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big vs small turbos.....
On the issue of big vs small turbos, a relevant quote from
an article in the Sept. '93 _European Car_ magazine on the
Cosworth Escort GT AWD Pro Rally car;
".....Turbo lag is the lasting impression of the engine.
For homologation reasons, Ford has fitted the biggest turbo
they could get away with on a production road car. After
the first 2500 (required for homologation, Ed.) cars are
built, however, they will revert to a smaller turbo
unit..... The cars built from then on should have plenty
of down-low flexibility....."
Audi faced the very same issues with the Ur Quattro, fully
intending to homologate the automobile for Pro Rally use
back in the very early 1980s, only Audi never reverted to
a more sensibly sized turbo for street use after
homologation was completed, till the advent of the S4 and
20 valve engines.
I guess the S4 was never intended for rally or homologation
use so fitting the largest possible turbo wasn't an issue,
they could fit a smaller K24 unit and optimise the setup for
real-world over-the-road performance.