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How powerful is Hellcat? It depends…

by David Zatz on

As we try to narrow down power ratings of the supercharged HellCat Hemi V8, expected for the 2014 calendar year in the 2015 Charger and Challenger, we have to consider that rumors invariably predict much higher power ratings than we actually ever see. The current 5.7 Hemi was rumored to beat 400 horsepower; the 6.4 was supposed to exceed 525, according to some, and ended up at a not-at-all-disappointing 475 hp.

Horsepower numbers may fall because of durability testing, drivability issues, cost compromises, emissions rules, and fuel economy (though probably not in this case). Sometimes, rumored power falls by about the same amount as we’d expect to see when switching from gross power ratings to SAE net. 

When an engine is dyno-tested for initial development, it can suck down and expel all the air it wants; when it’s actually in a car, the factory exhaust and intake, constrained for space, often cuts down peak power — maybe that’s why the 5.7 liter Hemi V8 is so much stronger in Rams than in cars.

supercharged HellCat Hemi V8 engine

Then there’s the drivetrain. The ZF 8HP90 transmission has a torque limit of 900 Nm (663.8 lb-ft); Allpar would therefore expect a top limit of on HellCat of 640 lb-ft, at least with the automatic.  That compares favorably to the Viper (600 lb-ft), Corvette ZL1 (608), and Shelby GT500 (631), if it can be reached.

Current SRT engines are torque/horsepower balanced, so perhaps that 640 lb-ft will be matched by 640 horsepower, the same rating as the Viper TA, slightly more than Corvette ZL1, and 22 hp less than Shelby GT500.

Still, we believe that SRT is planning both automatic and manual-transmission versions of this engine, at least for Challenger. Perhaps the manual transmission could handle the rumored 700 hp. (Again, we have not seen any engine hit the rumored goal.)

Allpar member “mentallica” calculated that a top speed of 200 mph would require around 567 horsepower delivered at the wheels, including tire rolling resistance and wind drag (based on current SRT wind-resistance numbers). That means horsepower in the mid-to-upper 600s.

The current GT500 has a top speed of 202 mph from 662 horsepower and 631 lb-ft of torque, as measured by Ford. To beat that top speed, SRT needs to slash wind resistance from the current SRT8, or pour on the power in at least one model.  Using more efficient driveline components than competitors could cut parasitic losses, as well, — and Chrysler’s partnership with ZF has delivered more-efficient drivelines.

With production of the supercharged engines likely limited to two or three thousand per year, gas mileage is probably not a major factor in their calculations. This will be a serious pair of performance cars, sold at serious prices — and meant to put SRT back on top for a while.

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