Watch The Dodge Challenger SRT Demon's 840-HP V8 Engine Scream On the Dyno

It had to be factory-tested on a setup originally designed for NASCAR engines.

YouTube | DPC Cars

The candles have been lit, the incantation is nearly complete, and the Dodge Challenger SRT Demon is about to be summoned by dealers nationwide. But before that happens, take a moment to appreciate the extreme testing done on the 840-horsepower supercharged V8 engine in order to sharpen the knife of a car that, in the words of The Drive editor Mike Guy, "hates humans."

To wring out every last bit of power from the Hellcat's existing 6.2-liter engine, the tiny crack team of FCA SRT engineers worked in near-total secrecy to redesign over 60 percent of the internals, including the cast-iron block, high-strength alloy pistons, powder-forged connecting rods, and crankshaft. They also rigged up the car's special air intake chiller system and rigged the whole thing to run on 100-octane gas. Parts suppliers were given the bare minimum details to work with, sometimes just a target figure, and internal simulator work helped piece everything together. 

Of course, testing a screaming V8 engine that's being covertly developed poses its own set of challenges. The SRT crew was able to do most of the work in their own building down the road from FCA's main campus in Michigan, but they still needed to use the larger facility's engine dyno setups to dial everything in. In order to keep the banshee's howl from giving everything away, tests were originally conducted on nights and weekends.

Later, a more clever solution emerged—altering the dyno display screen to always read 707 horsepower, so anyone walking by would think they were just testing a plain-Jane Hellcat engine. There was more than one problem, though. Despite using a setup at FCA's headquarters that was originally designed for NASCAR engines, they were still limited by the building's fuel delivery system, which almost couldn't keep up with the engine's insane 1.36-gallons-per-minute appetite at full blast. 

The video above shows one of these tests, and pay attention to the numbers at bottom left (and the red-hot exhaust pipes). Those 840 horses get all the attention, but it's the Dodge Demon's sky-high torque figures that get it off the line for that vaunted nine-second quarter-mile run. At a relatively tame 4500 RPM, the engine is already putting out almost 660 horsepower and 770 lb.-ft. of torque. That's already more than the peak figures for the Chevrolet Camaro ZL1 1LE, and it's just getting started.