Horse Power and its Effectiveness

[Shannen Durphey]

John_Calabrese at ENGELHARD.COM wrote:
> 
> Please respond to gmecm at efi332.eng.ohio-state.edu
> 
> To:   gmecm at efi332.eng.ohio-state.edu
> cc:    (bcc: John Calabrese/ETG/ENGELHARD)
> Subject:  Re: Horse Power and its Effectiveness
> 
> >For a given displacement, long stroke means small bore means less force.
> >This exactly balances out the longer moment arm.  Long stroke motors have a
> >harder time at high revs (due to both inertia and limited breathing) but
> >they offer no advantage in low speed torque.
> 
> Small bore doesn't mean less force.  You are still releasing the same amount of
> energy in combustion. 
The amount of air and fuel drawn in is variable between engines, so
combustion pressure is also variable.

> You have just concentrated it over a smaller piston area.
Let's say the combustion pressure is the same.  Seems to me that the
smaller piston means less force, just like in a hydraulic system.

> How cou;d a stroker suffer from limited brreathing, if it is a "given
> displacement"?  Wouldn't the other motor suffer as well??

I think rod ratio is more the key than stroke.  If the piston stays
near BDC longer, there's more time for the intake charge to fill the
cylinder.  Similar with exhaust stroke at TDC.   Shorter strokes with
the same rod length allow piston to dwell longer near the ends of
their travel.  Also has to do with piston speeds, so I've read, but it
really seems like piston dwell times play the larger role in breathing
as any open cylinder will "fill up" completely if given enough time,
no matter how quickly it's volume is increased.
'Course this is just random muttering from me, and getting away from
GMECM too.
Shannen