Video: Time-Lapse Engine Build Of 840-Horsepower Dodge Demon Hemi

By Greg Acosta May 01, 2019We’ve covered some cool Redline Rebuild time lapse videos in the past, ranging from a mild small-block Ford rebuild to an 11,000-horsepower top fuel engine. However, this installment is different. Rather than using an engine that is in need of a rebuild and following along, this time, Dodge provided a brand new 6.2L Gen III Hemi out of an SRT Demon strictly for the purpose of being featured on Redline Rebuild.

Engine build time-lapse 840-hp Dodge Demon Hemi V-8 | Redline Rebuilds - S3E1

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SaveHagertyPublished on Jan 23, 2019We love doing Redline Rebuilds (almost) as much as you enjoy watching them. And when Dodge offered up the supercharged, 840-hp, Hemi V-8 out of a Challenger SRT Demon for our magical time-lapse treatment, we couldn’t say yes fast enough. Be sure to stick around until the end to watch us put that power to the ground.------------------------------------------------------------------------------


The 6.2-liter Gen-III Hemi engine takes the larger 4.090-inch bore from the 6.4-liter Hemi and mates it to the shorter 3.578-inch stroke from the 5.7-liter Hemi for 376 cubic inches of displacement. Add in the Gen-III’s awesome-flowing heads and a 2.7-liter twin-screw supercharger, along with some 100-octane gas, and you’re at 840 horsepower. From a factory engine.

In order to handle that extra power (over the 707-horsepower made from the Hellcat Engine) reliably, the block and rotating assembly have been beefed up. The engine block received revised main bearing caps to strengthen crankshaft retention, along with revised cylinder head mounting to increase clamp load against the additional cylinder pressure the Demon incurs.

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In order to withstand the extra 133 horsepower over the Hellcat engine, the Demon's block and rotating assembly have been beefed up in strategic areas. Revised main caps, a stronger crank, beefier rods and rod bolts, and enhanced pistons are all parts unique to the Demon Hemi.

Internally, a stronger forged crankshaft than what was used in the still-impressive Hellcat is employed, to be able to thrive with additional boost, horsepower, and RPM. In addition to the crankshaft, the connecting rod forgings have been beefed up at both ends and upgraded rod bolts have been added.

The 4.090-inch pistons have also been enhanced, with additional thickness under the crown and skirt to withstand the constant barrage of horsepower. To keep those slugs cool, the piston oil squirters have been enhanced to provide additional cooling capacity and oil flow. New factory bearings and bearing clearances have also been specified to help the engine live at the higher horsepower levels and the slightly elevated engine RPM.
Moving to the top end, we can see part of the reason for the increase RPM capability in the Demon, with revised single-groove locks on the hollow intake, and sodium-filled exhaust valves The factory beehive valvesprings have also been given an increased spring rate, not only to handle the higher RPM, but also the more aggressive camshaft profile. Like the pistons, the valvesprings receive additional oil flow in the Demon to increase valvetrain cooling.

The Demon’s more aggressive camshaft profile still utilized hydraulic roller lifters, and makes use of up to 17 degrees of variable cam timing while the Multi-Displacement System (Dodge’s DOD/AFM) remains deleted, as in the Hellcat engine.
It’s not just the short-block that was enhanced. Dodge made significant changes to the valvetrain for an additional 300 rpm of factory engine speed. Hollow intake and sodium-filled exhaust valves, higher-rate beehive valvesprings and a different valve lock design.
It might be said that all these upgrades are supporting players to the biggest source of the Demon’s increased power – the upgraded 2.7-liter IHI twin-screw supercharger. With a solid 320cc/revolution airflow increase over the 707-horsepower Hellcat it’s no surprise there’s more power to be made. In addition to an increase in flow, the new supercharger is allowed to make almost three pounds more boost by the ECU, with a new factory boost limit of 14.5 psi.

The boost is fed through a charge cooling system that sits on top of the blower, in an arrangement that is “upside-down” of a traditional blower/cooler configuration. As we can see in the final seconds of the video, the dual spark plug coil-on-plug ignition system is retained in the Demon.

It’s not often we get such a stylized look inside of an OEM powerhouse engine, but thanks to Dodge and Haggerty this was possible. Now, would it be too much to ask to see the same thing done with a Hellephant?Possibly the star of the Demon show, the upgraded 2.7-liter IHI twin-screw supercharger. In addition to increased volume capability over the Hellcat’s 2.385-liter unit, boost has also been increased to one full bar (14.5 psi) of pressure.

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Part 2