The Math Behind The HellScat’s Demon slayer Dyno Pull

By Christopher R. Phillip

In the field of automotive performance, one machine stands alone for measuring the brute power of muscle cars. It’s called the dynamometer.

A dyno that can measure torque and power delivered by the powertrain of a vehicle directly from the drive wheel or wheels (without removing the engine from the frame of the vehicle), is known as a chassis dyno. (Source: Wikipedia.)

So for our Hellscat to beat the Dodge Demon at its own game — absolute power — we knew we had to trump it on a chassis dyno before we ever considered taking it down the track.

Truth be told, we don’t have a Dodge Demon in the Dream Giveaway Garage … yet. That’s where the Internet comes in. It’s quite popular among Demon owners to strap their mega-Hellcats to a chassis dyno for bragging rights. We found several of the resulting dyno graphs online. They reveal the Dodge Demon’s true horsepower at the rear wheels in between 704 to 770.

Luckily, we have a chassis dyno down the street at Bruiser Conversions. Normally, these guys use their dyno to test the power on LS-powered Jeeps they build, but they were genuinely gracious and invited us to bring our Don Garlits-tested HellScat over to them.


If you’ve never seen a chassis dynamometer in person, they’re quite the sight. A massive roller sunk partway into hollowed-out ground rotates under the mighty power of the vehicle’s wheels. The test vehicle stays strapped down on ratchet straps on all four wheels. A warehouse-size fan in front of the vehicle feeds a super-size helping of cold air onto the engine to keep it cool. Two technicians—one in the driver seat of the vehicle with a laptop running dyno software and the second monitoring a desktop app on a big LED screen—conduct the test. Oh, I forgot to mention that both technicians wear airport tarmac safety earmuffs because the test gets painfully loud.

Dyno testing is usually conducted in private so that technicians can carefully evaluate engine settings, such as: rpm, torque, horsepower, [air/fuel ratio], water temperature, oil temperature, oil pressure, fuel pressure, brake specific fuel consumption (BSFC), fuel flow, and rate of acceleration. (Thanks to Hemmings editor Tom Demauro for sharing this info.) One other very important setting monitored in a supercharged engine such as a Hellcat is boost.

If a tuner (a person who tunes the engine) concludes that the engine is not producing its full potential, he may communicate with the vehicle’s engine control module via a laptop and OBD-II interface and modify myriad parameters of the engine’s operation. His goal: maximum power without risking the life of the engine.

A dyno operator will limit the number of dyno pulls a vehicle will make, primarily for the safety of the vehicle and engine. A maximum of three dyno pulls in a session is common.

So back to our grand-prize Dodge Challenger HellScat on the dyno at Bruiser Conversions. Our first dyno pull graphed a strong 900-plus horsepower at the rear wheels. With some tuning tweaks, we blew past the Demon with a reading of 962 horsepower. That’s more than 200 horsepower beyond the Dodge Demon.

We beat the Demon on the dyno, so the next test was the track. That’s a story we’ll save for another day.

Time is running out for you to enter to win our Dodge Challenger HellScat! Use the promo code with this article to get your bonus tickets at The Challenger Dream Giveaway brought to you by Reliable Carriers, Inc. ends on June 26.