Twin cylinder v single cylinder.

[munster1967]

Hi folks.
What's the difference between a twin cylinder and a single cylinder 2.5 HP 2 stroke outboard?. Are there any performance differences??

 

[RivalRedwing]

surprised that there are any twin cylinder 2.5 hp engines out there....

 

[munster1967]

The Johnson 2.5 twin cylinder. Mid 90s .

 

[munster1967]

surprised that there are any twin cylinder 2.5 hp engines out there....

 

[RivalRedwing]

I stand corrected, there is at least one

 

[munster1967]

I stand corrected, there is at least one

Yes indeed. What would be the advantages with a twin cylinder over a single cylinder in general. ?

 

[vyv_cox]

The Johnson 2.5 twin cylinder. Mid 90s .

I owned one of these and found it to be excellent. Good starter, smooth and powerful. Unfortunately it was stolen from our dinghy when we were having a meal in a pub at Menai Bridge. I reported its theft to the police, who could not have been less interested.

 

[munster1967]

Ok. I never knew there was a 2.5 HP twin cylinder until this week. Sorry to hear it was stolen ! I presume there aren't too many around. ? Would you recommend it over a single cylinder?

 

[garymalmgren]

A twin cylinder will be heavier, smoother, use more fuel and be slightly easier starting.
For service you will need to shell out for two spark plugs.

A single will be more modern and parts will be available.

RE: Would you recommend it over a single cylinder?

The condition of the engine will be the deciding factor. More than price even.
There is such a thing as false economy.

What I am saying is get a good reliable engine!

gary

 

[munster1967]

A twin cylinder will be heavier, smoother, use more fuel and be slightly easier starting.
For service you will need to shell out for two spark plugs.

A single will be more modern and parts will be available.

RE: Would you recommend it over a single cylinder?

The condition of the engine will be the deciding factor. More than price even.
There is such a thing as false economy.

What I am saying is get a good reliable engine!

gary

A little more powerful or same performance??

 

[vyv_cox]

Ok. I never knew there was a 2.5 HP twin cylinder until this week. Sorry to hear it was stolen ! I presume there aren't too many around. ? Would you recommend it over a single cylinder?

It was certainly lighter than a single cylinder 4-stroke. I don't recall it being much heavier than a single cylinder 2-stroke but I was younger and fitter then . But this was a long time ago, are there any in production now?

 

[munster1967]

It was certainly lighter than a single cylinder 4-stroke. I don't recall it being much heavier than a single cylinder 2-stroke but I was younger and fitter then . But this was a long time ago, are there any in production now?

I don't know if there are any in production now tbh. I currently have a 2 HP dt2 suzuki and I'm looking for a bit more power without too much extra weight and was looking at 2.5s in general.

 

[garymalmgren]

A little more powerful or same performance??

2.5 HP is 2.5 HP. Not much in the way of power or performance.

gary

 

[munster1967]

A little more powerful or same performance??

2.5 HP is 2.5 HP. Not much in the way of power or performance.

gary

Ok thank you.

 

[AntarcticPilot]

A little more powerful or same performance??

As both have the same power rating, there's no difference that way; they both have the same power output.

It's possible that one will generate more torque than the other; that's a matter of the rpm at the propeller - slow revving is better for displacement craft, as it transfers the engine's power into forward motion better for an inherently slower hull form. High revving is better for planing hulls.

I'd expect a 2 cylinder engine to be smoother running than a single cylinder engine.

 

[munster1967]

A little more powerful or same performance??

2.5 HP is 2.5 HP. Not much in the way of power or performance.

gary

Ok. Perhaps a 3-3.3 HP 2 stroke might be better option. I currently have a dt2 2 HP.

 

[38mess]

I wonder if they used the same engine for say a 5hp, be easy to do.

 

[B27]

I think these are all over 20 years old?
So many will be dead, many will be corroded messes, faulty etc.
If you find a good outboard at a good price and it meets your needs, then I wouldn't worry whether it's a twin or a single.


People will tell you '2.5 HP is the same whether it's twin, single, two stroke or four', but it's not.
Some engines have more torque/power at lower revs. My Yamaha 2HP needs to be revving to deliver much thrust, on a heavy boat it bogs down and can't rev enough to develop much power. A 2.5HP 4 stroke I have was better from this point of view.
The prop also makes a difference, you can get alternative pitch props for some outboards.
If you're finding you just don't have enough power, consider a change of prop, or look for a real increase like a 5HP.


IIRC those Johnson twins were quite quiet, compared to say my Yamaha 2?

 

[VicS]

The Johnson 2.5 twin cylinder. Mid 90s .

I think you will find that if it is a 2.5hp model it dates from 1987 or 1988

Throughout the 1990s a similar 3 hp was produced.

If you post the model number, probably beginning J3R followed by 3 or more other letters, ( but not the serial number) its year of manufacture can be identified

 

[munster1967]

I think these are all over 20 years old?
So many will be dead, many will be corroded messes, faulty etc.
If you find a good outboard at a good price and it meets your needs, then I wouldn't worry whether it's a twin or a single.


People will tell you '2.5 HP is the same whether it's twin, single, two stroke or four', but it's not.
Some engines have more torque/power at lower revs. My Yamaha 2HP needs to be revving to deliver much thrust, on a heavy boat it bogs down and can't rev enough to develop much power. A 2.5HP 4 stroke I have was better from this point of view.
The prop also makes a difference, you can get alternative pitch props for some outboards.
If you're finding you just don't have enough power, consider a change of prop, or look for a real increase like a 5HP.


IIRC those Johnson twins were quite quiet, compared to say my Yamaha 2?

Thank you for your reply. And all the information. Yes I have heard the 2.5 HP Yamaha 1 cylinder beats all the other current 2.5 HPs for performance. I don't fancy the weight of a 5 HP for lifting on and off each trip.