Demystifying the world of turbos
What is a ‘‘turbo’’ engine, and why is it better? Brad Bergholdt sheds some light on an often confusing subject.
Q I see ads for the joys and wisdom of driving a turbocharged car. How does the turbo differ from a ‘‘regular’’ car? Why would one choose a turbo over some other engine? How do the purchase, operating and maintenance costs differ? — Doug
A
Great questions, Doug! Turbochargers boost engine power by around 25% on a petrol engine and about 40% 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 lowspeed engine operation. Fourcylinder turbocharged engines are now generating 300+ horsepower (224kW), which previously required a large V8 engine.
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 200,000rpm. 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, maximising performance while preventing engine-damaging detonation (an explosion, rather than a burn of combustion gasses).
An attractive feature of turbochargers is they utilise otherwise wasted energy to operate, rather than consuming it like a beltdriven supercharger.
A slippery modern car requires only about 20hp (15kW) 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 behaviour 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 lowmass 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 naturallyaspirated 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 preignition/ detonation, and a brief cool down or idling period prior to shutoff doesn’t hurt, to baby the oil a bit.
After 250,000km my Duramax V8 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 highstrung device. — TCA