2 or 3 cylinders, does it really matter?

rickdb1boat

Supreme Mariner
Joined
Jan 23, 2002
Messages
11,195
Re: 2 or 3 cylinders, does it really matter?

Me, too! Wish I would have never posted at all....
 

Forktail

Ensign
Joined
Feb 11, 2002
Messages
977
Re: 2 or 3 cylinders, does it really matter?

seahorse, you're in over your head. <br /><br />And you still haven't figured out the difference between horsepower at the crankshaft, horsepower at the propshaft, corrected power, and declared power...and how they relate to the standards.<br /><br />BTW, the standards you listed relate to emissions and the EPA. :rolleyes: <br /><br />
They do not use ICOMIA except for the duty cycles.
From Bombardier...<br /><br />"Power Ratings: Johnson outboards are power rated in accordance with NMMA procedure using the International Council on Marine Industry Associates (ICOMIA) standard 28/83."<br /><br />"Power Ratings: Evinrude outboards are power rated in accordance with NMMA procedure using the International Council on Marine Industry Associates (ICOMIA) standard 28/83."<br /><br />Duty cycles? :D LMAO :D
 

Hunky Dory

Petty Officer 2nd Class
Joined
Jul 20, 2003
Messages
102
Re: 2 or 3 cylinders, does it really matter?

Only a fool would deign to comment after all the enjoyable insights above -- so here goes: The answer to the original question (remember the original question?) is clearly "anything the engineers want it to be". Torque is how hard you twist the shaft. How often per minute that you twist the shaft that hard makes horsepower -- and smoothness. So, 40 Horsepower at 1500 rpm is a gob more torque (and impact) per fire in the hole than 40 horsepower at 6000 rpm. You can build a 2, 3 or 12 cylinder engine for torque at low or high rpm. That makes the 2, 3 or 12 cylinder engine the clear winner! What was the race?<br /><br />Fuel economy is a measure of efficiency and that discussion is not limited by cylinder count. If you ever compared mpg on identical Chevy trucks with identical displacement pre and post Vortec you have more insight into that complexity than most. Even more if you then traded your Chevy for a Dodge like somebody I know...<br /><br />Generally, higher displacement per cylinder (same displacement per engine) has been related to most low end torque while smaller cylinders and great breathing makes for high rpm -- high horsepower. Think Buick and Ferrari. <br /><br />Or try motorcycles, say 250cc; high torque at low speed comes with one cylinder trials bikes that can be ridden over a Volvo wagon at 1 foot per second. High horsepower at high speed comes with 4 cylinder GP bikes that hit 130 mph every lap. Having said that, big GP bikes are revisiting 2 cylinders w/o giving up speed. Thought that might clear things up...<br /><br />On a planing hull a torque curve imbalance can be quite visible since few boats have shifting transmissions. Some struggle to get on the step and then go like scat – meaning inadequate mid range torque compared to top end horsepower. Here at altitude I've watched a 60+ mph fire breathing V8 flatbottom take 20 seconds to make 20 mph ("peaky") -- and a 24' 4 cyl. outboard pontoon make 20 in 4 seconds and then top out at 22 ("torquey"). Put a prop of the pontoon's pitch (better be much bigger diameter for this silly game) on the ski boat and it'll hit 20 in 1 second -- and then top out at 24 ("goofy"). One assumes that the ski boat came with enough midrange torque at sea level to step quickly on-plane and then hit 80 ("aah")<br /><br />Back to Buick and Ferrari: More cylinders seem to cost more money -- how smooth do you want your engine to run?<br /><br />Search words: P--- up a rope, dumb as a stump, smacked head on rock, reading it wrong, would-be expert, just plain deviant, irrelevant fraud and skinned-knuckle charlatan. Just tryin’ to help...
 

seahorse5

Rear Admiral
Joined
Jan 24, 2002
Messages
4,698
Re: 2 or 3 cylinders, does it really matter?

Forktail,<br /><br />Bottom line is that all 3 major manufacturers use the 10% tolerance in output horsepower for production outboards. <br /><br />Merc is also touting that top horsepower allowance with the introduction of "Project X" next Thursday at the Miami Boat Show. It's at 10:15 am if you want to make it.<br /><br />No use "highjacking" this thread anymore whose initial request was about torque, I'm outa here.<br /><br />I'll be out of town for the next two weeks, so have fun playing by yourself.<br /><br />Perhaps when I return you might want to start a discussion why the customer does not get the horsepower he paid for, because in most cases, he gets more.
 

Clams Canino

Commander
Joined
Jan 10, 2004
Messages
2,179
Re: 2 or 3 cylinders, does it really matter?

Aside from the rest of the blather on this thread :D THREE cylinders is the best "natural configuration" for a two stroke. Both the inline six and the v six are set up (exhaust wise) as two banks of three. <br /><br />Not even a close call: a three is a more efficiant powerplant than a twin, everything else being equal.<br /><br />-W<br /><br />
Originally posted by waterinthefuel:<br />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?
 

jim dozier

Lieutenant Commander
Joined
Jan 8, 2003
Messages
1,970
Re: 2 or 3 cylinders, does it really matter?

Clams are you referring to thermal or volumetric efficiency or both. And precisely why is the 3 more efficient than the 2? Could you please define the term "natural" as applied to a machine.
 

Clams Canino

Commander
Joined
Jan 10, 2004
Messages
2,179
Re: 2 or 3 cylinders, does it really matter?

A three cylinder motor fires 120 degrees apart. <br /><br />120 degree exhaust pulse timing is optimal for two stroke exhaust tuning.<br /><br />-W
 

vidar

Petty Officer 2nd Class
Joined
Jun 30, 2003
Messages
165
Re: 2 or 3 cylinders, does it really matter?

as long as the motor goes BROOOOOM........ :rolleyes:
 

Keith Thomas

Recruit
Joined
Feb 7, 2004
Messages
3
Re: 2 or 3 cylinders, does it really matter?

This may be helping me with my question about an older 3 cyl Merc rated at 90 HP @ 71cc versus the new 3 cyl Merc rated at 90 HP @ 85cc. Are any of the power tests/curves related to in this thread available on line or elsewhere?
 

Clams Canino

Commander
Joined
Jan 10, 2004
Messages
2,179
Re: 2 or 3 cylinders, does it really matter?

This power vs ci difference may be due to powerhead vs propshaft hp ratings.<br /><br />And for Jim, I forget WHICH it is, but it's either that the exhaust pulse hits at exactly the right time to stop the next charge from getting out the exhust ports of the 2nd cylinder, OR that you get the best exhaust scavenging from the 3rd cylinder. <br /><br />I'm pretty sure its the first one.<br /><br />-W
 
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