twin cylinder vs single cylinder torque- which has more?

I'm having a "discussion" with a friend over which motor will produce more low rpm torque-

I say single cylinder motors only have a power stroke for one out of every 2 complete revolutions of the crank, whereas a twin cylinder has a power stroke every complete revolution of the crank. (or- for every 4 strokes of a single, there's one power stroke 1/4 - for every 4 strokes of a twin, there's 2 power strokes 2/4) producing max torque in low range.

So- a twin will always produce more torque then a single of the same cc in regards to low range rpm- I also figure there's more inertia in a twin cylinder motor-

Twin cylinder = twice as many power strokes per time then a single cylinder = more inertia = more power = more resistance required to stall the engine = more torque in the twin.

Again, we're talking about torque, not HP- all else being equal like fuel delivery, displacement (cc) and application.

Please don't give me formulas! I'm not looking for that, just a simple answer from a mechanical engineer or motor brainiac!



Here's the correct answer- posted by another guy from another post.

Torque is twisting force -- pounds of pressure multiplied by the length of your leverage.

All things being equal, the pressure of the burning fuel-air mix will be equal between a single and a twin -- the same pounds per square inch. To get pounds of force pushing down on the piston you multiply the PSi by the area of the piston. The single has the larger piston diameter and thus the greater downforce.

The twisting force (Torque) is this downforce applied through the lever that is the crank. The single has the longer stroke so it's greater downforce is multiplied by a longer lever to produce even greater torque.

The number of cylinders gives you a more even application of power, and the smaller cylinders allow higher RPMs for much greater power -- but for brute twisting grunt torque the single cylinder rules. Which is why dirt bikes, where torque is at a premium, are mostly singles.

4 Answers

  • 1 decade ago
    Favorite Answer

    I don't think it's that simple, it depends on other factors.

    Assuming the two have the same displacement....

    If you plot torque versus rotation for each, they both have different curves, with the single having one larger peak vers two smaller peaks for the dual. If you averaged out the torque for each over several rotations, I suspect that average will come out the same or close.

    But the single requires a larger flywheel, which means more weight, heavier bearings, more friction. The dual has twice as many bearings and valves and rings, which adds friction. Gets complicated.


  • 1 decade ago

    Sorry but the more displacement the more torque at any speed. Compression ratio also enters into the equation as well as the fuel used and the ability of the engine to ingest oxygen.

    More cylinders may make the engine run smoother and have a bit more even power or torque output but on a dyno the factors above determine the out come and not the number of cylinders.

    Source(s): the laws of physics.
  • kasab
    Lv 7
    1 decade ago

    If you consider two engines of different design but of the same number of cylinders and the same c.c. capacity, would they produce the same torque or torque - speed characteristic? The answer is "No". I think your whole argument has no base.

  • Anonymous
    1 decade ago

    There are exceptions- but in a nutshell, you're right.

    I'd give you the formula's, but you don't want them.

    Source(s): mechanical engineering grad student
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