Turbos and tickets

[C M Smith <cmsmith@domain.elided>]

Turbos are not completely free of course. They do take advantage of the 
remaining expansion potential of exhaust gas just as it leaves the exhaust 
port, but the resulting resistance provided by the turbine does increase 
exhaust back pressure somewhat. Turbos run well with low valve overlap 
partly because exhaust extraction and intake ramming do not work well if 
there's a turbine in the exhaust tract and a compressor in the intake. Some 
of the back pressure loss is regained on a street engine by the reduction 
in the need for exhaust muffling. the turbine does an excellent job of 
breaking up the exhaust pulses allowing for a fairly free flow exhaust to 
be fitted, without sacrificing noise levels. Turbos remind me of 
compounding in steam engines in that wasted expansion energy is captured 
and converted to work. Low pressure turbos are particularly efficient. Next 
up in efficiency are the SAAB type of automotive turbos which boost at very 
high levels (nearly 1 Bar) at very low rpm and rapidly taper off towards 
redline, producing stump pulling torque for impressive acceleration while 
preserving engine longevity, fuel economy, and fairly good top end ( a 2.0 
litre high pressure turbo SAAB will easily run to 140 mph).

As for the old "my speedo wasn't accurate " defence you will of course 
realize that you need to be reasonably ignorant of this problem before it 
can constitute a defence at law. In our local jurisdiction this defence is 
notorious due to the fact that a police court judge used it successfully! 
His defence relied on the twin facts of ignorance that his speedo was 
inaccurate and reasonableness in not realizing that it needed to be 
checked. He was acquitted of doing 10 mph over the limit on this ground. If 
he'd been doing 20 mph over it would have been too obvious that his speedo 
was inaccurate so the defence wouldn't work. His car at the time? An Alfa 
GT of course.

Cheers


Michael Smith
Calgary, Alberta,Canada
91 Alfa 164L
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