4cyl vs. 3cl vs. 2cyl?

[biscayn8]

First post to the forum-

I recently sold my gheenoe and am in the market for a larger skiff or john boat for flats fishing. I've been looking around for a used outboard, too. 40hp sounds about right.

I've noticed that most outboards in this hp range are 3 cylinders. However, some are 2 cylinders and I've even seen a 40hp Mercury with 4 cylinders.

What are the advantages/disadvantages to these 3 configurations?

 

[Silvertip]

Re: 4cyl vs. 3cl vs. 2cyl?

Four cylinder is likely the smoothest, then three, then two. Performance will be about equal. 40 HP is 40 HP. Fuel economy will likely be less on the twin, then the three then the four, but at wide open throttle they will all be about the same. 40 HP is 40 HP and it takes so much fuel to make that power.
Four cylinder has more stuff to go wrong. Then three then two.
Four cylinder will likely be heavier, then three then two.
It all depends on year make and model you are comparing.

 

[tashasdaddy]

Re: 4cyl vs. 3cl vs. 2cyl?

i have ran, 2 cylinder 30,40,50's JohnnyRudes all my life. tuned properly never had problem.

 

[JB]

Re: 4cyl vs. 3cl vs. 2cyl?

I agree with TD. The JohnnyRude twin loopers are very good engines, and i think the 40 is the best (least stressed).

 

[TOHATSU GURU]

Re: 4cyl vs. 3cl vs. 2cyl?

Everything else being equal...The hole shot and fuel economy at given RPM's will be different.

 

[biscayn8]

Re: 4cyl vs. 3cl vs. 2cyl?

Tohatsu Guru- How would the holeshot differ?

Thanks for the responses, guys.

 

[mthieme]

Re: 4cyl vs. 3cl vs. 2cyl?

If you go used and talking about a package - you take it or leave it. I wouldn't let the number of cylinders be a deciding factor. The biggest factor to me would be maintenance. The more cylinders, the more maintenance.
If you talking new (where you will have a choice) - here are your choices...
Mercury - 3 cylinder
Evinrude - 2 cylinder
Yamaha - 4 cylinder
Honda - 3 cylinder
Tohatsu - 3 cylinder
Nissan - 3 cylinder
Suzuki - 3 cylinders

Personally, I don't think the number of cylinders is going to make a bit of beans pushing a jon boat. As long as you maintain it, any of them will do just fine.
I've had more 2 cylinder outboards than any other - 3 at the moment.

 

[jay_merrill]

Re: 4cyl vs. 3cl vs. 2cyl?

Tohatsu Guru- How would the holeshot differ?

Thanks for the responses, guys.

Holeshot is a function of torque and, for a given displacement, the fewer the number of cylinders, the more torque will be developed. This is why motocross motorcycles are typically one cylinder, and "bigtruck" engines are six cylinders, and sometimes even four cylinders.

 

[TOHATSU GURU]

Re: 4cyl vs. 3cl vs. 2cyl?

Everything else being equal...The number of cylinders makes a huge difference in hole shot. More initial power is available in an engine with more cylinders as the engine does not have to work as hard to turn the prop as an engine with less cylinders. However, as RPM's increase, the multi cylinder engine loses it's advantage by the time it reaches max RPM. Keep in mind though that different technologies can negate that fundamental idea. For instance:

A carbed, 3 cylinder four-stroke of x hp will not have as much hole shot as a carbed, 3 cylinder two-stroke of the same hp.

A EFI, 3 cylinder four-stroke of x hp may have as much hole shot as a carbed, 3 cylinder two-stroke of the same hp.

A DFI, 2 cylinder two-stroke of x hp will probably have as much hole shot as a carbed, 3 cylinder four-stroke of the same hp.

A DFI, 2 cylinder two-stroke of x hp will not have as much hole shot as a DFI, 3 cylinder two-stroke of the same hp.

