# [Audi20V_Kruemmer] RE: [s-cars] Question about compression ratios and tuning - More 20vt

mlp qwest mlped at qwest.net
Wed Feb 4 11:57:04 EST 2004

```A couple of other sites of varying sophistication dealing directly or
tangentialy with the matter:

http://victorylibrary.com/mopar/cam-tech-c.htm is a site I originally came
across in looking for better information on the effects of connecting rod
ratios in the "stroker" motor.

Going back to a previous thread on piston speed, the victorylibrary has some
interesting material on the effects of long vs. short rod on piston speed
vs. maximum accelerations.

7000 rpm @ 144/86.4mm -> 1.667 ~> 139,595 ft/sec^2
7000 rpm @ 144/95.5mm -> 1.508 ~> 147,615 ft/sec^2
7000 rpm @ 150/95.5mm -> 1.571 ~> 150,259 ft/sec^2

But I suspect something is wrong with my math, or interpretation of Victory
Library's formula, if I assume the longer rod ratio in example #3 with the
Eurovan 150mm c-to-c rods ought to have returned an acceleration less than
the that of the 144/95.5mm rod combination.  In any case, all the values
apear to be well above Victory Libraries suggested "100,000 ft/sec^2"  Gotta
love those motorcycle guys  :-)

Also there's  http://www.mix-net.net/~red/uccr.html  -

Mike

~-----Original Message-----
~From: Alex Neckas [mailto:aneckas at comcast.net]
~Sent: Tuesday, February 03, 2004 11:41 AM

~
~
~http://toyotaperformance.com/pushing.htm
~
~Some good info, some ??? info.  You may want to take the
~time to review the "foundation" articles (at the top).
~
~Regards,
~Alex Neckas
~
~M Pederson wrote:
~>
~> For tuning purposes, isn't your static CR some what
~> irrelevant?
~> You are going to be more affected by the dynamic
~> compression ratio's which
~> as I understand, are substantially affected by cam
~> profiles (granted this is
~> probably a pretty fixed constant in most of the motors you
~> will see) and
~> volumetric efficiency which while one might assume would
~> be fairly constant
~> and consistent from factory conditioned motor to motor,
~> might begin to vary
~> more than a little in motors with rebuilt heads and valve
~> jobs of varying
~> skill and quality.
~>
~> On a running motor, it sounds to me like you would be
~> tuning for optimal
~> timing based on the motors dynamic, not static compression
~> ratio.
~>
~> Mike
~>
~> > -----Original Message-----
~> > From: Mihnea Cotet [mailto:mik at info.fundp.ac.be]
~> >
~> > Nope, ADU is 9:1, I can't remember where I've read it
~> but I'm sure it has.
~> > My previous example of an ABY running everything ADU
~> > gasket and having to run a few degrees less timing
~> > self-speaking, I've BTDT several times, on ABYs and
~> AANs.
~> >
~> > HTH,
~> >
~> > Mihnea
~>
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```