[combustion]

Originally Posted by edmunds.com

Of the three trucks we tested on the dyno, only the Silverado produced inconsistent results that appeared curiously low across nearly the entire rev range. Most unexpected was a power spike just before redline.

Although the spike resulted in a peak of 297 hp at the wheels — about right for the rated 367 hp at the flywheel, once drivetrain loss is factored in — the Silverado's measured power appeared to be underachieving everywhere else in the rev range.

In fact, the Chevy produces significantly less power than the Titan for the duration of the dyno test until the Chevy finally surpasses the Titan's peak of 291 hp at the wheels.

As it turns out, the explanation boils down to an engine calibration strategy. GM calibrated the 367-hp 6.0-liter V8 to remain in stoichiometric "closed-loop" fuel delivery mode for 4 seconds after the throttle is floored. This fueling strategy helps keep emissions in check (and saves fuel) at the expense of reduced power — about 40 hp less at the peak. Once the driver lifts his right foot from the wide-open throttle position, the 4-second clock resets.

This explains why the Silverado's power is low everywhere on the graph right up to the jump in power right before redline. Corresponding to the expiration of the 4-second window, the jump in power is indicative of the engine switching to open-loop "power enrichment" mode. It is only when operating in this mode that the engine delivers its full rated power.

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