Dodge Challenger Forum banner

1 - 13 of 13 Posts

·
Registered
Joined
·
10,541 Posts
Discussion Starter #1
http://articles.sae.org/13227/

Long-rumored to be in development, Chrysler's super-high-output Hellcat Hemi is Chrysler's first production supercharged V8. Note squat and compact supercharger shown above the cylinder block in this CAD rendering.



Powertrain engineers love understatement—as well as a bit of deception. That was made clear recently when Chrysler announced that its new "Hellcat" Hemi V8 will be SAE J1349-rated at 707 hp (527 kW) and 650 lb·ft (881 N·m) when it debuts in the 2015 Dodge Challenger SRT. The latest iteration of the fabled Hemi is by far the most powerful production engine in Chrysler history, making the Challenger the most powerful muscle car ever.
Automotive Engineering in early June reported Chrysler's "teaser" output numbers for the supercharged 6.2-L V8, which SRT Powertrain Director (and Chrysler Advanced Powertrain development head) Chris Cowland told us would be "in excess of 600 bhp and torque above 575 pound-feet." Strategic understatement, indeed. Named after the famous WWII Grumman F6F fighter plane—Mustang was already taken, we note—the 6.2-L Hellcat shows the Hemi architecture it’s based on still contains plenty of room for development.
This is the first production Chrysler Hemi V8 to feature a factory-engineered supercharger system. Supplied by Japan’s IHI Corp., the blower is a Lysholm type (twin-screw) positive-displacement unit, belt driven from the crankshaft. As opposed to a more traditional Roots-type supercharger with rotating lobes, the Lysholm compressor pushes intake air that’s received from the car’s large, functional hood scoop through a pair of close-meshing screws that resemble worm gears. The design features relatively low parasitic losses and air-leakage levels compared with Roots-type machines.
According to Cowland, his team “evaluated all of the current supercharger suppliers during the early stages of the program, relative to efficiency, power and torque requirements. IHI was selected as the best match to our requirements,” he said. The unit’s design and specifications were developed jointly between Chrysler Group SRT and IHI, he noted.
Displacing 2380 cm³, the IHI blower has integral charge coolers and an integrated electronic bypass valve to regulate boost pressure up to 11.6 psi (80 kPa). Its twin-screw rotors feature a proprietary coating containing PTFE and polyimides which enable closer rotating tolerances and help reduce air leakage for greater operating efficiency. The new supercharger has a 2.36:1 drive ratio and 14,600-rpm maximum operating speed. It uses synthetic lube and is sealed for life. A one-way clutch provides operating refinement without detracting from the mechanical “blower noise” that SRT fans adore.
Better known as a turbocharger specialist, IHI’s Lysholm-type superchargers have been used by AMG Mercedes (the S55 V8) and Mazda (Miller-cycle V6). Compared with a twin-turbo setup, the development team felt a supercharger would offer “a better match to the vehicle characteristics we were targeting, specifically instant throttle response and low-speed torque,” Cowland explained.
The Hellcat uses a mass-airflow sensor for bypass, throttle and OBD controls, Cowland said. The 92-mm throttle body is the largest ever used on a Chrysler vehicle and is supplied by a twin-inlet, 8.0-L air box.
For a Chrysler Powertrain video featuring the Hellcat V8, see: http://www.youtube.com/watch?feature=player_embedded&v=VAQqDyy8Fa0
Beefed up lower end
Asked why Chrysler’s highest-output V8 was developed around the 6.2-L displacement (103.9 x 90.9 mm bore x stroke), when Chrysler already had the 6.4-L (103.9 x 94.6 mm) version, the so-called 392, which is also available in the 2015 SRT Challenger, Cowland replied that the development team chose to destroke the 6.4-L in order to increase the strength of the crankshaft. He said 90% of the engine content is new compared with the 392.
While Chrysler’s original business plan for the modern-era (2003 to present) Hemi included a cast-aluminum cylinder block, production engines have retained the iron block for cost reasons, according to a ranking Chrysler executive. Despite the ability of an aluminum block to lighten the front of the vehicle by 50 lb (23 kg) or more, Chrysler Powertrain engineers have stuck with the iron casting due to the Hellcat’s increased bearing loads, compared with those of the naturally-aspirated 392.
The supercharged high-output Hemi demands “very high-strength block bulkheads, and cast-iron offers the best solution within the geometry of the Hemi family,” Cowland explained.
Accompanying the robust iron block are heavy-duty main bearings supporting a forged-steel crankshaft with induction-hardened bearing surfaces. The crank is capable of withstanding firing pressures of nearly 1600 psi (110 bar). Cowland noted that the increased peak cylinder pressure of the Hellcat version required significantly strengthened connecting rods and pistons, the latter being forged and featuring wrist pins with a special diamond-like-carbon coating.
The Hellcat V8 is not equipped with Chrysler’s cylinder deactivation system that’s used on the standard Hemi. It does feature an active-exhaust system, however. See video: http://www.youtube.com/watch?feature=player_embedded&v=m00JN6P2X6M. The non-SRT Challenger’s active exhaust is supplied by Faurecia. For more on the 2015 car, see http://articles.sae.org/13100/.
The trick “Valet Key”
Chrysler’s powertrain and electronics engineers have created a clever solution to ensuring all 707 of the Hemi Hellcat’s horses won’t be accessible to just anyone (parking valets, teenage drivers) who slips behind the SRT Challenger’s wheel. When equipped with the Hellcat engine, the car comes standard with two key fobs, a red one and a black one.
The red fob is the one that unlock’s the full Hellcat fury, explained Russ Ruedisuelli, head of SRT and Motorsports engineering. The black fob you give to the lead-footed parking valet, because when you turn on the ignition with it, the engine controller signals a reduced-output engine map, limiting peak revs to 4000 (and max output to 500 hp/373 kW). It also locks the Chrysler-built, ZF-licensed 845RE eight-speed automatic transmission out of first gear, while upshifting earlier than normal. It also disables the steering-wheel paddle shifters and launch control, and sets the car’s traction, steering and suspension to their “Street” settings.
Supplementing the new V8, the SRT Challenger also gets a new, selectable Driver Mode system, which Ruedisuelli said “allows a choice of shock settings, steering assist levels, horsepower, traction setting, auto transmission calibration, and shift points. There are over 125 different settings.” The 2015 Hellcat will be available with a Tremec six-speed manual in addition to the 845RE.
Final drive ratio on Hellcat-powered cars is 3.70:1 for the six-speed Tremec manual gearbox, and 2.62 for the automatic. Driveline upgrades include prop shafts, half shafts, axles, and cooling.
 