Of course the differences may not be observed in some applications due to other factors....But, in general it's a fact a life.

For flats fishing, where hole shot is important, a 2-stroke engine would be more desirable than a four-stroke and a three cylinder would be more desirable than a two-cylinder...Except you also have to look at engine weight. Factor in what an engine weighs and the number of cylinders may be a complete wash.

 

[Silvertip]

Re: 4cyl vs. 3cl vs. 2cyl?

There are no absolutes here. Holeshot, fuel consumption, top speed and any other measure of performance is a combination of design factors and is not limited to the number of cylinders. Lower unit gear ratio determines to a large extent how large a prop diameter can be run and what the most effective pitch range is for that engine. Evinrude E-tec mid range engines (40-50-60 HP) for example run 2.67:1 gear ratios and swing 13-1/4 inch diameter props with 17 - 19 inches of pitch. Four stroke equivalents from other manufacturers would tend to run much less gear which allows faster prop speed but smaller diameters and less pitch to get them out of the hole. A three cylinder 40/50 HP Merc has a 1.83:1 gear set and typically run a 10-1/2 x 13P. A two stroke "generally" will out-hole shot an equal four stroke. One of my previous boats had a 40 HP Evinrude 2S) on a 16 foot V-hull. I fished with another couple who had a very similar boat with a 50 HP Merc three cylinder (2S). Although the Merc was faster than my Evinrude, my boat would pop on plane much quicker than his. And when I say the Merc was faster, it was by about 2 MPH. So much for the 2 vs 3 vs 4 cylinder having an advantage on hole shot. I routinely see boats with relatively large engines that really struggle to get on plane but once they do, they go like nuts.

 

[TOHATSU GURU]

Re: 4cyl vs. 3cl vs. 2cyl?

"So much for the 2 vs 3 vs 4 cylinder having an advantage on hole shot."

And that's why I said:

"Everything else being equal...The number of cylinders makes a huge difference in hole shot."

Equal being the point at which it does make a huge difference.

 

[biscayn8]

Re: 4cyl vs. 3cl vs. 2cyl?

For flats fishing, where hole shot is important, a 2-stroke engine would be more desirable than a four-stroke and a three cylinder would be more desirable than a two-cylinder...Except you also have to look at engine weight. Factor in what an engine weighs and the number of cylinders may be a complete wash.

Engine weight is an important consideration. I'm suprised to see how heavy some of the DI two-strokes are!

 

[mthieme]

Re: 4cyl vs. 3cl vs. 2cyl?

66 # for a Merc.
That's three cases of beer iced down !!!
or 11 gallons of fuel (+/-).
or that second battery.
or me after Thanksgiving pig fest!

 

[Silvertip]

Re: 4cyl vs. 3cl vs. 2cyl?

So you contend that given three engines (a twin, a triple and a four cylinder) all with the same displacement, same gear ratios and same prop diameter and pitch, mounted on the same exact hull that the 4 cylinder will out hole-shot the three and the twin -- without exception?

 

[TOHATSU GURU]

Re: 4cyl vs. 3cl vs. 2cyl?

I contend that if everything else is equal, a 4 cylinder engine will certainly will have more hole shot than a 3 cylinder engine. We really are not in disagreement as the number of cylinders is but one in a list of factors. You have said it. I have said it. I'm not saying that's it's the most important factor...It just needs to be taken into fair consideration. My only difference with you, apparently, is that you don't seem to think it is a factor at all. I disagree with you. Whether the number of cylinders is critical in any given comparison of two outboards is subject to that comparison alone. Regardless, I don't want to argue about it as I know I'm right....And you know your right and neither one of us is going to change their mind

 

[jay_merrill]

Re: 4cyl vs. 3cl vs. 2cyl?

I gave a simple example that ignored many of the things that Silvertip correctly pointed out. There are indeed, many more things that affect torque in an outboard motor.

