And with all that said ........... Mr Wankel came along with a different
problem, how to keep the Rs below 8000.

Stan Wilder

On Tue, 19 Feb 2002 21:45:22 EST Frank Grunthaner <FrankGRUN@AOL.COM>
writes:
> In a message dated 2/19/02 10:47:45 AM, al_knoll@PACBELL.NET writes:
>
> << Donning my Nomex...
>
>
> I seem to recall that engine wear is proportional to piston feet per
> mile.
>
> How far a piston travels in moving the car one mile.
>
>
> Given same lubricants, operating temperatures, the motor with more
> p-ft/mi
>
> will wear out sooner.
>
>
> Of course there are many other elements in the wear equation too but
> P-F/mi
>
> seemed important enough to "Rod and Truck" to include as a parameter
> on
>
> their road tests. >>
>
> Al,
>
> True as far as it goes. More details in a long soliloquy I put in
> the
> archives about a year ago on piston speeds. To summarize, the
> current
> materials set (post 1980 for VW/Audi) allows the choice of wall
> finishes,
> materials, ring surfaces and compositions such that continual
> operation at
> 5000 rpm with high loads (1 HP per cubic inch) will give a 75% wear
> point in
> 300,000 km. This is in contrast with a 75% wear point on a 1985 Ford
> V8 at
> 80,000 miles. The point is that the engineer designs for a
> load-wear-life p
> rofile. Now it is true that you can reduce the piston ring wear for
> the same
> engine by 20% by operating it at 4000 rpm vs. 5000. But not the
> whole story.
>
> The thermal transmission from friction and conduction is also a
> strong
> function rpm, load, etc., etc. But this curve is the locus of a
> multi
> dimensional plot in which there are real optimal values. Here the
> engineers
> (plural) set some finely tuned use parameters because this effects
> the
> thermal efficiency of the heat engine. These and other changes like
> cam
> timing, valve lift, chamber turbulence, intake runner length,
> exhaust gas
> pressure phasing, etc. all combine for optimal operating points.
>
> So a slugmobile (Ford Expedition) is tuned for maximum fuel
> efficiency
> (oxymoron, sorry) at 1700 rpm and probably gets 0.1 mpg more here
> than at
> 2000. The optimal operating point for the waterboxers and the inline
> 4's is
> given in the brake specific power per unit fuel flow curves in the
> various VW
> design papers I have posted on Alistair Bell's web site. For any
> car, max
> fuel economy and maximum life will coincide (per unit work done).
> This
> requires operation at that rpm, full throttle and gearing for
> maximum load.
> For any given engine rpm and extraction load, there is a consumption
> graph
> (Alistair doesn't have it posted yet)  that shows how much excess
> fuel you
> need to use to move a load at the non optimal values. Varies by 50%
> over the
> whole operating space.
>
> Oh well, if the engine is designed for high rpm run at high rpm. The
> loss in
> engine life compared to lower rpm running will be unmeasurable. Car
> goes for
> 200000 miles, or 250000 I still will have my money out of the
> conveyance.
>
> BTW, as near as I can tell no similar data charts have ever been
> published by
> Fuji Heavy Industries. I can only conclude that they are shamed by
> the
> comparison with other competitive technologies!
>
> Frank Grunthaner
>
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