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

M Pederson mlped at qwest.net
Thu Feb 5 11:15:03 EST 2004

```Yep, put the Excel spreadsheet parenthesis in the wrong place.  Thanks Paul,
with the correction I get all your numbers with the exception of #1 which I

Looks like, at least in "stock" trim Audi too is observing Victory's 100,000
ft/sec^2 RROT (rough rule of thumb) suggested piston acceleration limits.

I wonder how significant this is in the ring land failures I've heard of
with a few of the stroker pistons.  Looks like even keeping with the 150mm
rod's 1.571 rod ratio doesn't get you close, and for the hi-po optimists in
the builder group, 8,000 rpm takes one to:

8000 rpm @ 144/86.4mm -> 1.667 ~> 129,288 ft/sec^2
8000 rpm @ 144/95.5mm -> 1.508 ~> 146,378 ft/sec^2
8000 rpm @ 150/95.5mm -> 1.571 ~> 144,920 ft/sec^2

7000 rpm @ 156/95.5mm -> 1.570 ~> 110,995
7000 rpm @ 144/92.8mm ~> 1.616 ~> 107,102 ft/sec^2

Mike

> -----Original Message-----
> From: Paul Gailus [mailto:gailus at mindspring.com]

>
> Interesting site, Mike.
>
> I think you may not have divided by the factor 2n
> as needed in the formula:
> Z = (N**2) S (1+ 1/(2n) ) / 2189
>
> Instead, I think you left the "n" on top as in:
> Z = (N**2) S (1+ (1/2)n ) / 2189
>
> Using the first formula you get:
>
> 7000 rpm @ 144/86.4mm -> 1.667 ~> 109,400 ft/sec^2 ~> 98,986
> 7000 rpm @ 144/95.5mm -> 1.508 ~> 112,100 ft/sec^2
> 7000 rpm @ 150/95.5mm -> 1.571 ~> 111,000 ft/sec^2
>
> Note that (111,000 ft/sec^2) / ((32ft/sec^2)/g)  = 3470 g's
> of acceleration.
>
> Paul
>
>
> ----- Original Message -----
> From: mlp qwest <mlped at qwest.net>

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