How engine turbochargers really work

.

A cutaway view of a typical turbocharger, showing the turbine, in red, which is spun up by the hot gases flowing down the exhaust pipe, and the impeller, in blue, which forces the incoming charge into the cylinder under pressure, regulated by the gold-coloured wastegate on the far left.

Ever since man began to chase women, or flee from them, he has sought ways to increase his speed.

Horses worked well enough, but even they needed persuasion in the shape of whips and spurs. Then the dreaded motor car entered the scene and the quest for higher performance continued.

So we threw away our spurs and headed for larger capacity engines or gave the engines an extra boost by way of the supercharger or turbocharger. The difference between the two is the method used to drive the compressor, commonly called the blower.

While the supercharger blower is driven mechanically, the turbocharger relies on the velocity of the exhaust gases. The effectiveness of the system remains regardless of altitude and many cars with turbochargers and smaller engines give the performance of larger engined vehicles, yet retain their fuel economy during normal operation.

OK, I’ll get to the point.

Like many things, turbochargers have certain characteristics which could alarm somebody who is unfamiliar with them. As they operate at very high revs, there is often an audible whine. Normally this is nothing to worry about, but if it really troubles you, get the thing checked to be on the safe side.

The case I have in mind was the reverse situation; the new owner was worried because there was no whine and drew the conclusion that the turbocharger was not working. He said the car was fast, but as his previous car was a diesel, it would naturally seem faster. The best way to determine if a turbocharger is doing its job is to connect a boost gauge to the inlet manifold.

Some cars have such things as standard fittings.

If this is not so, then seek a tuning agency for advice on buying and fitting a boost gauge before attempting a DIY exercise. A professional should be able to tell you the risks involved and the probable performance boost. The engine must be in first class condition to accept safely the additional stresses of performance boosting.

Also, ask your insurance broker how much extra premium you will be expected to pay if you carry out the modification.

Naturally, with operating speeds of perhaps up to 130 000 rpm, adequate oil pressure is taken care of by the engine’s lubrication system. It used to be recommended on some engines that the engine be allowed to idle for a while before switching off the engine when turbine speed remained high and was no longer being fed by engine oil pressure.

EXTRA COST

There is a wastegate that causes exhaust gases to bypass the turbo when a predetermined manifold pressure is attained. This is necessary because excessive turbocharging may cause detonation and with it engine damage. A spring-loaded diaphragm sensitive to inlet manifold pressure regulates the wastegate.

A detonation sensor in the thermostat housing (or a manifold pressure sensor) sends a signal to the spark control unit to retard ignition timing if detonation threatens.

I would say that cars with turbochargers fitted as original equipment are very worthwhile, but would hesitate to recommend the DIY route. The extra performance might be thrilling, but one way or another it will cost you extra cash. - Star Motoring

Motoring newsletter - click here to keep up to speed with the best in motoring