with thanks to Danno, oh2o, JRS200x, and AutoTechnician • See “Deeper into the Hellcat”
The supercharged 6.2 Hemi has 707 horsepower and 650 lb-ft of torque. This engine is available alongside the 6.4 Hemi in the 2015 Charger, 2015 Challenger, and possibly the Jeep Grand Cherokee Trackhawk.
The drop from the SRT 6.4 liter engine to 6.2 liters was caused by a reduction in stroke, which was done to increase the strength of the camshaft, according to SRT powertrain chief Chris Cowland. It does not, despite early rumors, have MDS / cylinder shutoff.
The Hellcat Hemi is hooked up to a manual transmission in Dodge Challenger, and an eight-speed automatic in Challenger and Charger; the 8HP90 can handle up to 663 lb-ft.
Advances in superchargers could boost power even more — learn how.
Before launch, Mike wrote that Hellcat-equipped SRT8s have two power modes, which he described as “street and kill. I believe the street mode is just a little more powerful than the normal SRT. Kill mode, as I call it, is just clinically insane.” Dodge’s press release has the two modes activated by choosing one’s key fob: the black fob limits the engine to 500 hp, while the red one taps the engine’s full potential of 707 horsepower.
“fargo59” wrote that it shares heads with the Apache SRT 6.4 Hemi engine. “A 6.4 with a forged 5.7 crankshaft would give the right dimensions and be relatively easy to work; a shorter stroke is also going to give the ideal rod to stroke ratio and make it a high revving engine.” Cams are also reportedly similar to the 6.4 design; the block is said to be identical. (The block is the same, cast iron for strength.)
“Danno” wrote, “Air comes in through the front of the blower, and is compressed upwards, goes through runners, makes a 180° turn, and goes straight down through the four heat exchangers (one for each pair of cylinders), then into the intake ports. The fog lights have been replaced by vents for the low-temperature oil/coolant radiators; an opening in the wheel well lets the air flow out. One side is an oil cooler the other side is coolant. The coil covers say ‘supercharged HEMI.’”
The supercharger was provided by IHI, which also sells superchargers to AMG (higher-performance Mercedes). They worked with Chrysler to develop the specifications and design of the supercharger. Turbochargers were considered but the supercharger provides better “instant-on” torque.
The 2,380cc/rev blower has integral charge coolers (sometimes incorrectly called “intercoolers”) and an integrated electronic bypass valve to regulate boost pressure, up to 80 kPa (11.6 psi). Its twin-screw rotors are specially coated with a proprietary formula of polyimide and other resins; nanometer-sized, wear-resistant particles; and solid lubricants, such as PTFE (Teflon). The coating accommodates tighter tolerances, cutting air leakage for higher efficiency.
The new supercharger, sealed for life with synthetic oil, has a drive ratio of 2.36:1 and a maximum speed of 14,600 rpm. The one-way clutch de-coupler improves refinement without detracting from the engine noise. The supercharger gulps air through an Air Catcher inlet port, which replaces the driver’s-side inboard marker light and connects to a twin-inlet, eight-liter air box; the 92 mm throttle body is the largest ever used in a Chrysler Group vehicle.
The in-tank fuel pump accommodates variable pressures, half-inch fuel lines, and eight injectors, each capable of delivering a flow rate of 600cc/min – enough to drain the fuel tank in around 13 minutes at full power.
The large-nosed crank drives a high-flow gerotor oil pump that feeds a lubrication circuit servicing eight high-flow piston cooling jets. A high-capacity oil/air heat exchanger, mounted in the front of the car, mitigates oil temperatures when driving conditions are harshest. The 0W-40 synthetic oil was developed for SRT by Pennzoil.
Additional cooling measures include a low-temperature circuit with two air/coolant heat exchangers integrated into the supercharger housing. This setup is designed to keep air temperatures below 140° Fahrenheit (60° Celsius) under extreme ambient conditions, while enabling air flow of up to 30,000 liters per minute. It is effective enough that engine power will not be de-rated due to cooling demands, even after 20 laps of a grueling 3.1-mile road course at an ambient temperature of 100° Fahrenheit.
