is 2 cycle outboard more powerful than 4 stroke?

[ib18]

is 2 cycle outboard more powerful than 4 stroke? A guy posting craigslist ad for selling his Johnson 8 hp with the following statement: [FONT=Bitstream Vera Serif, Times New Roman, serif]This 2 cycle motor (Johnson 8 hp) puts out more power than the new 9.9hp four strokes. [/FONT]

[FONT=Bitstream Vera Serif, Times New Roman, serif]I don't think so, but want someone to confirm it and elaborate why?

Thanks[/FONT]

 

[F_R]

I've never compared the two motors in question, but isn't a horse(power) a horse(power? Sure, there are differences in how those horses are attached to the water, and the ease with which they slip through the water. Also, the RPM at which they develop the horses and the torque. So, maybe one will outrun the other. It's called a race.

 

[dingbat]

Horsepower is horsepower.

Even considering the rating system that allows a motor to be badged plus or minus 10% of the actual horsepower, the best you could get is 9.0 vs. 8.8. Close, but no cigar

 

[Bluestream]

He may be right...9.9 4 stokes are gutless

 

[Bluestream]

No Title

 

[Scott Danforth]

2-strokes have more power per a give cubic inch than most 4-strokes because you get power from every rotation of crank where a 4-stroke you get one power cycle per every 2 rotations of the crank.

is it more powerful - no. is the power in a better area of the RPM band to where you can use it more - most likely yes.

 

[jakedaawg]

Hp= rpm?torque/5250

Roughly.

A 2 stoke usually has a better power to weight ratio.

Some times a 4 stroke has better torque in certain situations but it isn't necessarily beneficial when considering weight and rpm limits

 

[jimmbo]

Well 2 strokes have better power to weight ratio in almost all cases. The 2 stroke has fewer moving parts. Each cylinder fires every revolution while a 4 stroke can only fire every second revolution. Does that mean a 2 stroke of a given displacement twice as powerful as a 4 stroke of the same displacement? No, a two stroke engine usually has lower compression than a 4 stroke, and again two engines using the same bore and stroke, a 2 stroke is using less of the power stroke to generate power as the opening of the exhaust and intake ports effectively ends the power stroke. Some energy is lost out the exhaust too.

As for the 2 stroke 8hp being more powerful than a 4 stroke 9.9... Well the 8hp will probably have more hole shot than the 9.9. Top speed will be hard to say which will be faster, if both are rated the same way,crank or prop, the 9.9 should be faster top end wise. but if the 8hp is prop rated and the 9.9hp is crank rated, there may be almost no difference

Myself I would take a two stroke any day of the week. With a two stroke I could go across the lake and be back before the 4 stroke even gets up on plane.

 

[TN-25]

There is a term they use, usually for heavy truck diesel engines, to describe the torque characteristics, called "torque-rise". It refers to the torque figure and how early it reaches peak torque.
A 2-stroke has the upper hand when it comes to off-idle torque & torque-rise, perfect for boat usage. As was mentioned by others it is a result of every downward stroke of the piston being a power stroke. Also the powerhead for a 2-stroke, at least the old ones, weighed about half as much as a 4-cycle powerhead.

 

[Silvertip]

I've looked at this comparison a lot over the years and until you get into the really high HP versions of each motor (which did not interest my curiosity) here are a few observations.
1) A two stroke will put an identical boat & load on plane quicker and at a lower rpm that the same HP 4 stroke.
2) The top speed of the boat will generally be slightly higher with the 2-stroke because the gearing in the 4-stroke is a slightly higher ratio (lower gear) to compensate for the lack of hole shot.
3) That same issues means the two stroke will have a lower engine rpm at the same boat speed.
4) The better 4-stroke fuel economy is something that also must be looked at carefully to make a reasonable comparison. Since boat SPEED at any given RPM will be faster with the 2-stroke, one must look at economy as a matter of BOAT SPEED vs ENGINE RPM - not just economy at the same RPM for both engines. The four stroke will win that comparison every time -- but remember, the 4-stroke is not pushing the boat as fast.
5) Tests have been done on noise and measurements between two stroke and four strokes show a lot closer numbers that the ear would dictate. The 4-stroke makes a very different sound than the two-stroke so ones ears just THINK the 4-stroke quieter when in reality it is a more "pleasing" sound. Compare it to nice easy to listening waltz music vs hard rock played at the same sound levels.
If one wants to make 2-stroke/4-stroke comparisons, Yamaha has a very comprehensive Performance Bulletin area on their web site where you can compare various boats, various engines, and performance charts.

 

[bspeth]

I'm not a waltz kind of guy baaaaaaaaaaaaaaaaaaaaaaaaaaa all day!

 

[ib18]

Thanks so much. I recently purchased a 2011 8 hp mercury 4 stroke kicker motor. Boy, that little baby vs my big Johnson 90 2 stroke. The little 8hp is so quiet and virtually no shake on my DIY outboard stand I built. My Johnson 90 was so loud, my entire street heard my loud motor roaming after I brought it home and started the engine for the very first time - LOL.

Thanks for the detail explanation. I think I will go with bigger HP every time regardless whether it is 2 or 4 stroke. Just need more power to push my wellcraft fiberglass boat.