Re: audi 4 valve heads

["Karl Nordstrom" <KXN2@PSUVM.PSU.EDU>]

I wrote:
>eliot@lanmola.engr.washington.edu (eliot) writes:

>> ...the 89 (?) model onwards got the 20 valve head and the sophisticated
>>boost control.  You know that "max. torque at 1950 rpm" engine.

>How do they do that?

>From Car & Driver's Technical Highlights column of an unknown month:

Audi's revamped 200 line sports a twenty-valve version of the turbocharged 2.2
liter in-line five.  The new aluminum head houses twin cams...  Hydraulic
lifters are standard.  A 9.3:1 compression ratio, unusually high for a
turbocharged engine, improves off-boost output.

Further reducing turbo lag is an intake system that benefits heavily from
Audi's racing experience.  The intake tract is fitted with a mechanical bypass
valve that reacts to intake-manifold pressure.  It is opened by vacuum whenever
the throttle plate closed (such as during deceleration of idle), allowing
intake air to reciculate through the turgocharger--which spins but doesn't
generate boost.  This helps keep turbine speed up and cuts turbocharger
response time whenever the throttle is opened again.  The watercolled KKK K24
turbocharger supplies up to 12.0 psi of boost as low as 1950 rpm.  The pressure
is regulated by a Bosch Motronic electonic engine-control system through a
waste-gate-pressure control valve.  This electronic boost management keeps the
torque almost constant between 1950 and 4500 rpm.  Other combustion control
pieces include a hotwire mass-air sensor, dual knock sensors, and port fuel
injection.  The new turbo five puts out 217 hp at 5700 and a healthy 228
pound-feet of torque at a very low 1950 rpm.