May the real 25 horse stand up!

[bigtwin]

Back in 98 I became the proud owner of a new 25 h.p. Evinrude 2 cyl. I was looking at the 3 cyl. at the time but decided it was'nt worth the extra $$ and the wait. Even though the 2 cyl. has served me well I always thought the 3 cyl. was more refined. I am now looking at the test wheel specs. for both motors. 2 cyl 4800 rpm, 3 cyl. 4200 rpm, they both use the same test wheel #434505, they also use the same lower unit and gear case ratio 2.15:1, 600 rpm differance WOW!!! Can someone tell me how OMC rated horse power, and is this kind of discripancy normal for all makes?

 

[DJ]

Re: May the real 25 horse stand up!

There is another variable-torque. I suspect the 3-cyl. has more.<br /><br />The 2-cyl. 25 is an older design and proven to be just about bulletproof. The 3-cyl. is proving to be much the same.

 

[Texasmark]

Re: May the real 25 horse stand up!

Hey Fast Twin<br /><br />Where'd you get your sign on handle?<br /><br />Wasn't the Fast Twin the 18 hp engine OMC built in the '50's......Had a '58 18 hp Rude "Fastwin" as I recall. Gave $400 for it new. Kept it in my room when I was a kid. Mother thought I was nuts but let me do it anyway. Water skied behind it....not fast, but skied. <br /><br />I remember it's big brother, the 35 hp twin was called the "Bigtwin". My (now) wife's dad had one of those. But that's been a long time ago. May have forgotten something.<br /><br />Mark

 

[bigtwin]

Re: May the real 25 horse stand up!

Hey texasmark<br />Back when I was 14, I was able to save my paper route money to buy an old fiberglass boat with a 18 hp "Fastwin" from the Wisconson DNR and spent many summers fishing the back waters of the <br />mississippi, I now look back at these times as the best in my life. I later sold it to my uncle and I think he still has it. It was a great motor.<br /><br />I Thought horse power was a formula of work over time. (torque X rpm / constant) So would'nt torque <br />be reflected in the h.p. rating?

 

[steelespike]

Re: May the real 25 horse stand up!

I'm sure no specs expert but it would seem to me that any motor on a test wheel should approach its max WOT rpm.I wonder if you have a miss print or possibly some qualifying info that is missing.

 

[JB]

Re: May the real 25 horse stand up!

All those specs mean, FT, is that the triple develops its peak torque 600 rpm lower than the twin. That is to be expected with more cubic inches. They say nothing about rated or actual HP.

 

[cobra 3.0]

Re: May the real 25 horse stand up!

In this instance, does this mean the three cylinder is incapable of reliably reving as fast as the two cylinder? ...or is it that the engine in 3 cylinder is detuned and capable of reving higher and producing even more horsepower if a larger carb was installed?

 

[steelespike]

Re: May the real 25 horse stand up!

All it means is that the 3 cylinder developes its max torque at 600 rpm lower than the 2 cylinder.Thus its low end power is stronger than the 2 cylinder.Hole shot may be better all things being equal.<br /> The max torque for both engines may be close it just peeks at a different rpm.<br /> Overall performance would be similar.My guess is WOT rpm is roughly the same with max speed in the same ball park.It is possible higher horsepower motors are based on the same 3 cylinder block.

 

[JB]

Re: May the real 25 horse stand up!

There are a lot of differences.<br /><br />The 25 twin is a crossflow, 521cc engine that peaks HP at 5000rpm. Operating range is 4500-5500rpm. It is similar to the 30HP twin, which peaks HP at 5500rpm. and has an operating range of 5200-5800rpm. It has manual tilt and uses mixed fuel.<br /><br />The 25 triple is a loop charged, oil injected, 500cc engine that peaks HP at 5500rpm. Operating range is 5200-5800rpm. PT&T is standard on the long shaft electric start, remote steering model. It is similar to the 35HP triple, which is 565cc and has the same peak HP rpm and operating range.<br /><br />In summary: The triple peaks torque at lower rpm, revs higher and uses significantly less fuel than the twin. It also costs more but is modern technology and has oil injection and PT&T.<br /><br />The twin is a basic, low cost model without oil injection or PT&T.

 

[Texasmark]

Re: May the real 25 horse stand up!

Hey Fast twin,<br /><br />Thanks for the info. Like I kept mine '68 Fastwin)in my bedroom on a stand.....tank outside. Had no other place to put it and I didn't want it to get dirty. Ha.<br /><br />On your equation, the problem with it is not the equation, rather the fact that the torque falls off after the peak (in some engines, real fast) as the guys mentioned. So more rpm's don't necessarily mean more hp. That's one reason why people talk about keeping your rpm's where they belong at WOT. <br /><br />I think JB or Dhadley (spelling) have discussed it on different occasions......like I remember one thread where the comment went like......."......having long passed the peak of the torque curve......".<br /><br />Mark

 

[rodbolt]

Re: May the real 25 horse stand up!

texasmark<br /> an easy way to think of it is the crank throws are levers acting on a fulcrum(crank mains) to impart a rotation. the longer he offset of the crank throw(stroke) the more power the lever can impart. but general piston speed and bearing speeds increse as well. now the two cyl has a power impulse on the lever at 180* intravals and the 3cyl at 120*intravals, the load(propeller) is constantly applied. which engine configuration will keep the prop moving against the load at a more constant rate?<br /> the stroke and bore sizes are roughly comparable but the induction systems are a bit different.<br /> its odd and its funny and the extracyl's add weight and some frictional losses but the extra impuls on the lever is worth it sometimes. same as comparing a 292 inline six with a 283. both have about the same CID which makes more power and goes faster?<br />its also why V-10and V12 were popular and 18+ cyl radial engines could make such staggaring amounts of power.

 

[bigtwin]

Re: May the real 25 horse stand up!

The test wheel is nothing more then a dynomometer, it applies a constant load to the engine at the prop shaft,<br />a pass/fail spec. is given by the mnfg. The test wheel is blind to how many cyls. are turning it, where the peak tourque value is in the powerband, or the displacement of the engine. Given the gear ratios of both engines are the same, wich one is the true 25hp engine, the 2cyl. spinning 4800 rpm, or the 3cyl. spinning the same test wheel at 4200 rpm. Either way my buyers remorse is now gone.