How the Demon Runs a 9.65-Second Quarter-Mile With "Only" 840 Horsepower

Everyone expected the Dodge Challenger SRT Demon to make over 1000 horsepower. It doesn't, but it still runs 9s.

DW Burnett / PUPPYKNUCKLES

As the days drew closer to when the Dodge Challenger SRT Demon would make its debut, the rumor mill kicked into high gear. Conjecturers across social media guessed that the ultimate Hellcat would have at least 1000 horsepower—one claimed as much as 1023 hp in full-blown race mode.

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Then Dodge uncaged the beast, and announced the real numbers: 808 hp and 717 lb-ft of torque on pump gas, rising to 840 hp and 770 lb-ft with 100-octane race gas. Impressive, to be sure, but hardly the major boost over the regular Hellcat's 707 hp and 650 lb-ft that we were expecting.

So how on earth does the Demon run a 9.65-second quarter-mile at 140 mph, beating the regular Challenger SRT Hellcat by more than two seconds?

"Only 840 is a relative term," Tim Kuniskis, Head of Passenger Car Brands at Fiat Chrysler, told Road & Track at the Demon launch event ahead of the New York International Auto Show. "We're trying to move a 4200-lb. car. Everyone wants to talk about horsepower, but the most important thing is torque."

Kuniskis explained how the Demon's drag-racing equipment helps it launch off the line with an outrageous amount of torque. "A normal Hellcat, which is an amazing performance car, will leave the starting line at essentially zero boost," he said. "It'll leave the starting line at about 100 lb-ft of torque. This car, we've gone to the extreme [with] the drag radials, suspension that can give you the weight transfer to get the weight to the back of the car for the traction, and the trans brake, which is critical. The trans brake allows us to build eight pounds of boost before we launch. And now we can control that amount of power with all the traction that we have."

According to Kuniskis, with the trans brake engaged and the Demon's launch mode allowing the engine to rev and spin up the supercharger at the starting line, the newest Challenger leaves the line making more than 500 lb-ft of torque. "That's how you leave the line pulling 1.8 g," he told R&T. "You're at 60 mph and this car is still pulling 1.3 g. It never stops pulling all the way to the finish line."

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That trans brake is a tricky piece of engineering. Drag racers have long used such a device for maximum launching power. When activated, the system engages the automatic transmission's first gear and reverse gear at the same time, letting the driver rev the engine and spool up the transmission's torque converter at a standstill at the starting line. When the light goes green, the driver releases a button (in the Demon, it's the right-hand paddle shifter), which drops the reverse gear and launches the car down the track.

It's a violent process, and if you've watched any drag racing videos on the internet, you know a botched trans brake launch can grenade a transmission or differential. Not so in the Demon.

"The beauty of having a production car designed by our engineers in conjunction with [transmission supplier] ZF, is we can get around the most violent thing that happens with a trans brake," Kuniskis said. "A lot of times, when you release the trans brake, all of that torque goes immediately to the rear wheels and takes up the slack in the driveline."

It's that sudden power transfer slamming against a slack drivetrain that makes drag cars spit out their diffs and driveshafts, Kuniskis says. But the Demon protects itself against such carnage.

"The maximum RPM of the trans brake is 2350. But what's important is, because it's all electronic, we actually preload the drivetrain. We take all the slack out of the drivetrain, so you get a violent hit, but you don't get a violent hit that jars the drivetrain. That saves all the parts," he said.

So while the Demon may not have the four-figure power we've come to expect from outrageous tuner cars and drag strip dominators, it's the car's ability to put the power down immediately and effectively that blasts it deep into the 9s.

"You can't look at tuner cars as a benchmark," Kuniskis told R&T. "This is a street-legal, emissions-compliant production car with a full factory warranty."

One that just happens to run 9s.

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