Re: AUDI & Mercedes

[Eliot Lim <eliot@u.washington.edu>]

On Tue, 24 Oct 1995 LToy@aol.com wrote:

> >>All I've ever driven are 2-valve per cylinder cars, but I've heard
> >>that multi-valve engines sacrifice low-rpm torque for high-rpm
> >>horsepower.
> >
> >You heard correctly - an Audi dealer told me this, and my `90 coupe
> >quattro (with the 20V head) seems to bear this out.  It behaves
> >somewhat like a turbo: lazy get up and go, but while the revs build
> >linearly, the g forces seem to build exponentially.
> 
> That tended to be true with the first "generation" of popular 4v/cylinder
> cars (early to mid 80s, i.e. VW 16v, very similar to Audi 20v) but some of
> the newer cars are pretty slick with their variable intake tracts, variable
> valve timing, and the like.  

the 20 valve non-turbo 5 is widely acknowledged to be not one of
audi's better efforts.  all the stereotyping of 4 valve heads apply.
however, look at the same engine with a turbo (and other refinements,
such as a lighter dual mass flywheel, direct ignition) as deployed on
the S4 to such devastating effect.  peaky?  yeah 1950 rpm max torque,
perfectly flat thru 4700 rpm and a 280 foot pounds 15 second overboost.
this engine is an engineer's dream.  

a vtec can rev to the blazes, but with only 110 lbft or so to play
with, it is largely a curiousity.  and thanks once again to a nice
cosy relationship to the media, this engine can produce acceleration
numbers not reproducible in real life.  not surprising.  a VR6
powered car or an eclipse turbo is much much quicker than a vtec.
yes, i have driven them all.  it's all about torque.

according to performance car, the current 4 valve head found in all
audis and VWs came from the 306bhp sport quattro.  the current gti
16V, not currently imported has a new head designed with more torque
in mind.  my guess is that the original 4 valve head design used in
the S1 was optimized for forced induction, which is why the S4 is such
a killer and the non-turbo versions pretty tame.


eliot