[s-cars] New 5 cylinder vs. AAN
chapel976 at gmail.com
Fri Oct 15 05:48:32 PDT 2010
and this is why rotaries are better than reciprocating engines :D
On Fri, Oct 15, 2010 at 6:46 AM, John Cody Forbes <cody at 5000tq.com> wrote:
> Yeah it's all down to piston acceleration and crank offsets.
> On a long stroke engine one of the main reasons you get more torque is the
> increased leverage on the crank shaft. Think of it like using a longer
> ratchet to tighten a bolt. You are able to generate about the same force
> yourself, but via the longer ratchet handle you apply more torque to the
> bolt. In a long stroke engine the explosion of the air/fuel mixture is going
> to generate basically the same force as it would in a shorter stroke engine,
> but the increased offset of the rod journal vs. the crank centerline applies
> more torque.
> Sounds great right? There's a caveat. At a given RPM figure any piston in
> any engine has to travel the distance of the stroke in the exact same amount
> of time. On a long stroke engine what this means is that the piston must
> travel faster to cover the greater distance in the same time. Remember that
> on every stroke the piston must accelerate from a stop, reach a maximum
> speed, then stop again and get forced in the other direction. If you speed
> up it's velocity you are increasing the amount of inertia and at some point
> the inertia becomes too great and, for instance, the connecting rod breaks
> in half when trying to stop the piston from meeting the cylinder head. More
> commonly the force of the rod trying to stop the piston becomes great enough
> to force the oil film between the crank and rod bearing out and the rod
> bearing contacts the crankshaft resulting in wear. In the real world the
> maximum average speed of a piston is about 25 meters per second. This means
> a theoretical engine with a stroke of 100mm must not exceed about 7500rpm.
> If the stroke were 75mm the engine could do about 10,000rpm before piston
> speeds become too great. Of course many other factors are involved (weight
> of the piston, weight of the connecting rod, and the ability to flow enough
> air to make it worthwhile), but that's the gist of it.
> -Cody (mobile)
> On Oct 14, 2010, at 11:29 PM, "JC" <jc at j2c3.com> wrote:
> > By Jove I think he's got it! (nohomo)
> > Think Harleys and Muricun V8's.
> >> And on that note,
> >> One would expect a higher torque generated from a longer
> >> stroke cylinder.
> >> Correct ?
> >> On 2010-10-14, at 7:19 PM, JC wrote:
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