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Cars Explained: Hellcat Engine

Niel Stender

Dodge may have made their name with the HEMI, but they’ll go down in history as the most audacious automaker ever thanks to their wild Hellcat engine.

Dodge Loves the Hellcat Engine – and So Do We

Kudos to Dodge for creating an entire brand around a motor, that being the Hellcat. The automaker’s marketing centers around big cruisers wielding thunderous V8 power plants, ready to roast a set of rubber at a moment’s notice. And for good reason. The Hellcat engine is a modern marvel of motor engineering, sporting a supercharger to help produce massive power figures. Let’s take a look at what makes a Hellcat so special.

Improving the V8 Engine

6.4L HEMI V8 Engine - media.stellantisnorthamerica.com
6.4L HEMI V8 Engine - media.stellantisnorthamerica.com

Dodge has made themselves synonymous with HEMI and V8. Though their modern powertrain lineup doesn’t quite hit the dictionary-definition of a hemispherical combustion chamber, no one minds when said motor makes over 700 horses. HEMIs span a range of displacements from 5.7-liters up to the 6.4-liter Apache V8 fed by natural aspiration. The Hellcat block houses 6.2 liters of displacement and utilizes forced induction in the form of an IHI, twin-screw supercharger.

Like its Chrysler brethren, the Hellcat engine foundation is a cast iron block with 103.99 mm bores, but aside from that, 91% of the motor is new content. Thicker block webbing and revised water-jacket geometry, around the top of the cylinders, is added to support the increased power and resultant stress. A hardened-steel crankshaft utilizes induction-hardened journals for improved impact and wear resistance.

Dodge Durango SRT Hellcat - dodge.com
Dodge Durango SRT Hellcat - dodge.com

Powder-forged steel connecting rods are made of a proprietary alloy blend and use cracked bearing caps for more secure crankshaft clamping. The pistons are also forged from an in-house developed aluminum alloy, giving them the strength to withstand more than 21,000 pounds of combustion pressure. They swing on floating, 24 mm wrist pins with a “Diamond-Like Carbon” coating to keep friction minimized. Piston cooling jets are added to keep piston crown temperatures down.

The aluminum cylinder head uses the same architecture as an Apache 6.4 as well as hollow-stem valves. However, Hellcat exhaust valves are filled with sodium to sustain temperatures up to 1,472 degrees Fahrenheit. They’re also massive, with a head diameter of 42 mm, while the intake valves measure 54.3 mm. While direct injection was considered, high-pressure delivery pumps with the needed capacity do not exist. The eight fuel injectors deliver 630 cc of gasoline per minute, which is equivalent to filling a pint glass every six seconds.

How the Hellcat’s Supercharger Works

Dodge Hellcat screw compressor - briansmobile1 on YouTube.com
Dodge Hellcat screw compressor - briansmobile1 on YouTube.com

On the air side of things, an IHI manufactured twin-screw supercharger rams as much ambient air as possible into the Hellcat. A pair of outdoor air intakes lead the way, one at the center of the driver’s side headlight and another via an under hood housing.

First, the air courses through Dodge’s “Super Chiller” heat exchanger, which uses the air conditioning system refrigerant to begin the cooling process ahead of the supercharger. Spinning at up to 14,600 rpm, the 2.4-liter blower compresses that intake charge and then runs it through dual, integral charge coolers to further reduce the temperature.

Dodge Hellcat dual coolers - briansmobile1 on YouTube.com
Dodge Hellcat dual coolers - briansmobile1 on YouTube.com

An electronic bypass valve, within the supercharger, keeps boost pressure regulated while a 92 mm throttle body – the largest in use on any Chrysler vehicle – lets it all flow. Post-combustion gases are exhausted via a pair of 2.75” straight pipes that feature a custom-engineered note, modulated with an electronically controlled exhaust valve.

Internally, the supercharger rotors are coated with a Teflon-like material to maintain the tight clearances needed to prevent air leakage. Special washers, infused with industrial diamonds, are used to secure the blower’s pulley belt to the crankshaft while providing sufficient clamping friction. To keep everything lubricated, Penzoil developed a 0W40 viscosity, Ultra Synthetic engine oil that is run through a high capacity cooler.

