3 or 4 cylinders

[Lennyb5641]

Besides one extra cylinder what is the difference between a 3 and 4 cylinder outboard with the same horse power?

 

[boobie]

Re: 3 or 4 cylinders

The 4 cylinder will probably idle smoother.

 

[Silvertip]

Re: 3 or 4 cylinders

It isn't just about the number of cylinders. If both engines have the same displacement the four cylinder will have a smaller bore and/or stroke tha. those on the three cylinder.

 

[jimmbo]

Re: 3 or 4 cylinders

A three cylinder engine has some advantages over a 4 cylinder when it comes to exhaust tuning. It is easier to design a tuned exhaust to work over a greater RPM range on 3 than on a 4.

 

[roscoe]

Re: 3 or 4 cylinders

The number of moving parts, number of carbs, weight of the motor. cost of manufacturing.

 

[Chris1956]

Re: 3 or 4 cylinders

I had always heard that the odd number of cylinder engines worked better on 2 cycle motors. So the 3 cylinder 2 cycle motors would be good as would 6 cylinder motors. Just what I had heard....

 

[jimmbo]

Re: 3 or 4 cylinders

I had always heard that the odd number of cylinder engines worked better on 2 cycle motors. So the 3 cylinder 2 cycle motors would be good as would 6 cylinder motors. Just what I had heard....

Well not always. In the late 80s or early 90s Force built a 5 cylinder. It was no roaring hell

 

[Chris1956]

Re: 3 or 4 cylinders

Well, That was Force....maybe they messed up the design?

 

[Frank Acampora]

Re: 3 or 4 cylinders

OR maybe they didn't! My 150 five cylinder Force pushes my 21 foot cuddy at 42-45 MPH. I am quite happy with its performance.

Given a different displacement between the three and four cylinder engine, the four cylinder engine will develop more torque over the RPM range. THUS: AVERAGE horsepower will be higher. While top speed will be the same because, for example, 100 HP at 5500 RPM is 100 HP at 5500 RPM, no matter the number of cylinders, the time it takes to get to top speed will be less under full throttle acceleration.

I have proved this before with a three cylinder 90 HP engine and the same brand 4 cylinder 90 with 25 cubic inches more dis[placement. Both engines on the same hull reach the same top speed of 45 MPH but the four cylinder engine gets there a LOT faster. WAY better hole shot!

 

[jimmbo]

Re: 3 or 4 cylinders

Larger displacement engines of a given hp will have more low end torque and therefore quicker accelleration than a smaller displacement engine. Given a choice of a 3 cylinder or a 4 cylinder of the same hp and the same displacement I would choice the 3. Also given a choice of same hp and displacement between 4 cylinder or 6 cylinder I would choose the 6.

 

[Chris1956]

Re: 3 or 4 cylinders

Gee, so Jimbo likes the odd cylinder motors....who knew?

 

[jbjennings]

Re: 3 or 4 cylinders

Larger displacement engines of a given hp will have more low end torque and therefore quicker accelleration than a smaller displacement engine. Given a choice of a 3 cylinder or a 4 cylinder of the same hp and the same displacement I would choice the 3. Also given a choice of same hp and displacement between 4 cylinder or 6 cylinder I would choose the 6.

I don't understand, 6 being an even number, why would you want the 6 over the 4? I thought you said earlier that the 3 cylinder was good because it was an odd number? Just not fully understanding.
Are you meaning a v6 would be better than an inline 6? I always thought the Inline 6 by merc was a beast as far as torque and speed....
Just curious---I'm no outboard engineer by a longshot!
JBJ

 

[jimmbo]

Re: 3 or 4 cylinders

I said I prefer 3 cylinders over 4, and 6 over 4. Exhaust tuning wise, a 6 can be treated like 2 three cylinder engines. It is easier to engineer a tuned exhaust to provide benefit over a larger RPM range on a three cylinder engine than on a 2 or a 4.
Regarding inline 6 vs. V6... Both are 6s

 

[Chris1956]

Re: 3 or 4 cylinders

So to sum it up....for 2 cycle motors: 1 cylinder motors are lousy, 2 cylinder motors are OK, 3 cylinder motors are great, 4 cylinder motors are OK, 5 cylinder motors are nearly unknown and 6 cylinder motors are great.

Gee there was a V8 Johnnyride Outboard some years ago. Anyone have an opinion?

 

[jbjennings]

Re: 3 or 4 cylinders

Interesting....... thanks for the response. I have a 3 cylinder merc 65hp and it only has 2 carbs and is annoying to tune. I'm going to take the powerhead off and check for a leaky lower crank seal, since it has so much variation of rpms at idle. I had no idea that 3 cylinders was such a great thing for 2 stroke motors.

JBJ

 

[jimmbo]

Re: 3 or 4 cylinders

When I think 3 cylinders, I'm think of the the OMC models, which had 3 carbs. The 3 cylinder 49 cu in merc was an oddball which I forgot to mention in my post. I will admitt it was odd/poor engineering on Mercurys part. Mercs induction system, which had a carb between 2 cylinders, was fine on engines with 2, 4, and 6 cylinder but it wasn't the best on a 3. Exhaust wise it was like any other 3.

 

[jbjennings]

Re: 3 or 4 cylinders

The only 3 cylinder motors I've run were a '70 60hp OMC and my '98 yamaha 90hp and indeed they were/are smooth running engines with good acceleration at all rpms. I had no idea it had to do with exhaust tuning. My old 3 cylinder mercs are pretty nice motors other than at idle, and I'm sure it's because of the carb sharing as you said.....
Later,
JBJ