The pause before turbocharger kicks in

By Doug McAllister

Q. I often read the term "turbo lag" in auto reviews or columns in the Daily Herald. The term is used in reference to turbocharged engines. In layman's language, what is the reason for the turbo lag when I put my foot on the gas pedal?

- William, Oakbrook Terrace

A. Hi William and thanks for your question.

A turbocharger is a basically a compressor that puts the engine's air intake under pressure, causing an effective rise in engine compression by packing more air and fuel into the combustion chamber.

There are two types of compressors used: a supercharger, which is typically belt driven; and a turbocharger, which is driven by the engine's own exhaust. With the turbocharger, there are two impellers that spin to compress air; one side is driven by the exhaust and the other side compresses the air.

The lag comes in when the turbo takes a second to start spinning fast enough off the exhaust stream to start compressing the air intake. This all happens pretty fast when you press down on the accelerator pedal. However, most of the time there is still a noticeable lag of a second or two while the turbo spools up, whereas a supercharger spools up instantly.

After this brief "turbo lag," or pause, a driver can feel more power and noticeable speed from the engine.

I hope this answers your question.

• Douglas Automotive is at 417 W. Main St., Barrington; 123 Virginia Road, Crystal Lake; and 416 Northwest Hwy., Fox River Grove. For information, visit douglasautomotive.com. Send questions to underthehood@dailyherald.com.