More Than Just an Engine Upgrade

2015 Dodge Challenger SRT Hellcat - media.stellantisnorthamerica.com
2015 Dodge Challenger SRT Hellcat - media.stellantisnorthamerica.com

All this engineering adds up to ludicrous levels of power. When the Hellcat engine debuted in 2015, it was making 707 horsepower in the Dodge Challenger. Currently, that figure is 717 with 656 lb-ft of torque in Challenger and Charger duty.

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All that grunt is put to the rear-wheels via a six-speed manual or eight-speed automatic in the Challenger while the Charger Hellcat can only be had with the automatic. In both cases, transmission lubricant coolers are added to keep up with the extra thermal load.

Brembo brakes - media.stellantisnorthamerica.com
Brembo brakes - media.stellantisnorthamerica.com

Of course, braking and handling need an upgrade to handle all this juice. Brembo lends its expertise here with gigantic, 15.4” front rotors clamped by six pistons. Out back, the rotors are 13.8” in diameter with calipers housing four pistons. An active damping suspension system, developed with Bilstein, has driver-selectable settings of Street, Sport and Track that adjust shock valving based accordingly.

Hellcat Engines Across the Lineup

2021 Jeep Grand Cherokee Trackhawk Hellcat - media.stellantisnorthamerica.com
2021 Jeep Grand Cherokee Trackhawk Hellcat - media.stellantisnorthamerica.com

It didn’t take long for Dodge to spread the Hellcat love across its family of brands. In Dodge Durango application, the motor is slightly detuned to produce 710 horses and 645 lb-ft of twist. The Ford Raptor eating, Ram 1500 TRX makes “only” 702 ponies with its Hellcat engine and Jeep gets in on the fun with the Jeep Grand Cherokee Trackhawk cranking out 707 hp.

Going truly crazy, the Dodge folk cooked up a high-output Hellcat variant known as the Redeye. Available in the Charger and Challenger, it produced just shy of 800 horsepower. A Super Stock Challenger cracks that mark with 807 hp on hand, which is a subtle bow of submission to the penultimate Hellcat-powered vehicle.

2018 Dodge Challenger SRT Demon - media.stellantisnorthamerica.com
2018 Dodge Challenger SRT Demon - media.stellantisnorthamerica.com

Only produced for one year, 2018, the Challenger SRT Demon came with drag radials from the factory, churning out 808 horsepower when run on 91-octane pump gas. Filling up with 104-octane race fuel and dropping in the special, factory-supplied ECU turned things up to an incredible rating of 840 horsepower.

Drop a Hellcrate in Almost Anything

"Hellephant" Crate - media.stellantisnorthamerica.com
"Hellephant" Crate - media.stellantisnorthamerica.com

Thinking about how cool it would be to drop a Hellcat engine into that BMW 5-series wagon project you’re working on? Dodge has you covered with their pun-tastic Hellcrate program. For a seemingly reasonable $20,215, you can buy a crate filled with a 707 hp 6.2-liter, supercharged Hellcat engine. An engine kit to hook everything up costs $2,265 and the front-end accessory drive setup runs about $700. You can even buy the Tremec six-speed manual transmission for $5,250.

If that’s not bold enough, you can also purchase the Redeye variety Hellcat for a couple thousand bucks more. But if you’d prefer to bend your Bimmer’s entire chassis upon first launch, don’t miss the Hellephant crate engine. Displacement jumps from 376 to 426 cubes and power is an eye-watering 1000 horsepower and 950 torques. It runs on pump gas and costs an even thirty grand.

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Niel Stender
Niel Stender

Niel got his start in the car world as a vehicle dynamics engineer with SVT at Ford. He still has dreams of running figure eights on the wet pad in an S197 GT500. These days, when not fending off karate kicks from the 3 tiny humans that run his household, he can be found on St. Louis backroads pretending to be Ken Block in his 6-speed Mazda 6.

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