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
At 08:13 PM 9/29/98 -0700, Bob Palmer wrote:
>Barry,
>
>You may or may not be aware that about a year ago we had quite a lengthy
>(no pun intended) discussion on this subject on the Tiger List. Although no
>official winner was declared, contributions by Dr. Mayfield and others gave
>strong theoretical support for the conclusion that rod length to stroke
>ratio was not a significant factor in engine output, either torque or
>horsepower. For one thing, if the torque is integrated over the full
>revolution, the answer is independent of the length/stroke ratio. Also, the
>experimental evidence is that similar results are obtained from various
>motors that cover an extremely wide range of length/stroke ratios. One
>point I believe I made early on in the discussion was that there was an
>optimum length/stroke ratio in terms of minimizing the stress on the rod. I
>believe, if memory serves me, this minimum occurs at length/stroke = 1.73 .
>For a 3.5" stroke, this would make the optimum rod length very close to the
>6" you now use. However, the basis for calculating this optimum length has
>nothing to do with power or efficiency; only minimizing the rod stress
>which, of course, does become very important at high rpms. I have never
>heard anyone explain why the Boss 302 used the longer 289 basic HiPo rod,
>but I suspect it was just easier than producing a special shorter heavy
>duty 302 rod rather than any esoteric reasons having to do with output,
>high rpm or otherwise. Alternatively, they may have been trying to reduce
>the stress on the rod at high rpms by using a rod closer to the optimum
>ratio. We may never know for sure.
>
>My question for you, Barry, is what, if any, explanation can you give for
>the better high rpm output which you seem to attribute solely to the longer
>rod length? Were there any other differences between the two motors you are
>comparing other than rod length which might account for the differences?
>Being a skeptic, I would say that it is probably harder to build two
>engines with identical output than to build two that are the same. Slight
>differences in porting, port alignment, chamber volume, etc., etc., all add
>up to give a different result. I think I can prove to you that the
>difference in friction between the 5.4" and 6" rods is inconsequential
>compared to the 400 or so horspower you are producing. Also, the longer rod
>VERY slightly extends the time the piston spends near TDC, but again, this
>seems too small and effect to be important, although several car magazine
>articles on this subject have made a big deal out of extending the dwell
>near TDC.
>
>Now the plot thickens with this latest post:
>
>>Ray (or Barry or anyone else with an opinion),
>>
>>
>>Any comment on the trick where you reverse the pistons to relocate the
>wrist pin
>>and thus improve the rod geometry?
>>
>>
>>Regards,
>>
>>
>>Theo Smit
>>tsmit@novatel.ca
>>B382002705
>>
>I first heard about reversing the direction of the pistons in talking to
>some MOPAR people. Whether this trick actually works, again I'm skeptical,
>but it is believed by a number of the MOPAR crowd. For those that are a
>little confused by what is being done here, you have to understand that
>there are basically two types of pistons;symmetric tops and asymmetric
>tops. Most, if not all, pop-up pistons have asymmetric tops to clear the
>valves. This means that the ones on the left side are facing the opposite
>way as the ones on the right. Consequently, unless you make special pistons
>for the right and left banks, the wirst pins on these pistons have to be
>centered on the piston. Flat top pistons, on the other hand, have symmetric
>fly cuts and can be installed either way; EXCEPT that in this case, they
>are made with the wrist pin off-center. The reason for this is just to
>quite them down so they don't slap so hard against the side of the cylinder
>as they reverse direction. Again, this has nothing at all to do with power,
>just makes the pistons a little quieter (mostly when idling). Getting back
>to Theo's question, for reversing the pistons to possibly have any effect,
>you would necessarily have to be using flat top pistons with asymmetric
>wrist pins. Then the question is, would this really make any difference in
>torque/power output. Again, I think not based on the fact that the
>integrated torque over the whole revolution is, I believe, still the same.
>
>The problem with these kind of anecdotal stories is they are much easier to
>get started than they are to refute. Emotionally, we all want to believe in
>magic bullets, quick fixes, and engine builder's secrets. The truth is
>usually much less exciting. However, I do have a reasonably open mind to
>anyone's suggestions as to how we could account for improvements in output
>from just changing the rod length/stroke ratio or similar modifications.
>Barry??
>
>Skeptical in San Diego,
>
>Bob
>
>
>At 08:23 PM 9/29/98 -0500, Ray McCrary wrote:
>>>Return-Path: <bkschonb.ucs@smtp.usi.edu>
>>>Date: Tue, 29 Sep 1998 14:20:32 -0400
>>>From: "Schonberger, Barry" <bkschonb.ucs@smtp.usi.edu>
>>>Sender: "Schonberger, Barry" <bkschonb.ucs@smtp.usi.edu>
>>>Organization: University of Southern Indiana
>>>To: spook01@mindspring.com (Ray McCrary)
>>>Subject: Re: Rod length and oil additives
>>>Importance: Normal
>>>
>>>Ray, the standard on our race engines for Team Tiger was 5.4" it is now
>>>6". High RPM horsepower is significantly increased.
>>>
>>>
>>>Barry Kent Schonberger
>>>Dean of Students
>>>University of Southern Indiana
>>>8600 University Blvd.
>>>Evansville, IN 47712
>>>(812) 464-1862
>>>(812) 465-7021 FAX
>>>BKSCHONB.UCS@SMTP.USI.EDU
>>>
>>>
>>
>Robert L. Palmer
>Dept. of AMES, Univ. of Calif., San Diego
>rpalmer@ames.ucsd.edu
>rpalmer@cts.com
>
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