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Type II "Twingle"?
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brewsky
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Joined: 23 Jul 2008
Posts: 1515
Location: Princeton, WV

PostPosted: Sat Nov 28, 2009 7:08 am    Post subject: Reply with quote

G-Man wrote:


You get more peak torque at the instant when two pistons are pushing simultaneously.


G

Exactly!

G-Man wrote:
"Don't forget though that you have another stroke where nothing is happening at all. Therefore the average torque available for acceleration will be pretty much the same
"
True, but now you are inserting Time into the mix, and therefore leaving the definition of Torque.

Practically speaking, it's the difference in snapping the throttle open @ 1500 RPM on your Matchless verses your CB400F.

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G-Man
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PostPosted: Sat Nov 28, 2009 7:09 am    Post subject: Reply with quote

If you re-phase the cranks on a bicycle to be in line with each other you will get the same effect. Two legs pushing at once will increase the 'torque' for half a stroke, but then what happens?

G

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brewsky
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Joined: 23 Jul 2008
Posts: 1515
Location: Princeton, WV

PostPosted: Sat Nov 28, 2009 7:51 am    Post subject: Reply with quote

G-Man wrote:
If you re-phase the cranks on a bicycle to be in line with each other you will get the same effect. Two legs pushing at once will increase the 'torque' for half a stroke, but then what happens?

G

My point exactly!
You will be able to move the first few feet much easier, but it wont get you thru the 1/4 mile any faster.
The practical difference is the ability to lug around in slow speed traffic in a more controllable manner at lower RPM.
Which is easier to ride around in slow speed traffic, The Matchless or the CB?

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G-Man
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PostPosted: Sat Nov 28, 2009 12:25 pm    Post subject: Reply with quote

Well - it's the CB for traffic, very smooth. The Matchless needs a great big flywheel to smooth out those power strokes (the time element). Without big flywheels the Matchless would be completely unrideable, whereas the 400 with it's four little pulses, evenly spaced will run with minimal flywheel, down to walking speed

If you snatch the throttle open on the Matchy when it's on the wrong stroke, it'll probably just stall. It's the flywheel that makes a single appear torquey as it stores up the energy from the power stokes and delivers it more gradually to the wheel. Take a look at a single cylinder steam engine when you get a chance. Massive torque on the power stroke but won't even make it to the next one without a big flywheel to store the energy.

G

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brewsky
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Joined: 23 Jul 2008
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Location: Princeton, WV

PostPosted: Sat Nov 28, 2009 1:55 pm    Post subject: Reply with quote

G-Man,
You are right about the flywheel effect, and I am familiar with steam engines.
I spent 8 hours in a booth next to an ice cream vendor who used a steam engine to make ice cream. Made it a little harder to display motorcycles in a cloud of smoke, steam and noise!
My experience is that comparatively sized singles are more "torquey" and rideable at lower RPM's than mulit's. Just my experience.
My F650ST single felt much more rideable at low RPM's than my CB750K for example, but again, that's just my experience and impression, and rideability is subjective.
The definition of Torque, however, is not.
And if you double the force by having both pistons fire together on the same crank, you will, by definition, double the Torque.
The real world difference would have to be settled on a dyno.

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G-Man
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PostPosted: Sat Nov 28, 2009 2:40 pm    Post subject: Reply with quote

Brewsky

You are absolutely right about the torque - two pistons will make more instantaneous torque, but a dyno does not measure that. It measures an average value over some time base (say one second).

Otherwise the needle would be just dancing all over the place. So, my guess is that a big bang CB77 would show almost exactly the same torque on a dyno as a normal one. i.e you will only get two firing pulses per 720 degrees (2 revs) whichever way you spread them. If the gauge on the dyno could show peak torque - it will be higher for about 90 degrees of rotation but non-existent for a whole 630 degrees.

So you get the choice - twice the 'thump' for only 90 degrees or two normal thump for a total of 180 degrees (two separate firing strokes)

i.e 2xT x 90/720 or T x 180 / 720

G

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jensen
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Joined: 12 Feb 2008
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PostPosted: Sat Nov 28, 2009 3:47 pm    Post subject: Reply with quote

NO, there will be a difference in torque, not dramatically, but there will be.

I can explane it, but then I have to use physics, and formula's.
The last time I did (the oil debate) I was "gunned" down, a donkey doesn't hit one stone twice (dutch saying).

But think in the direction of mechanical losses, thermal losses, friction, and force resultants.

HINT :

You can start to describe all the forces from one cylinder in one complete cycle, recalculate for the loses then add up the other one both ways (zero degrees apart, 180 degrees apart and 360 degrees apart).

Describe the resultant torque vector in the total cycle over 720 degree's for both cylinders and you'll be surprised.

Jensen

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Last edited by jensen on Sun Nov 29, 2009 3:52 am; edited 1 time in total
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