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      09-28-2013, 07:39 AM   #88
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Originally Posted by mkoesel View Post
A rebuttal from out mystery scientist (in his theatre?)!

(I apologize for the rather unconventional chain of communications)
The formula given is a mechanical one. What is not shown is the combustion process and engine characteristics for different stroke lengths. It is these that also influence torque.

A tidbit to ponder over, is that in a petrol engine, the combustion process is over by around 14-16 degrees crank shaft angle ATDC. It is this critical stage that help the extra leverage at small crankshaft degrees make a significant difference in torque. The view is helped by the thought that no matter what force you apply to the top of a piston at TDC, the torque read at the crankshaft will be zero.


The main long stroke = higher torque basis is derived in part, in the commonly accepted view that long stroke engines produce peak torque at lower revs than a short stroke engine. They are simply more efficient in this range.

We also know that it is easier to produce higher torque figures at lower engine speeds.

For example, if we were to take a particular engine fitted with a medium cam profile and measure the torque, it would typically be higher than the same engine with a high duration camshaft. The high duration camshaft would develop the torque higher up in the rev scale, and the engine would physically produce more power, but peak torque would be lower (typically). (Of course a short stroke engine would favour building torque at higher revs, but the increase in torque would not be as significant)

Finally, on turbo charged engines, peak torque/power is limited to the onset of detonation. It is commonly understood that a wide flat disc (short stroke) is worse than a smaller higher disc (when talking about the shape of the squish area). This allows a long stroke engine to have more ignition advance, or more boost pressure for a given capacity. These two factors produce more torque in an engine.

The above is a general view, of course, there are exceptions.

Last edited by NISFAN; 09-28-2013 at 07:56 AM..