The exhaust note was custom-engineered using an electronically controlled exhaust valve; the first time a 2015 Dodge Challenger SRT Hellcat was fired up on the assembly line in Ontario, workers came running to investigate. The 2.75-inch, straight-through, twin-exhaust system includes durable, double-walled exhaust manifolds and ceramic catalysts capable of withstanding temperatures up to 1,922° Fahrenheit (1,050° Celsius).
SRT Powertrain director Chris Cowland wrote, “The increased peak cylinder pressure of the Hemi Hellcat required that pistons, conrods, and crankshaft were all upgraded. The pistons are forged, high-strength alloy and the piston pins use diamond-like-carbon coating. Ninety-one percent of the content is new.”
Mr. Cowland added that MAF (mass airflow sensors) are used bypass, throttle, and OBD controls.
New tests were required to validate engine durability, requiring new laboratories with new dynamometers. The development teams conducted almost 2 million customer-equivalent hours of dynamometer testing on the Hellcat. Road tests included numerous high-speed runs in severe climate conditions and a strenuous 24-hour track testing program at the Nelson Ledges, infamous for its harsh surfaces. Engineers subjected the car to 125 consecutive drag starts. Every engine gets a 42-minute dynamometer shakedown before it is shipped.
The fastest Mopar four-seater ever made was the Dodge Charger Daytona, which broke the 200 mph barrier in 1970, thanks to the hot 426 Hemi V8 and a great deal of time in wind tunnels. Can the new Charger or Challenger meet or beat that time?
Forum member “AutoTechnician” wrote, “The power required to overcome aerodynamic drag increases with the cube of the speed (e.g. 20 mph requires eight times the power as 10 mph to push through the air.) Factor in mechanical losses, rolling resistance, etc... and you're easily well over 600 hp required at the crankshaft to do 200 mph. The 638HP ZR1 can only do 205 mph.” The efficient eight-speed automatic and ZF axle may help SRT by cutting parasitic losses.
“AutoTechnician” took the details of the Challenger Hellcat and added the 392’s published power and top speed (475 hp, 182 mph top speed) to chart the Hellcat’s top end. The chart, for illustration only, is at right; it shows 198 mph at 600 horsepower, and 214 mph at 700 horsepower. He assumed a 5,800 rpm redline, based on Dodge’s photo of the SRT’s gauges; however, Hellcat makes peak power at 6,000, so the redline is probably a bit higher.
Source “Danno” wrote that the Hellcat Challenger hit 202 mph in testing; production cars might not, as changes were made to enhance cooling and durability. With 707 hp, the final word is still on its way.
Chrysler engineer Chris Cowland revealed numerous new details about the supercharged Hemi engine used in the Dodge Challenger SRT Hellcat.
The HellCat is named after a Grumman World War II fighter plane, used mainly on aircraft carriers; many of its 2,000-hp Pratt & Whitney engines (also used on Corsair and Thunderbolt) were made by Nash, the car company that later joined with Hudson to form AMC, which was purchased by Chrysler in 1987.
Around 12,200 Hellcats were made in a little over two years. They destroyed 5,223 enemy aircraft, more than any other Allied naval planes; the Hellcat’s overall kill-to-loss ratio was around 19:1, beating every Japanese aircraft by at least 4:1. Only 270 were downed by aerial combat during the war (most of the planes that were lost, fell to training accidents or transport problems).
In 1943, Admiral D.C. Ramsey sent a letter to workers at Nash, praising the engines, and relayed a pilot’s report: “The Pratt and Whitney engine [many of which were built by Nash] performed admirably with no blower difficulties and few exhaust stack failures.”
“HellCat” is only an internal project code; other names include Hurricane (four cylinders), Eagle (5.7 Hemi), and Apache (6.4 Hemi).
See “Deeper into the Hellcat”This is a 370 cubic inch, 90-degree V-type engine. There are 16 pushrod-operated overhead valves, with hollow-stem intake valves and sodium-filled exhaust valves; the conventional hydraulic lifters have roller tips. The exhaust starts out with dual three-way catalytic converters, which dump into dual 2.75-inch pipes and a straight-through exhaust system, with twin electronic exhaust valves and rectangular black chromed tips.
A separate low-temperature cooling system reduces the heat of the incoming air; there are dual water-to-air charge air coolers and a high-flow, variable-speed electric water pump.
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