Dodge Innovation Helps SRT Demon Make Gobs of Power

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Images courtesy Dodge

Colder air makes more power than hot air. There are a few reasons for this, but the main reason is that colder air is also denser air; it has more oxygen per cubic foot volume than hot air does. Super- and turbocharging the air charge entering your car’s engine is a great way to help your engine make more power, but compressing the air charger also heats it up, causing the compressed air volume to significantly lose oxygen density. This is why we recommend you use some sort of intercooler when compressing the air charge mass in your car.

Dodge’s CEO Tim Kuniskis is a man who drinks gasoline instead of coffee and has grease under his fingernails from the time he spends on the track, racing and working on race cars. So at the sit-down meeting on what was going to happen after the Challenger SRT Hellcat, he pulled the lead engineer Jim Wilder aside and told him he wanted something better than the Hellcat.

At the start, they were looking to give it the ability to regularly run in the low-ten-second range, which would have been in the area of half a second quicker than the Hellcat, but Kuniskis wasn’t happy with that.
“Jim, low-10-second cars are fast… But 9-second cars are unheard of,” he said. “How can we make it even faster?”
Wilder says that Kuniskis pushed the team to try everything under the sun to hit that 9-second mark.

Distinctive badging lets the viewer know that the power this car produces is demonic.
Some of the things they tried first were to increase the volumetric capacity of the supercharger from 2.38 liters to 2.7 liters, increasing boost pressure from 11.6 to 14.5 PSI. Next they put stiffer valve springs into the 6.2-liter engine to give it the ability to reliably run with a 6500 RPM redline (Hellcat redlines at 6200). Next they started playing around with how to make the inlet air charge even colder and came up with the SRT Power Chiller™. THAT was the one improvement over the Hellcat that bumped power output up to a staggering 840(+) using 100 octane fuel.

Normally, an engine builder or engineer is going to tell you to delete your car’s AC system if you’re building it for competition or simply to go fast. This is because of parasitic drag induced by the air conditioning compressor, both when the compressor’s clutch is and isn’t energized. The engine has to waste horsepower in order to overcome this parasitic drag.

Normally, that is. However, the Dodge engineers who brought us the 2018 Challenger SRT Demon decided that air-to-air and water-to-air intercoolers just didn’t cool the compressed air charge enough to produce the type of horsepower they were after. So, they decided to do some tubing and plumbing wizardry and use the compressed (and thus close to freezing) R-134a refrigerant in the Demon’s air conditioning system to cool the air that is being stuffed into the engine more than any other type of intercooler has. This system allows the engine to produce an impressive 808 horses on regular pump gas and up to 840 (+) horsepower when using 100 octane racing fuel.

Chris Cowland, Director of Advanced and SRT Powertrain, FCA USA LLC told reporters, “Creating a street-legal machine that is powered by an engine with unrelenting power and torque, specifically engineered for the drag strip, yet street legal and meeting all emissions, pass-by noise, and SRT durability standards demands outside-the-box thinking. The technologies that make lower-volume SRT products special can deliver significant benefits in alternative applications. For example, while denser intake air and high-octane fuels are part of the recipe that makes the Challenger SRT Demon a head-turner, they can be just as important in meeting the challenges of improving fuel economy.”

Cutaway image of the supercharger on the Demon, showing the Power Chiller™ intercooler inside the supercharger.
Dodge’s SRT division has given the Challenger SRT Demon a driver-operated control system that switches control modes between “normal, drag, and custom” modes. In drag mode, among other things, the AC system’s refrigerant is routed through the intercooler instead of the cabin cooling air box under the dash. This lets the intercooling system be as efficient as possible and chills the air charge up to an incredible 45 degrees F.

Tim Kuniskis, Dodge’s Passenger Cars CEO, considers the NHRA ban to be a badge of honor, not something to be ashamed of.

Here’s how it works in a nutshell: When the mode is set to normal, the compressed air is shunted through a normal twin intercooler system. However, there are also two more air-to-glycol (liquid coolant) intercoolers. When the driver dials up Drag Mode on the in-dash controller, refrigerant is shunted to these secondary coolers. The compressed air charge goes through to “stock” intercoolers and is then routed through these “refrigerated” intercoolers, achieving a total air charge temperature reduction of up to 45 degrees F.

The 2018 Challenger SRT Demon is the only production car designed from the ground up to be just at home on the dragstrip as on the street. It’s the only production car built with low-drag smaller tires and wheels up front and drag radials.
To handle the increased horsepower and torque that this system delivers, Dodge’s SRT engineers also had to make other modifications to the car. These include body mods to give it lower air drag/resistance, suspension mods to handle the extra torque and wild launches, engine control calibrations and brake and other driveline modifications. The result was the realization of CEO Kuniskis’ dream of a 9-second production passenger car.

Once you heat the Demon’s drag radials, they get so sticky they actually leave liquid rubber on the track.
The Guinness Book of World Records people have certified the 2018 Challenger SRT demon as the only production car to lift its front wheels on launch when in drag mode. Popular Science magazine has also named the system, called Power Chiller™, one of their Best of What’s New products for 2017 in the soon-to-be-released December issue.

The supercharger and intercooler upgrades mentioned above would be next to useless if the engine and controller mapping weren’t modified also. Thus, internally, there’s a hotter cam with more lift and duration than previous models, so the valves are open longer to fill and evacuate the combustion chambers completely.

Larger air inlet ducting and air scoop headlights increase the amount of air being sucked into the engine.
Next, there have to be some significant changes to the fuel curve mapping, because the extra boost from the larger supercharger and the colder air charge both require more fuel. So the fuel curve mapping was changed to increase the dwell of the injectors.

This picture clearly shows the larger fender flares on the Demon.
Besides the Nitto 315/40R18 street/drag radials for improved grip on launch, there were a number of others mods the engineers made because of the increased power from the engine. Body mods include fender flares that are two inches wider than on the Hellcat, required to fit those massive drag radials.

The Demon’s hood scoop’s surface area was increased to the point where it is the largest functional hood scoop on a production car with a massive 45.2 square inches of surface area. Additionally, instead of one Air Grabber air inlet duct next to the driver side headlight, now both headlights are Air-Cather headlamps, doubling the amount of air they grab for the engine.

NHRA requires that lug nuts be open top so that thread engagement can be checked. So, the Demon development team dug through their box of old stuff and came up with these open end lug nuts from their police pursuit models. NHRA legal and, even better, they save another half a pound.
Proper weight transfer at launch is vital to ensure the best launch possible. Thus, when you dial up Drag Mode, the engine isn’t the only thing affected. There are also some suspension tuning tweaks going on in Drag Mode that cause the car to squat when you release the brakes and hammer the throttle. The Drag Mode electrical suspension tweaks also make use of the wheel speed sensors to control wheel spin and wheel hop within microseconds. Both wheel spin and wheel hop are things that can destroy an ET at the track.

In drag racing, one of your main enemies is weight. That’s why you rarely see passenger or rear seats in true drag racing cars. Also, if your car does runs in the 14 second and lower range, the NHRA prohibits riders. Thus, for the true drag racer, the only seat they need is the driver seat.

Wilder put that idea to Kuniskis and he loved it, so the passenger and rear seats are optional. Unless you specifically order them, your new Dodge Challenger SRT Demon will only come with a special lightweight drag racing bucket seat for the driver, along with a race-approved four point harness. If you want them, the front passenger and rear bench seats are available as options, for a dollar apiece. Without them, you save a whopping 104 pounds, which translates to a little over a car length of advantage at the quarter mile mark.