That said, generally speaking, if you had a motor with fewer cylinders, but everything else was the same or substantially the same, that motor should offer more torque. I think horsepower and torque are being confused here and they are quite a bit different. In the the automotive world, for example, if your are looking for speed, you will be interested in an engine's horsepower rating. If it is a truck that will be towing that big boat you just bought, you will be more interested in torque.

Hole shot is a condition where the "load" is going to resist the effort of the prop to rotate and move water. In that condition, torque is exactly what is needed and it is needed at a time when the motor is operating at low rpm. Generally speaking, an engine with fewer cylinders will handle that situation better. I see no reason (other than geaing, fuel delivery, 4S v. 2S, etc) why this should not be true in an outboard.

 

[mthieme]

Re: 4cyl vs. 3cl vs. 2cyl?

HP is calculated from torque. HP=torque*rpm/5252.

How do you determine that fewer cylinders provides more torque?

 

[Silvertip]

Re: 4cyl vs. 3cl vs. 2cyl?

Don't misunderstand -- I was only looking for clarification of "all things equal" because that's a near impossibility with engines from various manufacturers. However, just because an engine has four cylinders and another engine of exactly the same displacement has two cylinders does not give the 4 banger an advantage. Displacement (cubic inches/cc's) is a function of bore diameter, stroke, and number of cylinders. For example, you can certainly have an 800 cc two cylinder, 800 cc three cylinder and an 800 cc four cylinder. That makes them equal. Now if you meant you were comparing 40 HP (or any other HP) engines with no regard for displacement, then yes, the four banger would likely have an advantage since it likely has more displacement even though "all other things are equal". Torque generally follows displacement and is not totally a function of number of cylinders. Engines with a high cylinder count must have smaller bores or shorter strokes (or both) than engines with fewer cylinders. Conversely, the fewer number of cylinders (2 or 3) to achieve the same displacement as a four cylinder means the bore and stroke (either or both) must be larger to achieve that displacement. You know that of course and all of this is simply an attempt to help others understand. Peace

 

[jay_merrill]

Re: 4cyl vs. 3cl vs. 2cyl?

I would defer to people with true scientific knowledge of engine design on the answer to why engines with fewer cylinders tend to have more torque, all other things being equal. My guess is that it has to do with the bore of the cylinders. While stroke can vary too, there isn't as much likelyhood of significant difference in stroke, as there is in bore. With that in mind, I would think that large bore cylinders tend to create more low rpm "grunt," than smaller bore cylinders.

One exception that I can think of to this assumption, however, is a motor that is designed such that two cylinders (4 or 6 cylinder) fire at exactly the same time. Frankly, I have no idea if such a thing exists in the outboard motor world, but if so, what you would have is a multiplied effect in terms of power pulse.

There was a time when many "big trucks" (straight trucks, tractor trailer power units) had 8 cylinder diesels. The Cat 3208 is an example of this. For quite some time, however, such engines are the exception rather than the norm. Look under the hood of a Peterbuilt, Kenworth, Freightliner, Sterling, etc., and you will almost always find a straight six engine. As I mentioned before, there is even a 4 cylinder diesel (Detroit Series 50) that can be found in a few tractors. I have a friend who has a Freightliner FL112 that has one. These motors are used because they develop lots of low rpm, brute force.

While HP may be calculated from a formula that includes a torque value, that does not make them the same thing. To end up with a hp value, you start with a torque value, but that value and where it peaks in the power band, is an entirely different issue. Although I haven't looked at any torque v. HP power curves lately, I think that most would indicate that peak torque and peak HP occur at different points in the power band of almost any engine.

I enjoy these discussions because I love to dig into what makes things tick. I am a self described "information junkie." That said, since this thread is about motors in the 40hp range, I don't think there is going to be a significant amount of difference between any of the motors that the OP might choose.

 

[mthieme]

Re: 4cyl vs. 3cl vs. 2cyl?

Any leads?