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How fast can HellCat go? (Update)

by David Zatz on

HellCat challenger

ZF’s eight-speed automatic, used in numerous Chrysler cars and trucks, has a stunning range: its first gear has a low 4.71:1 ratio, while its top gear is a high 0.67:1.  That automatic is the key to giving the V6 Charger its V8-speed acceleration, along with 31 mpg on the highway.

What will that transmission do for the top speed of the hottest Mopars?

The fastest four-seat Mopar 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 and Challenger beat that time?

The Charger Daytona’s drag coefficient was a stunning 0.28, a number that is still quite good over four decades later. 2014 Chargers and Challengers might not reach that level of slip, but with the supercharged HellCat engine and the superb gear range of the eight-speed automatic, they probably won’t need to.

With currently-used P245/45R20 tires and final drive ratio of 3.06, when the engine nears the current Hemi redline of 6,400 rpm (let’s say, when it’s at 6,200 rpm), various calculators claim the car should be going 208 mph, in theory. In reality, numerous factors get in the way, including wheel slip, aerodynamic drag, and such.

The eight speed automatic drops the top gear from 0.83 to 0.67, while raising first gear from 3.59 to 4.71. That means the SRT people can play around a lot more with axle ratios, and also puts seventh gear into play (for a ratio closer to the current Mercedes automatic’s top speed). In top gear, a Charger SRT8 with eight-speed and the same tires and axle ratio would be capable of 258 mph… in bench racing… with no wind resistance or other limiters… at 6,200 rpm. We do not expect the top speed to be 250 mph. 

We suspect that SRT is playing with axle ratios right now, trying to find the best way to maximize performance (there’s only so much traction at the rear tires); gas mileage could be left to take care of itself, helped out by the new automatic’s wide range.  Playing with the numbers, it looks as though the extra power from the Hellcat (rumored now at 550-620 hp) will push it over 200 mph.

Indeed, with the eight speed comfortably ensconced under the hood, even the “standard” 6.4 liter SRT cars might be able to beat the legendary Charger Daytona’s famed run.  We suspect the question will now change from “Will Dodge break its 44-year speed record?” to “Will it be Charger or Challenger that becomes the fastest four-seat Chrysler of all time?”   Discussion / forums

Update: 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.)  It looks like it’s going to require about 500 hp just push the Challenger through the air at 200 mph, using published drag and frontal area specs.  Factor in mechanical losses, rolling resistance, etc… and you’re easily well over 600 hp required at the crankshaft to do 200 mph Keep in mind that the 638HP ZR1 can only do 205 mph.”

The efficient ZF transmission may help SRT; an open question is whether HellCat will be in our conservative 550-620 hp range, or over 640 hp, as predicted by other outlets. The availability of a hefty overdrive in seventh gear may also help.


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