A Look Inside The Dodge Demon’s 840-hp HEMI
http://www.hotrod.com/articles/look-ins ... 40hp-hemi/
Is the Dodge Demon’s 840hp, 6.2L Supercharged Hemi a Hellcat engine with more boost? Conclusively, no it is not. Instead, it’s a highly revamped mill with 62 percent new componentry. The engine will be produced alongside Hellcat engines in the Saltillo engine plant in Ramos Arizpe, Mexico– but that is where the similarities end. Dodge opened the engineering logs and gave us a real look at the guts required to make world’s quickest production car.
When you aim to make more horsepower than seven Ford Fiestas combined, pass emissions, and carry a full warranty, a sturdy foundation is paramount. The Demon’s engine begins with a new, beefed-up block. Although bore and stroke are identical to the Hellcat, (103.9mm bore and 90.9mm stroke), the block features substantially reinforced main caps for increased clamp load and rigidity. The deck surface gets the same treatment to increase clamp load on the cylinder heads and contain the increased horsepower. In order to keep the bores true with the extra load from the head bolts, a torque plate is used––a process not performed on the Hellcat. The plate simulates the stress of a torqued cylinder head so that the bores can be honed perfectly round. The oiling system has been revised with a high-flow gerotor pump. Additional oil flow is directed to the top end as well as to oil cooling jets that spray twice as much oil as those used in the Hellcat. Completing the oiling system are a redesigned pan and oil pickup built to cope with the demands of 1.8g launches.
The crankshaft, connecting rods and pistons are all completely unique to the Demon. The crankshaft is a forged alloy unit that received revised balancing and induction hardened bearing journals. The connecting rods are burley powder-forged units with upgraded shanks, big ends, tapered small ends to reduce weight, and ultra-high tensile strength ARP 2000 fasteners. The pistons are also forged and feature an inclined box well design for additional wrist pin support. Piston to wall clearance was increased 30 microns to accommodate both piston alloy and the heat expansion associated with the Demons 840 horsepower power level. At peak power there is a compressive loading of 11 tons on the piston and connecting rod so all of the internal components had to be up to the monumental task at hand.
Heads and Valvetrain
In order to get more air into the engine post-supercharger and help increase durability, both cylinder heads and camshaft were optimized. The cylinder heads are cast from A356-T6 aluminum for its strength and heat-shedding properties. A new, gun-drilled, hydraulic-roller camshaft bumps the sodium-filled valves to the tune of .561-inches of lift on the intake and .551-inches on the exhaust. Lobe duration specs in at 224 degrees on the intake and 240 degrees exhaust (measured at .050-inches of lift). The new valve opening and closing points actually reduce intake and exhaust overlap from the grind used in the hellcat. A hydraulically actuated variable valve timing system is used to alter the cam’s installed centerline 17 degrees for improved power across the rev range.
Up top, 33 percent more oil is metered to the valvetrain via a larger diameter orifice in the headgasket, where oil passes from the block gallery to the cylinder head. This oil is instrumental in cooling the valvesprings, which dramatically effects their service life, and better lubricating the rocker arms.
Fuel and 100-Octane Systems
To feed the massive horsepower the Demon is capable of creating, the fuel system needed a boost. Twin, in-tank pumps feed injectors similarly sized to the Hellcat, but with an increase in overall fuel system pressure. The 100-octane mode, included with the $1 Demon Crate, allows the car to increase peak power when activated. The system needs a minimum of 100 average octane in the tank and will actively disable the mode if it detects knock. The real advantage in power and torque in this calibration is the ability to add spark advance due to the higher-octane fuel’s resistance to detonation. At peak torque in 100-octane mode, the spark is advanced 8 degrees for a 53lb-ft bump. At peak power, spark is advanced only 5 degrees for an additional 32 horsepower. Engineers were quick to point out that additional ignition timing at peak power did further amp up power production, however it eclipsed the parameters of their design window. Chris Cowland, head of Advanced and SRT Powertrain, explained that the engine is design for a max cylinder pressure of 135Bar and increased ignition timing eclipsed that threshold.
Supercharger and Intercooler
The blower atop the demon’s 6.2l Hemi isn’t a pulley’d up hellcat blower. Instead, it’s a revamped air mover with a re-profiled inlet and extra .3 liters of displacement. This comes courtesy of a 1-inch longer rotor-pack supplied by IHI. The rotors are a twin-screw design with 5 lobes on the larger, driven rotor and 3 on the smaller, faster spinning rotor. The pulley ratio is identical to the hellcat (2.36:1), though the larger blower is able to supply 14.5psi of peak boost pressure, up 2.9 psi from the Hellcat. The one-way or “overrun” clutch on the supercharger is retained and helps keep the mass of the supercharger rotors, which turn 15,340rpm at full song, from damaging the belt during rapid deceleration.
Keeping the newfound airflow cold is an industry-first refrigerant-based cooler. Dubbed the “SRT Power Chiller,” the system is one half of a dual-fold intercooling system. A conventional air-to-water intercooler with heat exchangers mounted in the intake manifold, under the blower, is fed coolant from a 45lpm electric pump and works consistently to cool the intake charge. When Drag mode is engaged, refrigerant is routed into an additional heat exchanger that uses refrigerant temporarily borrowed from the air conditioning system to further cool the intake charge. When both systems are humming simultaneously, the system can create temperature drops of almost 90-degrees Fahrenheit.
Secrets and Validation
One of the wildest accomplishments of the Demon program was keeping its ultra-high-power mill secret for such a long time. The facility it was developed in is massive and there are lots of folks from other brands shuffling around the complex. The sources for a leak are endless, but the SRT Engineering team persevered. In order to hide the 800hp-plus numbers from prying eyes during durability and development testing, engineers cleverly recalibrated the dyno cell to read lower, just in case anyone was looking that shouldn’t be. When the time came for SAE (Society of Automotive Engineers) validation, the dynos––actually “dyno,” as only cell C07 was rated to handle the power the Demon was putting down––were recalibrated. To comply with SAE regulations, the engine had to be run in as-installed condition. Every accessory, intake, and exhaust restriction, including catalytic converters and mufflers were installed for the test. The engine was pulled for minutes at a time at every test RPM until power stabilized, which took an excruciating 45 minutes, to accomplish. The end result was a bonafide 808 horsepower at 6,300 rpm and 717 lb-ft at 4,500 rpm with premium 91-octane fuel and 840 horsepower at 6,300 rpm and 770 lb-ft at 4,500 rpm on 100-octane juice.
What a beast. I need one of these in my RAM.