2 or 3 cylinders, does it really matter?

[waterinthefuel]

I've heard that 3 gives more torque, but that 2 might give better fuel economy.<br /><br />This, of course, is regarding 2 engines of the same horsepower.<br /><br />Any comments or ideas?

 

[phatmanmike]

Re: 2 or 3 cylinders, does it really matter?

well looks like you figured this one out , eh?! more cylinders, more torque, thats a given. the les cylinders, the les fuel being burned...um

 

[rickdb1boat]

Re: 2 or 3 cylinders, does it really matter?

Not mention MUCH smoother running at idle. 3 cylinder loopers are know for their reliability and power, too.

 

[waterinthefuel]

Re: 2 or 3 cylinders, does it really matter?

That's something I don't understand. I went to check out a 3 cylinder Tohatsu 40 and he was saying that the older 2 cylinder 40's were weak. I don't understand, if both have 40hp at the prop, how can one be weak and one strong? 40 is 40, right?

 

[jtexas]

Re: 2 or 3 cylinders, does it really matter?

.

 

[jim dozier]

Re: 2 or 3 cylinders, does it really matter?

The addition of more cylinders in any engine, 2-stroke or 4-stroke, does not directly correlate with more horsepower or more torque. It simply adds more firings per revolution which may make it smoother. A well balanced 12-cylinder engine will usually be a smoother engine than a well balanced 1-cylinder engine, but not necessariy more powerful. Perhaps Phatmanmike is confusing displacement with number of cylinders. If you take a 2000cc 2-cylinder engine and add another 1000cc cylinder you will get roughly 1/3 more power. If you take a 2000cc 2-cylinder and make a 2000cc 3-cylinder by redesigning it with three 666.7cc cylinders it may or may not make more power and may or may not be smoother depending on your port setup and balancing.<br /><br />All other things being equal (and they rarely are) displacement (cylinder volume) is the one parameter that directly correlates to power.<br /><br />It used to be that in dirt bike racing 1-cylinder dirt bikes were the engines with the most torque, but if you twiddle enough with any engine you can push the torque curves up or down the rpm range.

 

[Chinewalker]

Re: 2 or 3 cylinders, does it really matter?

Another thing to keep in mind. Not all horsepowers are created the same. Even two motors from the same manufacturer rated the same horsepower may not actually be making the same end power. I don’t know the percentage, but there’s a tolerance within the rating scale so that a motor that dynos at 38.2hp may be marketed as a 40hp, as can one that dynos at 42.1hp. In operation the one that actually turns 42.1hp will likely outperform the one that is actually only turning 38.2, even though their cowling both say 40 on them....<br />- Scott

 

[jim dozier]

Re: 2 or 3 cylinders, does it really matter?

In keeping with what Chinewalker says the same engine tested on a dyno at noon will put out 2 or 3% more or possibly less at midnight based soley on the variability of the dynamometer, and more importantly, the humidity and air temperature. You can count on a 1% increase in horsepower for every 10 degrees you lower (colder) the air intake temperature, although for extremes you would need to rejet.

 

[Forktail]

Re: 2 or 3 cylinders, does it really matter?

Here's how the manufacturers are required to rate their outboards...<br /><br />First they must declare an engine speed (at crankshaft). For example 5500 rpm.<br /><br />That declared speed must be the mid-point of the full throttle speed range recommended by the manufacturer for prop selection. For example 5500 rpm is the mid-point between a recommended 5000-6000 operating rpm.<br /><br />Their rated (for sale) power must be the full throttle power at the declared speed (at prop shaft), based on the corrected power on one or more engines. For example 150 HP at 5500 rpm.<br /><br />The corrected power will be the full throttle power as measured in a laboratory using a dynamometer and specified standards and correction methods.<br /><br />The highest power within the speed range, can not exceed the declared power by more than 6%. For example if an outboard is rated (declared) at 150 HP at 5500 rpm, it can not produce more than 6% additional HP at anywhere between the 5000-6000 RPM. 6% of 150 HP would be 9 HP. So the maximum HP this outboard could run would be 159 HP (presumably at 6000 RPM).<br /><br />Finally, the corrected power at rated speed must not deviate from the declared power more than +-10% or .45 KW (.33 HP), whichever is greater....except for engines more than 100 KW (74.6 HP) must not deviate more than +-5%.<br /><br />For example a 150 HP at 5500 RPM outboard must not have a corrected dyno power of more than 157.5 HP or less than 142.5 HP (+-5% of 150 HP).<br /><br />Another example would be a 50 HP at 5500 RPM outboard which could not have a corrected dyno power of more than 55 HP or less than 45 HP (+-10% of 50 HP)<br /><br />Yet another example would be smaller outboards where the .45 KW variation has a greater effect than the 10%. This applies to any small outboard under 3.3 HP. A 2.5 hp outboard could not have a corrected dyno power of more than 2.83 HP.<br /><br />Now you know, in part, why manufacturers can use nearly the exact same outboard for different HP classes. And now you know why some of us like to prop for the top of the RPM range.<br /><br />Remember, outboards are HP rated at their maximum range of RPM, not throughout their entire rpm range. Some outboards, which produce similar top end HP as others, can produce way more HP throughout the rest of the RPM range.

 

[seahorse5]

Re: 2 or 3 cylinders, does it really matter?

Finally, the corrected power at rated speed must not deviate from the declared power more than +-10% or .45 KW (.33 HP), whichever is greater....except for engines more than 100 KW (74.6 HP) must not deviate more than +-5%.

