, but I can't get any of the bolt holes to line up. Maybe I'll try an LS1 conversion.........haha

 

[Paul Moir]

Re: Can I squeeze more HP out of my O/B?

With a boat, there's way more to be had by working on setup than working on the engine. Is your rig efficient? Is the engine mounted as high as possible to reduce gearcase drag? Weight balance of the boat optimum? Can you get the boat to shed a few pounds? Engine operating at the right WOT RPMS? Boat bottom perfect?

As you probably know from your ski-doo experiences, engine hop-ups normally affect reliability. Especially on an engine that is expected to run full load WOT for a few hours at a time. Outboards and inboards are constrained by their restrictive, below-the-waterline exhausts. If you really want, you might construct an above-the-waterline exhaust, but it's use is restricted in many places and it's also pretty annoying to the driver.

5-10% improvement in HP by changing a propeller is unbelivable. But good, high tech propellers will allow you to raise your engine higher out of the water.

 

[z86roc28]

Re: Can I squeeze more HP out of my O/B?

The claim of a 5-10% hp increase is due to oversized exhast ports through the prop...I dont know if that is true. I have the prop matched to the hull, the bottom has no obstructions, basically, I want to mount a 60 horse motor on a boat that came with a 70 or 85 hp motor. But maybe it is not necessary, how well do you guys think 60hp would push a 1200lb hull?

 

[jtexas]

Re: Can I squeeze more HP out of my O/B?

Your engine might be built on the same block as a higher rated mariner engine. If so, compare the parts catalogues - could be as simple as carbs, manifold and cylinder head.

Is 1200lbs the "dry hull weight" per the manufacturer or an actual weight? What hull design, length, width, fiberglass or alum? It'll probably get you on plane, but don't expect 40mph, probably not 35 either. That's just a wildassguess.

 

[z86roc28]

Re: Can I squeeze more HP out of my O/B?

Good idea. I looked up a power head for the mariner, it is the same part for the 60-75 hp 3cyl. Where can I get a cylinder head and carbs etc for the 75 hp? Does anyone know for sure that something like this would work?

 

[jtexas]

Re: Can I squeeze more HP out of my O/B?

ishopmarine.com has online engine schematics and parts catalogues - I'd start there, compare part numbers for each part. With any luck they'll have common crank, pistons, other internals. After you price it out you may find it more economically feasible to sell yours and buy another - course then you miss out on all the fun - plus which you wouldn't know your new motor as intimately as this one.

And post the question in the merc/mariner section, in case somebody there knows something but doesn't see your question here.

Interesting project...keep us posted.

 

[Silvertip]

Re: Can I squeeze more HP out of my O/B?

The 60 HP Mariner 3 cyl is not the same as the 75. The 75 and 90 HP are the same block (1.3L). The 40, 50, 60 are the same block (966cc). But since we have no idea what year this is, its hard to tell. Check my response in your other post on the Mercury forum. If you have a 60 HP, the engine may be the equivalent of Merc's
Big Foot which is 2.3:1 gearcase. The 40 and 50 were typically 1.83:1 gearcases.

 

[cobra 3.0]

Re: Can I squeeze more HP out of my O/B?

By the time you are done, it will have been cheaper to sell what you have and just buy another higher hp engine.

 

[deejaycee_2000]

Re: Can I squeeze more HP out of my O/B?

Yeah you can modify that 60 to 80hp easy, it will cost you though ..... this can be done .... blueprint the motor, 1mm oversize boring on pistons, add a bullet or racing gearbox, welding and balancing of the crank, holes can be drilled or cut into the exhaust trunk, or shorten the exaust, modify the head, bigger fuel system and modified reed valves motor cowlings can also be altered to increase air flow, add an external water pick-up ..... stainless steel racing prop ..... we modified a 85hp yamaha to push out over 115hp ....