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What causes exhaust snap, crackle and pop?

Geoff Fear, Hyundai’s official N tech explains to the CarAdvice podcast panel

You’ve probably heard it before: that pop and crackle in the exhaust note of a performance car. A number of manufacturers produce cars with bi-modal exhausts allowing the driver to select what kind of noise they’d like their car to produce, and often the louder, sportier noise includes an armada of racy cracks on the overrun.

Speaking on the CarAdvice podcast, Hyundai’s official N technician from N Performance Australia, Geoff Fear, explained how the exhaust crackle was created for the Hyundai i30 N.

“What we’ve done with the N is played with the cam timing, ignition timing, and the volume of fuel. So normally when you get off the throttle, you turn off the fuel and revs come down,” he told the podcast panel.

“So what we’ve done is tuned it to give a little extra fuel at that point, advance the exhaust cam timing so that the flame actually comes out of the exhaust, pops out past the valves, and retard the ignition timing to start the flame later so what it actually does is create a jet in the exhaust manifold.”