Turbo lag and supe lag

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

Diff'rent strokes for diff'rent folks maybe, but an important point about 
the new turbos needs to be made here. Lag is so minimal as to be irrelevant 
in real world driving. Inertia lag also affects mechanical superchargers 
and their boost curve is severely limited by their fixed rate of rev change.

Certainly, off the line there is no lag unless you don't know what you're 
doing. For a turbo you always get the revs up and the throttle open 
just  milliseconds before launch and the turbo is already there. Indeed, 
launching my 97 SAAB Aero is all about wheelspin control and nothing to do 
with the turbo, other than it can boost too hard too early and you end up 
sitting in a cloud of rubber smoke while you get smoked.... Rear drive or 
awd hard blowing turbos don't suffer too much from this fwd related issue.

One big advantage turbos have over other types of superchargers is you can 
get more boost without any increase in engine revs, if the engine needs 
more power but you don't need more speed in that gear. So for driving 
really fast over windy mountain roads a turbo can't be beat. As the engine 
loads up the turbo starts to pump harder due to the increased volume of 
exhaust gas. The turbo spools up but the engine doesn't need to. It really 
is like having two extra cylinders (or three extra if your turbo is on a 
V6). Turbo passing requires a tad more anticipation but lag is not the 
issue, rather any supercharged engine takes time to get that compressed air 
moving  into the engine, just as a normally aspirated engine needs a bit of 
a head start when standing on the loud pedal in high gear. I rarely shift 
down to pass in my turbo cars, just nail it and go. In fact, the Aero is so 
quick at highway speeds it is the first car I have to back off the gas when 
in the oncoming lane or I'm going just too fast. Previously, my philosophy 
was to minimize the time in the oncoming, lifting off only when safely back 
on my side of center. Do that in the Aero and you'll run out of cars to 
pass before you find space long enough to slot back in.

I think you'll find that most, if not all turbo supercharged engines are 
superior to mechanically supercharged engines for most, if not all 
applications. Except for the heat of course. Turbos and crowded engine 
compartments do not mix well. As a result turbos are not for the 
mechanically inept. Most premature turbo failures are due to improper 
running, too much boost too soon when cold, and not enough cool down time 
just before shutdown. Mechanical superchargers also get hot but they don't 
extract heat direct from the exhaust and pass it straight into the engine 
compartment like a turbo does. Turbos just don't wear out if properly 
handled, the only moving part that could wear, the turbine/compressor, 
doesn't touch anything so there's nothing to wear out until the seals fail 
or the bearings get toasted by coked oil bits. Wastegate wear is not an 
issue any more.

Maybe Alfa should bring over a turbo?






Michael Smith
Calgary, Alberta,Canada
91 Alfa 164L
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