E = mc2. Anyone who has ever watched public television can recite this famous formula devined by Albert Einstein. It is seared into our brains, even if we don’t comprehend its full meaning.

What we know for certain is the equation quantifies something that previously seemed unquantifiable. And in that we find comfort because it appeals to humankind’s inherent compulsion to order the universe.

Now commit this to memory: 5.7L + 6MT.

It is the code for pure driving enjoyment. And it is revealed in the ’09 Dodge Challenger R/T.

In the muscle coupe’s mid-range trim, Chrysler marries two never-before-combined components – the new-generation 5.7L Hemi and the Tremec TR6060 6-speed manual transmission.

Churning together, their performance captures the basal elements of driving enjoyment. Responsive and exhilarating, the torque-rich V-8 and easy-shifting gearbox don’t just turn the Challenger into an extension of your right foot, they transform that appendage into a fearsome instrument of bona-fide butt-kicking.

Chrysler came close to this discovery with the limited-run ’08 Challenger SRT8. But its 5-speed automatic transmission seemed to choke the life from its monstrous 6.1L Hemi – despite the functionality afforded by the auto maker’s trademark Auto Stick shifter.

We haven’t felt frustration like that since BMW AG saddled the 5.0L V-10 in its ’06 M5 with the heartbreakingly balky Sequential Manual gearbox.

The vagaries of volume manufacturing forced Chrysler to let the 6060 sit on the shelf until now. The auto maker mused that introducing a new product and assembling it on the same line with platform-mates that don’t offer manual transmissions, the Chrysler 300 and Dodge Charger sedans, was an unnecessary risk.

The good news is it was worth the wait.

Optional on the R/T, the 6-speed gets the most out of Chrysler’s re-engineered 5.7L Hemi, generating 376 hp and peak torque of 410 lb.-ft. (556 Nm). Linked to the R/T’s standard-equipment 5-speed automatic transmission, the engine’s output is marginally lower at 372 hp and 401 lb.-ft. (544 Nm).

But – no surprise – the manual gearbox, available as part of a $995 pacakge, offers instantaneous access to effortless acceleration. The new Hemi, which benefits from a two-plug-per-cylinder ignition system, delivers power to the road with confidence-boosting precision.

The R/T’s electronic stability control, unlike the system on the more boisterous ’09 SRT8 with its 425-hp 6.1L Hemi, can’t be completely disabled. Call us Pollyannish, but we say get over it.

In the interest of science, we hammered the R/T’s throttle often. (Repeatability is the hallmark of successful experimentation.) And every tip-in was accompanied by some persuasive seat compression, immediately followed by a husky exhaust timbre so intoxicating it could redefine the parameters of V-8 sound. (Take note, Ford.)

The new Hemi, dubbed “Eagle” during its developmental phase, sings so sweetly you may never switch on the Challenger’s 7-speaker, 368-watt Boston Acoustics sound system. However, the tone emanating from the automatic-equipped R/T is slightly diminished.

Chrysler says its fuel-saving Multi-Displacement System, which periodically shuts down half of the Hemi’s eight cylinders, called for a tuning compromise to accommodate its two running conditions.

Engineers went toe-to-toe with designers over another feature of the Challenger’s exhaust. Designers wanted to see the car’s tips integrated in the rear molding, but engineers won out when they demanded a stand-alone configuration.

The result is a subtle nod to nostalgia on the Challenger’s updated lines.

’09 Dodge Challenger R/T
Vehicle type 5-passenger coupe
Engine 5.7L Hemi V-8; cast-iron block/aluminum head
Power (SAE net) 376 hp @ 5,150 rpm
Torque 410 lb.-ft. (556 Nm) @ 4,300 rpm
Compression ratio 10.5:1
Transmission 6-speed manual
Wheelbase 116 ins. (295 cm)
Overall length 197 ins. (502 cm)
Overall width 75.7 ins. (192 cm)
Overall height 57.1 ins. (145 cm)
Curb weight 4,041 lbs. (1,833 kg)
Base price $30,990
Fuel economy 15/23 mpg (15.6/10.2 L/100 km)
Competition Mustang GT, Mazda RX-8, Mitsubishi Eclipse
Pros Cons
Upgraded Hemi Pedestrian gauge cluster
Exquisite Exhaust Bulky seating
MT Had to wait for MT

Surviving from the nameplate’s glory days is the signature rear-quarter-panel bulge, which accentuates the sinewy crease that runs, stem to stern, just below its high beltline. The combined effect suggests both power and stamina.

A 3-piece taillamp that spans the width of the car says “back-off.” And its black grille sandwiched between a pair of round, dual-headlamp groupings is no less menacing – particularly the way it peers out from beneath a broad, chiseled hood highlighted by dual intakes that wear “Hemi” badges like a warning.

(From the Chrysler spin factory: Lift the Challenger’s hood and you’ll find a pair of circular depressions molded into a plastic surface that spans either side of the radiator. These, an engineer claims, are for holding celebratory beers back at the garage “after you dust off a Mustang.”)

The SE model, powered by a capable 250-hp 3.5L V-6, is plainer. But it retains the defiant, wide stance of its R/T and SRT8 siblings.

The cast-metal fuel door is another appropriate wink to the nameplate’s glory days.

The interior is less inspiring. The gauge cluster is parts-bin pedestrian and the front seats are bulky. And there is no rear-seat access from the driver’s side, a concession to the driver’s 8-way power-seat mechanism.

However, a high-mounted release on the front-passenger seat is accessible to the driver.

The SRT8’s high-backed, big-bolster seats hug nicely, while rear-seat legroom is surprisingly generous.

The R/T’s 4-spoke, leather-wrapped steering wheel features appropriate girth for managing the car’s prodigious pull. Feedback is uniform without inviting fatigue.

Front and center in the manual-equipped R/T is a leather-and-metallic-trimmed, pistol-grip shifter. Its smooth surfaces make for comfortable handling whether your preferred position is palm-down or revolver-style.

The stick’s forgiving throw seems to welcome aggressive slamming as readily as it accommodates the relaxed shifting required of rush-hour traffic.

Pedal feel affords the desired connectedness, particularly the clutch, which is so pliable it begs you to rev the new Hemi.

While the ’09 SRT8 can be had with the Tremec transmission, and it boasts nearly 70 hp/L, Chrysler’s highest-ever specific output for a naturally aspirated V-8, it also comes with a heftier price tag.

With the 6-speed, the SRT8 starts at $42,390. But the R/T starts at $30,990. That’s a difference of $18 per pony – a winning formula if ever there was one.

emayne@wardsauto.com