# A Case for Small Displacement Twin Cylinder Engines ???



## tpenfield (Feb 24, 2015)

My experience with re-powering and using snowblowers has got me thinking . . . (and that can be dangerous  )

Anyway, I do my fair share of boating once the snow melts and work on my various boat engines, etc. One thing I notice about the 2 small outboard motors that I have (4 HP Johnson and 7.5 HP Mercury) is that they both have 2 cylinders, even at that low power.

Certainly the twin cylinder design give a more even power and can handle loads better (barring the fact that they are 2 stoke as well). 

Taking that concept of 2 cylinders at small displacement into the snowblower world, it seems like a twin cylinder approach should yield smoother operation and better ability to handle snow throwing loads versus our single cylinder engines that are so common.

Thoughts, ideas . . . :icon_scratch: is there such a machine, like a 250-300cc twin cylinder snowblower engine?


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## ELaw (Feb 4, 2015)

I'd love to see such an engine. It would vibrate less, and probably be easier to pull-start since the effort to get past each compression stroke would be half.

Of course there are downsides too. I'd expect a 2-cylinder engine to take up more space than a single of the same displacement. The ignition system becomes more complex, and you need "real" intake and exhaust manifolds (or two carbs or mufflers).


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## e.fisher26 (Nov 6, 2016)

I think the size alone would make it hard to fit with out moving handlebars. The harbour freight twin horizontal is a big engine 


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## tpenfield (Feb 24, 2015)

e.fisher26 said:


> I think the size alone would make it hard to fit with out moving handlebars. The harbour freight twin horizontal is a big engine


the thing about most twin cyl horizontal shaft engines today are that they are twice the size (600cc ish) and twice the power (20+ HP) than we need. Wondering if there is such a thing as a twin cylinder in the 250-300cc range . . . I think small dirt bikes might have twins in that size range (maybe)?


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## e.fisher26 (Nov 6, 2016)

Besides the need to add cooling and figure out shaft size 


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## JLawrence08648 (Jan 15, 2017)

Would the single cylinder have more torque than the same cc size as two cylinders?


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## e.fisher26 (Nov 6, 2016)

One larger cylinder compared to 2 smaller ones.... I don't know 


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## ELaw (Feb 4, 2015)

The single-cylinder would have twice the peak torque (during a power stroke) as the two-cylinder, all other things being equal. But the two-cylinder engine would have twice as many torque pulses during any given amount of time (I'm talking minutes/hours here not milliseconds) so the work done would be equal.

I suspect the major barrier to two-cylinder engines is cost. For example since most of the cost is machining, a piston for a 150 cc engine costs nearly the same as a piston for a 300 cc engine. So the cost of pistons for your 300 cc twin will be nearly double that of the single. And that goes for a lot of other things like cylinder heads, the cylinders themselves, and valvetrain components. So you'd end up having to charge a lot more for your 2-cylinder engine that makes X horsepower than a single that makes the same horsepower.

I imagine that's why twins are so much more common in the next power bracket up. It makes sense to people that a 20 HP engine would cost twice as much as a 10 HP engine, even though the cost is related more to the component count than the actual horsepower output.


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## tpenfield (Feb 24, 2015)

JLawrence08648 said:


> Would the single cylinder have more torque than the same cc size as two cylinders?


Not really, hard to tell . . . 

The big difference that I see is that with a single cylinder (4-stroke) engine, you are getting 1 power stroke for every 2 rotations of the engine. The engine is relying on momentum for 1-1/2 revolutions and power on the remaining 1/2 revolution.

With a twin cylinder you get 1 power stroke for each revolution of the engine, each being 1/2 of the revolution. . . therefore smoother operation, less reliance on momentum.

That may add up to similar or even more torque . . . the mass of the flywheel would even have some effect, I would think.


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## drmerdp (Feb 9, 2014)

tpenfield said:


> Not really, hard to tell . . .
> 
> The big difference that I see is that with a single cylinder (4-stroke) engine, you are getting 1 power stroke for every 2 rotations of the engine. The engine is relying on momentum for 1-1/2 revolutions and power on the remaining 1/2 revolution.
> 
> ...


That all sounds tight to me. 

Other then for smoothness, I'm not sure a two cylinder would do anything other then take up more space and cost more. 

I certainly appreciate my twin cylinder tractor over my single cylinder tractor rated at similar power.


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## tpenfield (Feb 24, 2015)

It seems that the types of small twin engines that are around are for . . . large scale R/C planes, outboard motors, scooters.


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## RedOctobyr (Mar 2, 2014)

Agreed, I think a twin would be cool, but not sure if it would be compelling enough to justify the extra cost. Let's face it, snowblowers are already rather expensive as it is. Now, if someone got a small twin, and wanted to mount it to a nice machine with a blown engine, that would be cool. 

drmerdp, I had a tractor with a Briggs 14.5hp OHV single-cylinder, and now have one with a Briggs 18hp flathead twin-cylinder. The twin is more powerful, not surprisingly, but also smoother and quieter. I speculate that it may be quieter in part because each exhaust pulse is from a smaller cylinder, and so is a smaller blast. I'm sure it uses more gas than the smaller single-cylinder, but I don't use much anyhow, so I'm not worried. I like the twin for that application. 

I do spend a lot more time on the tractor per year than I do with the blower, so it being smoother and quieter benefits me for more runtime than clearing the driveway. Admittedly, I mow during "normal" hours, while you often have to clear in the morning or at night, so a quieter blower would, of course, have appeal.


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## RIT333 (Feb 6, 2014)

I have a 50 yr old Evinrude 3 hp, and it is 2 cylinders. It runs fantastic, and pushes a fairly heavy fishing boat (180 lbs) and two people (300 lbs) at 8 mph ! It is a 2 cycle, by the way. Polutes like crazy, but Trump doesn't care.


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## Blosumsno (Dec 7, 2016)

This is the smallest twin I could come up with: Brand New Engines | Briggs & Stratton Horizontal 13 HP Vanguard 1" x 2-29/32 Tapped 3/8 #295347-0191

Sure would look cool tho.

Then there's this:


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## justintendo (Jan 2, 2017)

a twin will definitely be heavier, take up more room, and cost more to make...
on the plus side however...it will be quieter, smoother, and have the potential to last longer. 
im sure having the larger physical size of the twin will cause some design issues with the rest of the blower. a twin for a bigger two stage would likely be pretty neat and super smooth.


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## drmerdp (Feb 9, 2014)

Quieter is another good point. Unless your yamaha and encase the engine in a sound dampening weatherproof enclosure.

Particularly jealous of that...


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## Geno (Nov 29, 2011)

I like my twin cylinder Honda 20 on my blower- so smooth. plenty of umph but usually just above idle is all that is needed. Way overkill and as mentioned size is a factor. in my case weight was too as I had too put pillow blocks on outside of body too support extra weight. was originally a 8-32 Arien's. 3+ years now and never misses a beat. Pull start always, in fact took starter off and have small battery tray where starter use to sit to control electric chute. I'd not think twice on a factory twin blower if were ever produced and I was in market for new blower.


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