25hp 2 stroke 3 cylinder Johnson

[Tim Kurcz]

Tim,

Got it. Im at 6200 WOT right now with mine GPS'ing at 37.5 - 38.0 MPH. Thats with a 14P SS powertech prop. I'm not quite to my magical mark of 40 mph, getting close.

You're pretty close. Props, bottoms, and CG are everything. Have you had custom prop work done - thinning/cupping/shaping? Jacked the motor higher on the transom? Moved ballast aft & re-trimmed the engine? Cleaned, smoothed, waxed the bottom? You might get more than 40.....

Tim

[speedfreak]

Yeah, I'm going to get after it again after hunting season is over. Should be able to get a couple mph with a few more tweaks.

[champ20B]

http://www.boatracingfacts.com/forum...t=7707&page=17

Hey Speedfreak, In case you hadn't seen this before. I built this 35HP OMC triple for my son's 11' runabout. It runs 55MPH at 5750 RPM on the A15 racing gearcase. If you need to run a shifter, contact Ron Hill for a racing prop.

Tim

BTW: You'll want to get 35HP carbs and open up the airbox.

Hi, I think I seen this motor or one like it on the (Quincy Looper Website). It looks great!! My brother and I have a 35 triple OMC, and we love it. It's a great motor.
My question though is about the speed to horse-power. I thought that a set up like this would be super fast, "at least like a really good Yamato 302" at 65mph or so. What I mean is that an old Mark 20H or Evinrude-15/A will run in the low to mid 50s easy. Is it because the little stock 15-20 cubic inch motors are actually making in excess of 30 actual horsepower? This is an honest question. I never seen any actual horse-power ratings on many of these little racing engines except for the Yamato 80. I happen to own a Y-80, a 1956 Champion Hotrod-20, and a super-10 mercury. Thanks.

[JohnsonM50]

Hi, I think I seen this motor or one like it on the (Quincy Looper Website). It looks great!! My brother and I have a 35 triple OMC, and we love it. It's a great motor.
My question though is about the speed to horse-power. I thought that a set up like this would be super fast, "at least like a really good Yamato 302" at 65mph or so. What I mean is that an old Mark 20H or Evinrude-15/A will run in the low to mid 50s easy. Is it because the little stock 15-20 cubic inch motors are actually making in excess of 30 actual horsepower? This is an honest question. I never seen any actual horse-power ratings on many of these little racing engines except for the Yamato 80. I happen to own a Y-80, a 1956 Champion Hotrod-20, and a super-10 mercury. Thanks.

20H's 15A's, they can run that fast but the catch is it has to be an aired out race hull, efficiency is the reason. The gearcase is geared for more prop rpm & to compensate for the need for power the prop size [dia mostly] is reduced on race gearcases. This would not work well on a normal 'wet' hull. The 35x3 has a huge gearcase & itelf a limiting factor. Getting it all right at the same time should put up 40 or so & if you got into one as full a racer with a tower & gearcase upper 60s or more on a hydro is likely possible.

[champ20B]

20H's 15A's, they can run that fast but the catch is it has to be an aired out race hull, efficiency is the reason. The gearcase is geared for more prop rpm & to compensate for the need for power the prop size [dia mostly] is reduced on race gearcases. This would not work well on a normal 'wet' hull. The 35x3 has a huge gearcase & itelf a limiting factor. Getting it all right at the same time should put up 40 or so & if you got into one as full a racer with a tower & gearcase upper 60s or more on a hydro is likely possible.

Yes, your right about that. But he built this using a 35 triple powerhead on a "class-A OMC" racing midsection and a racing gearcase thereof. As far as I know, Tim Kurkst is a highly experienced racer who put this combo together for an 11' runabout. All I can assume is that the hull would be about equivalent to a "class-C" racing hull. I thought about that motor when I saw it and estimated that it should be at least a 65 mph runner, although not a legal competition engine. This clearly indicates that the traditional 50-55 mph racing motors should be doing at least 30 HP. I know that the Y-80 is rated at 30HP, but it can do better than 55 on a runabout as just a properly set up runner, not engaging in continuous turns and race conditions.

[champ20B]

Yes, your right about that. But he built this using a 35 triple powerhead on a "class-A OMC" racing midsection and a racing gearcase thereof. As far as I know, Tim Kurkst is a highly experienced racer who put this combo together for an 11' runabout. All I can assume is that the hull would be about equivalent to a "class-C" racing hull. I thought about that motor when I saw it and estimated that it should be at least a 65 mph runner, although not a legal competition engine. This clearly indicates that the traditional 50-55 mph racing motors should be doing at least 30 HP. I know that the Y-80 is rated at 30HP, but it can do better than 55 on a runabout as just a properly set up runner, not engaging in continuous turns and race conditions.

I spelled his name as Kurkst. I apologize about that. It is Tim Kurcz.

[JohnsonM50]

I think what Tim put together has potential to go faster, a matter of decision to go there but that of course, his call. The OMC 15 is a motor of specific parts to be legal & might be slightly enhanced but totally not 30 or even 20HP its use of a hull & prop set up to do those speeds make it happen, more RPM than HP.The Mercs on the other hand I wouldn't venture a guess.

[champ20B]

I think what Tim put together has potential to go faster, a matter of decision to go there but that of course, his call. The OMC 15 is a motor of specific parts to be legal & might be slightly enhanced but totally not 30 or even 20HP its use of a hull & prop set up to do those speeds make it happen, more RPM than HP.The Mercs on the other hand I wouldn't venture a guess.

Yes. That makes sense to me. I suppose it is just rpm and not really a hp issue depending on other set up factors. A bigger or higher pitch prop would probably pick it right up. The thing is, I am strongly considering a build of this type using the 25 triple OMC powerhead. It is right at 30 cubic inches, which could be an excellent "C" mod or superstocker if it could be properly introduced and accepted as a probationary type set up, using the "A" mid and lower or some other combo thereof. This could be something of an excellent idea, as a good option of modern engine choices, in certain venues of outboard racing. We could have another Tohatsu racer "metaphorically speaking".