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Re: S4 20v vs S2 10v
> >my understanding is that the 9.3 compression on the S4 is for
> >off-boost response.. once the turbo spools up, CR is really quite a
> >meaningless number, because 2 bars of boost is 2 bars of boost,
> >regardless of what the geometric dimensions of the engine are. i.e. 2
> >bars in a 9.3 compression engine is equally likely to detonate as 2
> >bars in a 7.8 engine, all other things being equal.. no?
> NO !!
> Boost pressure is at the intake manifold. The engine then FURTHER
> compreses it according to the compression ratio. Therefore high boost
> + high compression => higher likelihood of detonation.
i stand corrected. so, the high compression would be good for off-boost
response (claims audi) and also higher efficiency (better fuel mileage).
any other advantages? seems to me that a lower CR is better for
high boost and high outputs. is that correct?