Variable Inlet Tracts

[Keith Walker <100662.3423@domain.elided>]

>>Of course the ultimate for street engines is variable intake, and now
exhaust, tracts. <<

Worth pointing out that Alfa are using variable length inlet tracts on th=
e
latest version of the 16V Twin Spark engine. I don't know it this is a
true variable length or whether it is just a pair of inlet tracts which c=
an
be switched between (a system used some time ago on the Fiat Croma).

For variable exhaust tracts I do not know of any. Yamaha use a crude
system called EXUP (EXhaust Ulitmate Power or some such nonesense).
The aim of this is to allow the engine to cope with an exhaust optimised
for high revs without causing very poor running at half peak power (the
point where the exhaust preasure waves do their worst and push the
exhaust gases back into the engine). Essentially it is a servo operated
valve in the exhaust which is either open (exhaust working properly) or
partially closed to screw up the preasure waves and prevent them
causing problems at low revs.

This system has been in use on road bikes for about a decade now, and
the main downside is just a large increase in the sales of Copaslip.

All the best

Keith

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