Date: Thu, 30 Nov 1995 21:12:58 -0800 (PST)
From: Greg Meboe <meboe@wsunix.wsu.edu>
Subject: Re: Stroking...
I told myself I'd stay out of this one. Oh well, I'll try to limit
myself anyway.
On Thu, 30 Nov 1995, Philip Barnes wrote:
> Tom:
> Dreher states that the intake charge velocity is higher in a long stroke
> motor. For equivalent engine speeds, ie. crankshaft rotational velocity,
> an engine with a long stroke (larger crank throw/diameter) will have
> higher piston speeds in the middle of the stroke.
No argument here.
> This increased piston velocity also causes the rate of change in cylinder
> pressure to be much higher.
Where did this come from? The change in Volume of the cylinder is what
causes the cylinder to be filled, and the change in volume during filling is
the same for cylinders of similar displacement, regardless of piston
diameter or stroke.
> To take advantage of this condition, intake
> plumbing should be less restrictive to give better low RPM flow.
But that would lead us to reason that long stroke engines would benefit
more from 4 valves per cylinder than short stroke engines, yet engine
manufacturers do exactly the opposite.
> This over-simplifies the problem, because every engine design has an
> optimum set of conditions for peak output.
Right you are. Engine design is a very complicated issue.
Greg
Greg Meboe meboe@lestat.scs.wsu.edu
Web site>> http://www.scs.wsu.edu/~meboe
Dept. of Mechanical and Materials Engineering
Washington State University, Pullman, Wa.
'85 XJ-12 H.E. (daily) '67 Spit-6 '74 TR-6
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