Q: I see
advertisements for the joys and wisdom of driving a turbo-charged
How does the turbo
differ from a “regular” auto? Why would one choose a turbo over
some other engine? How do the purchase, operating and maintenance
A: Great questions,
Doug! Turbochargers boost engine power by around 25 percent on a
gasoline engine and about 40 percent on a diesel, allowing a
smaller, more efficient engine to be used in place of a larger one.
Instead of power being developed mainly at higher engine speeds, a
turbo flattens the torque curve, improving driveability and allowing
more efficient low-speed engine operation. Four cylinder
turbocharged engines are now generating 300+ horsepower, which
required a large V-8 in years past.
Engines need lots of
air and fuel to make power. Turbochargers pump air into an engine at
a higher rate than would occur if the engine draws it in naturally.
Driven by exhaust gasses, a turbine wheel rotates at as much as
200,000 RPM. At the opposite end of a connecting shaft, a compressor
wheel draws in fresh air and pumps it into the engine’s intake
manifold. A computer managed wastegate controls boost pressure to
safe levels, maximizing performance while preventing engine-damaging
detonation (an explosion, rather than a burn of combustion gasses).
An attractive feature
of turbochargers is they utilize otherwise wasted energy to operate,
rather than consuming it like a belt driven supercharger.
A slippery modern car
requires only about 20 horsepower to move down a level road at
highway speed. Additional power is required for acceleration and
hill climbing, which happens less frequently. A turbo matches this
behavior well as it loafs along until spooled up by higher throttle
opening and increased exhaust flow. This slight delay in operation
can be mitigated by the use of a small low-mass turbo, a combination
of two turbos, or a variable geometry turbo, which can adjust its
vanes to differing conditions.
The downside of a
turbocharged engine, compared to a naturally aspirated one, is
additional initial cost, a somewhat more congested engine
compartment, and a chance the turbo may not last the life of the
engine. Good maintenance is essential as the turbo’s very precise
bearings are lubricated with engine oil, which is subjected to
greater stress due to the turbo’s high temperature. Cooling system
maintenance, always important, helps insure proper cooling of the
turbo. Premium fuel is often required to prevent
pre-ignition/detonation, and a brief cool down or idling period
prior to shut-off doesn’t hurt, to baby the oil a bit.
After 160,000, miles
my Duramax is beginning to suffer from sticky turbo vanes, which
will require significant disassembly and cleaning, or possible turbo
replacement. Nonetheless, I’d have no concerns buying another
turbocharged vehicle, as the performance benefits outweigh potential
issues with this somewhat high-strung device.