Turbo Lover: Test Your Exhaust-Driven Forced-Induction IQ

Illustration for article titled Turbo Lover: Test Your Exhaust-Driven Forced-Induction IQ

For the engineers out there, this should be a snap. For the Honeywell employees, it should be even easier. Interestingly, we found this quiz because we've lately become re-obsessed with Richmond, VA's Avail, who once sung about Kepone in the James River. Said pesticide was supplied by Alllied Chemical, who merged with Signal Oil to become Allied-Signal and later AlliedSignal, which then merged with Honeywell. So yeah, punk rock to water pollution to turbochargers. Never let it be said that our ADD never gave a reason to widdle on the clock. Oh, and don't feed Prestone to your pets. Really. Don't.

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Turbo I.Q. Test [Honeywell]

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Honeywell got one of its own questions wrong!

Question 10 on the Turbo IQ test asks,

"A variable geometry turbo such as Garrett®VNT™? (Variable Nozzle Turbine) turbo delivers better performance than a Wastegate turbo by:

A. Providing rapid movement of the vanes.

B. Making the turbocharger more complex.

C. Using moveable vanes to control the amount of air supplied to the engine.

D. Providing increased boost at low engine speed only."

According to Honeywell, the correct answer is C, "Using moveable vanes to control the amount of air supplied to the engine." In fact, the vanes control the flow of exhaust to the turbo, not intake to the engine.

A turbo has an optimal range of exhaust pressure. If exhaust pressure is too low, the turbo won't provide any compression; if exhaust pressure is too high, it will blow the turbo, the engine, or both.

Early turbos solved the problem of overboost by using a turbine large and/or heavy enough so that engine exhaust just couldn't turn the turbine fast enough to generate overboost. But at low speeds these turbos did squat, and hence the infamous turbo lag.

A wastegate is a safety valve—it blows before the turbo can generate enough intake pressure to blow the engine. Since the turbo can't blow itself up, it is safe to use a lighter turbine that will be actuated at lower revs. However, at higher speeds, with the wastegate open, the turbo no longer does any good. So in essence, a wastegate trades no performance at low revs for no performance at high revs.

Moveable vanes gradually increase the turbo's bypass ratio, sending less exhaust into the turbine and more straight out through the exhaust.

Like wastegates, moveable vanes eliminate the problem of overboost, allowing the use of a lighter turbine that will work at lower revs. Unlike wastegates, moveable vanes still allow the turbo to contribute to performance at higher revs. True, the vanes let more of the exhaust escape at higher revs, but since there's more pressure to begin with at higher revs, the turbo still works.