Ray,
Thanks for this interesting post. As an experimental physicist, I also
strongly believe in "real world" confirmation of theory. Nothing pleases an
experimentalist more than disproving a widely accepted theory. Of course,
then the challenge is to develop the correct theory. However, in the case
at hand I have seen neither data nor any convincing theory to explain
higher output from longer rods. And, as you say, "even turbine engines,
produced to far closer specs than auto engines, do not make the same power
at birth...they have to be "adjusted" to a set standard." So, simply
comparing two engines nominally equal except for rod length would not be
enough to establish a solid case. And, if fact, it is impossible to just
change rod length without making other changes, like relocating the wrist
pin. On the other hand there is a good theoretical foundation for the
benefit of longer rods in terms of reducing stress, and this alone would
justify their use in high rpm motors.
I understand that at least some of the newer motors being built have quite
high rod length to stroke ratios; e.g., the Ford 4.6L modular motor. I'm
willing to bet there are at least one or two engineers at Ford that could
tell us quite a story on this subject. Unfortunately, they may consider
this to be "proprietary" information and, therefore, be unwilling to
divulge it to the masses. What a pity. It would be nice to know the
reason(s) for this recent trend toward longer rods. Let us know if you hear
any good stories in this regard.
Still curious,
Bob
At 10:18 PM 10/4/98 -0500, Ray McCrary wrote:
>Well, Guys,
>
>I don't pretend to play an engineer on TV, but I know that the SVO pistons
>have a relocated pin in them that means that you have to use a longer rod.
>
>I know that ALL of the major Ford engine builders (including Ford
>Motorsports) that I contacted used the longer rods and claimed PRACTICAL
>horsepower and reliability gains by doing so.
>
>I remember the discussion you refer to; I was party to it, and after
>reading MANY postings by a great many people who seemed to know something
>that I didn't, I gave up and began to contact people with ACTUAL experience
>in making reliable horsepower.
>
>I suspect that the math majors are leaving some variable out of their
>calculations....either that or the dynos are wrong, and a lot of people who
>work at Ford are wrong.
>
>I doubt that "convenience" of production has much to do with the production
>of special components for all out race engines.
>
>As to "matched" engines, let me say that even turbine engines, produced to
>far closer specs than auto engines, do not make the same power at
>birth...they have to be "adjusted" to a set standard.
>
>In short, theory is interesting, but I'll take real world knowledge anytime!
>
>Regards,
>Ray
>
Robert L. Palmer
Dept. of AMES, Univ. of Calif., San Diego
rpalmer@ames.ucsd.edu
rpalmer@cts.com
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