·
Registered
Joined
·
4,316 Posts
Thats a great post! Really interesting to read the rationale behind de-stroking the 6.4 down to the 6.2 level in order to beef up the crankshaft. It really speaks alot to the loads being put onto the bottom end. It was also intereting to see they stayed away from the MDS - even in the reduced engine map black fob configuration. I think with all the limits they are pushing on this vehicle, getting rid of MDS was very smart.
 

·
Registered
Joined
·
2,577 Posts
Even though it is a good read, I wish they would have done more research. The black key fob is not the reason the car is in valet mode.
 

·
Registered
Joined
·
10,541 Posts
Discussion Starter #5
Even though it is a good read, I wish they would have done more research. The black key fob is not the reason the car is in valet mode.
Maybe I misread it, but the information above about the black keyfob limitations/"valet mode" appears to be the same information posted on the driveSRT.com Hellcat site. Did I miss something? :4-dontknow:
 

·
Premium Member
Joined
·
18,504 Posts
Interesting read Bob ! I'm wondering what measures are in place to prevent bugs and road dirt from entering through the fog lamp vents ?
 

·
Registered
Joined
·
10,541 Posts
Discussion Starter #7
Interesting read Bob ! I'm wondering what measures are in place to prevent bugs and road dirt from entering through the fog lamp vents ?
I've been wondering the same thing.
With an 8-liter airbox, I can't imagine not having some type of screen or "pre-filter" in that intake with the crap that'll get sucked in there.
Driving through swarms of bugs in rural New Jersey around 6:00 am a few years ago made my Challenger look like she had a beard - literally! That would have starved the Hellcat intake pretty quickly without some system in place to reduce the crud coming in from the front.....
I can't imagine replacing or cleaning the air-filter every few hours. Perhaps the headlight-intake is only active/open under full throttle, using the standard wheel-well intake under "normal" driving conditions? :4-dontknow:
 

·
Registered
Joined
·
22,670 Posts
Good read with good information, thanks for posting that.
 
  • Like
Reactions: 09ChallengerDad

·
Registered
Joined
·
8,503 Posts
Bob, very good article and thanks for posting! Underrated and deception? I wonder if that translates into hidden horsepower and torque potential?
 

·
Registered
Joined
·
10,541 Posts
Discussion Starter #10
Bob, very good article and thanks for posting! Underrated and deception? I wonder if that translates into hidden horsepower and torque potential?
Thanks for the kind words! :smileup:
Chris Cowland said that the engine was actually producing close to 800 HP, but the immediate parasitic loss for driving the IHI supercharger saps about 80 HP from the output before the power even reaches the crank.
He also said that the ECU is "locked" (SOP for Chrysler), and that they hadn't had a chance to see how much could be "tuned" out of the engine - they were only concerned about durability and final production HP/TQ numbers to get to the assembly line.
I'm quite sure that this beast can be twisted to around 900 crank HP without internal changes. Johan and Mike will have to get busy when they finally get their hands on one. :D
 

·
Registered
Joined
·
2,577 Posts
Maybe I misread it, but the information above about the black keyfob limitations/"valet mode" appears to be the same information posted on the driveSRT.com Hellcat site. Did I miss something? :4-dontknow:
The black fob limits the car to 500 horsepower for everyday driving. In order to go into valet mode, you need to select it from the drive modes menu and enter a 4 digit pin. Utilizing the black fob by itself does not put in valet mode.
 

·
Registered
Joined
·
10,541 Posts
Discussion Starter #12

·
Registered
Joined
·
10,541 Posts
Discussion Starter #13
The black fob limits the car to 500 horsepower for everyday driving. In order to go into valet mode, you need to select it from the drive modes menu and enter a 4 digit pin. Utilizing the black fob by itself does not put in valet mode.
I understand what you're saying, but I think it's merely a matter of sematics. Regardless of what mode it's called, using the black fob will place great limitations on the driver as opposed to using the red fob (unless Valet Mode is enabled by the owner). :smileup:
 
1 - 13 of 13 Posts
Top