For example a 150 HP at 5500 RPM outboard must not have a corrected dyno power of more than 157.5 HP or less than 142.5 HP (+-5% of 150 HP).

Forktail's post is about how ICOMIA, the International Council of Marine Industry Associations, sets the standards for horsepower determination. Only the + or - 5% is incorrect.<br /><br />Under the ICOMIA Standard 28-83 "Power measurments and declarations for marine propulsion engines and propulsion systems" section 7 titled Manufacturing Tolerances, says that for marine engines or propulsion systems the tolerance is plus or minus 10% or .45 KW, whichever is greater, except for GOVERNED engines or systems above 100KW (75hp) which is plus or minus 5%. An outboard motor is considered an UNGOVERNED engine and is not subject to the 5% limit if it is over 75hp.<br /><br />Therefore, a 150 hp outboard can have an output of as high as 165hp or as little as 135 hp and still meet the industry standards. Every major outboard manufacturer uses the 10% factor.

 

[Forktail]

Re: 2 or 3 cylinders, does it really matter?

ICOMIA 28-83, Section 7<br /><br />"...except that for governed engines OR systems of more than 100 KW the tolerance shall be +-5%."

 

[waterinthefuel]

Re: 2 or 3 cylinders, does it really matter?

Wow, this post got alot more in depth than I thought it would. I sure learned alot here, anybody else can say the same?

 

[seahorse5]

Re: 2 or 3 cylinders, does it really matter?

Forktail's

--------------------------------------------------------------------------------<br />ICOMIA 28-83, Section 7<br /><br />"...except that for governed engines OR systems of more than 100 KW the tolerance shall be +-5%."

It is interpreted as "governed engines or [governed] systems over 100KW" which would not include outboard motors, as they are ENGINES that are NOT governed.<br /><br />Sorry, Forktail, you are reading it wrong. If you do not believe me ( but you will ), talk to Yamaha, Bombardier, Mercury, Suzuki, etc. and the NMMA.

 

[Forktail]

Re: 2 or 3 cylinders, does it really matter?

Already talked with ICOMIA (it's their standard).<br /><br />Seahorse, add whatever words you want to the standard, you would argue with me no matter what I posted.

 

[Forktail]

Re: 2 or 3 cylinders, does it really matter?

Seahorse, you don't seem to understand the difference between corrected power and declared power. <br /><br />You are wrong here.... <br /><br />

By seahorse - Therefore, a 150 hp outboard can have an output of as high as 165hp or as little as 135 hp and still meet the industry standards. Every major outboard manufacturer uses the 10% factor.

Following ICOMIA standard 28-83, Section 6.2, the highest power within the RPM range can not exceed declared power by more than 6%. If it does, both powers must be stated for that model.<br /><br />So you are wrong that a 150 HP outboard can have an output as high as 165 HP or as low as 135 HP. This would be well above the 6% limit, and that outboard would have to be dual rated (I don't know of any current one's that are).<br /><br />Corrected power (where any +-10% deviation allowance might occur) is obtained with an engine dynomometer at the engine. Declared power (where you claim a 150 HP outboard can really have an output of 165 HP) is obtained at the prop shaft.

 

[Forktail]

Re: 2 or 3 cylinders, does it really matter?

And since you didn't know, The ICOMIA Standard 28-83 you mentioned was subsided by ISO DIS 8665 - Small craft — Marine propulsion reciprocating internal combustion engines — Power measurements and declarations (Satellite standard ISO 8665).<br /><br />This standard would require a declared power deviation of no more than +-7% for spark ignition engines with a declared power of more than 50 kW (67 HP).

 

[catfish1]

Re: 2 or 3 cylinders, does it really matter?

popcorn anyone?

 

[kd6nem]

Re: 2 or 3 cylinders, does it really matter?

Tell me this- is every single outboard motor fully dyno'd before the horspower badge is placed on it? I am curious.

 

[Forktail]

Re: 2 or 3 cylinders, does it really matter?

Hi Bearcat. <br /><br />Nope, the test engine is only representative of the manufacturer's production units. That's why they will allow some tolerance.<br /><br />When tested, the outboard must be fitted with the exhaust system and all auxiliary equipment delivered with the unit, except the prop. <br /><br />Some parameters are controlled like coolant and fuel temp, etc. And there is some flexibility regarding carb wedges and exhaust piping in order to run the outboard in the proper position while being tested.

 

[seahorse5]

Re: 2 or 3 cylinders, does it really matter?

Declared power is what the manufacture "calls" their motor, such as a "150" and the rated rpm has to be in the middle of the full throttle operating range. Most engines have a 1000 rpm operating range, such as 5000 to 6000 rpm, with the max horsepower at 5500 rpm. Some engines only have a 500 rpm operating range such as 5500-6000 with max power at 5750 rpm.<br /><br />Corrected power (on outboards) cannot deviate more that 10% each way from the declared power. (ICOMIA Section 7)<br /><br />The bottom line is that manufacturers of today's outboards use the 10% rule with their production motors per NMMA (National Marine Manufacturers Association) procedures along with ICOMIA 28-83 standards. High performance models such as Yamaha's Vmax and Evinrude's HO series have horsepower outputs at the very top of the 10% limit. Most techs know this and the factories put out this information. <br /><br />Power standards were instituted years ago by the BIA (Boating Industry of America) to equalize manufacturer's claims. Merc engines back in the 50's put out much more hp than the sticker stated.