Short Take Road Test
The whole 392 thing was a total coincidence. So says Dodge Challenger chief engineer Tom McCarthy. In 2009, McCarthy and his team were discussing a punch-out of the Challenger SRT8’s rather peaky 6.1-liter V-8 for more midrange torque.
“I always thought that engine was tuned to the horsepower number,” says McCarthy, meaning that to reach the 425-hp benchmark engineers tuned the engine for revs to the detriment of usable torque. McCarthy and his team settled on giving the big-block a 0.9-mm increase in bore to 103.9 and a 3.6-mm stretch to the stroke to 94.5, for a total of 6410 cc.
These days, engineers work strictly in metric units, even at U.S. car companies. “I had no idea what the displacement worked out to in cubic inches,” claims McCarthy, until Dodge brand president and CEO Ralph Gilles casually asked in a meeting. Okay, math whizzes, it actually works out to 391.15 cubic inches, but that’s close enough for Chrysler to roll out the marketing war wagons. Way back in the late 1950s, hemi-head 392s powered the so-called forward-look Chryslers, including the fabulous 300 letter series, although it never was installed in a Dodge Challenger.
The 2011 Challenger SRT8 391.15, base price around $46,000 makes 470 hp at 6000 rpm and, perhaps more important, 470 lb-ft of torque, a gain of 50 lb-ft. The torque peak is lower, too, at 4200 rpm versus 4800 in the old 6.1. And, yes, the engine is still painted Hemi Orange.
It also moves the SRT8 to 60 mph in 4.5 seconds, 0.3 seconds quicker than the last SRT8 we tested, and through the quarter-mile in 12.9 seconds at 114 mph, almost a half-second quicker than the old mega-Challenger. (We only have test data on an automatic-equipped 6.1-liter SRT8, so the comparison isn’t totally apples-to-apples with this six-speed manual 392.)
Even quicker times might be possible outside of California, where the pumps only serve premium rated at 91 octane. McCarthy figures the car can improve by a tenth or two to 60. We shoved in a bottle of STP octane boost but have no way to determine how much effect it had until we can test the 392 back at our Ann Arbor headquarters.
Under the 2011 Challenger’s hood, plastic panels over the rocker covers scream the 392 moniker. While you’re poking around, you might notice that the intake rams are now plastic, too, instead of painted aluminum, as on the old 6.1. Cost was definitely a factor, says McCarthy, as was “tunability.” The plastic intake is a two-stage plenum with air flaps that effectively vary the intake ram length based on engine speed. In the block, the camshaft timing is now variable, stretching out the duration of the intake-valve opening for better cylinder filling. (No, it’s not the Viper’s fancy cam-within-a-cam system, so exhaust timing also changes during cam phasing.) The two systems work together to give the 6.4 much greater punch in the 2000-to-4000-rpm range where the 6.1 was somewhat wheezy.
Other engine enhancements include cylinder deactivation on automatic-equipped cars, a fuel-saving feature not offered on the old 6.1, and a rerouted intake that was heavily worked over by computational fluid dynamics software to be straighter and more efficient. Also, the compression ratio changes from 10.3:1 to 10.9:1. A straighter dual-exhaust system that ends in quad tips “just barely passes” the legal noise-level limit, says McCarthy.
Shockingly for a nation addicted to automatics, fully 50 percent of Challenger SRT8s are sold as manuals, according to McCarthy. The twin-disc clutch in front of the Tremec TR-6060 six-speed has been changed to accept the greater power, and the pistol-grip shifter’s throws are shorter. The rear differential internals are now shot-peened for extra strength.
Other changes for 2011 include new hydroelastic engine mounts—they suppress idle shake and better control the engine’s mass during cornering—stiffer suspension bushings complemented by larger front and rear anti-roll bars, a steering ratio quickened from 16.1:1 to 14.4:1, and an increase in the front negative camber from 0.8 degree to 1.4 degrees. We saw a very respectable 0.88 on the skidpad and a clipped 160-foot stopping distance from 70 mph. The tires, Goodyear Eagle F1 Supercars, remain the same summer-tire option as before, with all-season Goodyears also an option.
Inside, the steering wheel is one inch smaller in diameter than the old Challenger’s wagon wheel, and small detail enhancements such as a brushed-metal-look center console make the ambience less austere.
During some brief track work, the 6.4 roared lustily and pulled the big heavy Challenger up hills and out of corners strongly in third or fourth gear. The 6.4’s power still lives largest closer to the top end, but there’s more excitement in the midrange than ever before. And now the steering feels much more natural and lively, with a quicker turn-in.
Whether or not the displacement of the rejuvenated engine is a coincidence, the improvements to it and the car it powers were not only intentional, but very effective. You can see for yourself when the new SRT8 appears in dealerships later this month.
