Second: Venom 1000 Twin Turbo

Power (C/D est): 1033 bhp @ 5500 rpm

Torque (C/D est): 1096 lb-ft @ 4700 rpm

Street drivability: 4 stars

Zero to 200 mph: 22.0 sec

¼-mile: 11.1 sec @ 145 mph

200-to-0-mph braking: 1127 feet

Total time, 0 to 200 to 0 mph: 30.7 sec

John Hennessey is well-known to readers of Car and Driver for his tuning exploits with Mopar products, so it was a no-brainer to invite him to our inaugural 0-to-200-to-0 challenge with his 2006 Venom 1000 Twin Turbo, née Dodge Viper SRT10.

Outwardly, the Venom looks like a fairly regular Viper -- save for an enormous rear wing that was removed for running at Wurtsmith -- but under the composite paneling, it has been highly modified. The V-10 engine is bored and stroked to give a capacity of 513 cubic inches, up from the stock 506. This involves new pistons, connecting rods, and ported cylinder heads, and a laundry list of other hardware changes. The fuel system is also upgraded, with larger injectors, new lines, and a more powerful pump.

Turbocharging SRT engines is a Hennessey trademark, so it's no surprise to find twin Garrett ball-bearing turbos with a liquid-to-air intercooler at the front of the engine bay. An AEM system modifies the boost progressively from a base level of 9.0 psi to 14.0 psi (on pump gas) when the Venom gets into fourth gear.

All the mods seem to work, as evidenced by a stout 878 horsepower and 932 pound-feet of torque on the chassis dyno. Those numbers match up as our calculations yielded 1033 horsepower and 1096 pound-feet at the flywheel, which is a bit above the 1000 horses Hennessey advertises. As someone quipped, "You could power a small city with that engine."

To cope with all the grunt, Hennessey fits a Centerforce ceramic-and-metallic single-plate clutch and heat-treats the gears in the Viper's stock Tremec T56 six-speed manual transmission. The back axle has a Quaife limited-slip differential and a stock 3.07:1 ring and pinion.

On this car, which has run One Lap of America, the suspension is massaged. The spring rates are roughly 10 percent stiffer up front and 20 percent higher out back. Plus, Moton dampers that have remote reservoirs are bolted on. Factory brake calipers remain in place, cozying up to StopTech 14.0-inch vented rotors, with Pagid carbon-metallic street-and-race pads. The price of all these performance modifications more than doubles the cost of a Viper coupe, to $178,145.

Out on the street, the Venom feels, well, like a Viper. The ride is a little firmer than a stock machine's, and there's some driveline and valvetrain clatter, but otherwise it's remarkably civilized -- there are no low-rev tantrums, no grabby clutch, no balky shifter. The exhaust note is a bit louder than a stock Viper's, and the competition-style brake pads are a touch grabby, but it's hard to believe this car is making somewhere around 1000 horsepower. Until, of course, you put your foot into the gas pedal, and the Venom spears toward the horizon. In the damp conditions on our drive from Ann Arbor to Oscoda, discretion was definitely the better part of valor.

Unfortunately for Hennessey and his team, it all went south in northern Michigan. Driver Sriyantha Weerasuria saw wheelspin in first through third gears on his initial run, hitting the quarter-mile in 11.1 seconds at 145 mph on his way to 200 mph in 22.0 seconds. The 0-to-200-to-0 run took 30.7 seconds, including a hairy moment when the Venom caught a gust of wind at 190 mph.

Weerasuria's second run started well with a nearly perfect launch, leading to a quarter-mile in 10.8 seconds at 151 mph. But then "it felt lazy when I got into fifth gear," he reported. A head gasket had blown. Game over.

First: Heffner Ford GT1000TT

Power (C/D est): 1098 bhp @ 6600 rpm

Torque (C/D est): 911 lb-ft @ 5900 rpm

Street drivability: 4 stars

Zero to 200 mph: 18.9 sec

¼-mile: 10.6 sec @ 152 mph

0 to 200 to 0 mph braking: 1089 feet

Total time, 0 to 200 to 0 mph: 26.5 sec

Jason Heffner is an engagingly intense 30-year-old Florida-based tuner whose priorities are well conceived to please his clients. Like anyone in the expensive business of bolting more power into an already potent car, he wants tangible results. But he also wants those results to be repeatable, time after time, with none of the fragility that afflicts some tuner specials.

To this end, Heffner is particularly fond of the engine in the stock Ford GT.

"The Ford guys really did their homework," he said. "It's pretty rare for us to take something apart and decide it doesn't really need improvement."

Heffner added that he and his crew did hone this GT's cylinder bores and "loosen up the tolerances a little," but he wasn't at all sure there was any benefit. "We've done 10 of these cars now, and this is the only one where we've done any work inside the engine. I wouldn't recommend it to anyone else, because there's no real gain."

Beyond those minor mods, the word "stock" occurs frequently in reference to the internal organs of the GT's 5.4-liter V-8: stock crank, stock rods, stock pistons, stock clutch, stock transaxle, and stock gear ratios.

But the hardware that makes the GT capable of 218.1 mph in the standing-start mile is far from stock. Heffner substituted a pair of Garrett GT35R turbos for the GT's supercharger, with max boost set at 18.0 psi. He retained the stock liquid-to-air intercooler -- "We would have had to relocate the intercooler to do air to air" -- but doubled the coolant capacity from one to two gallons.

The package also has 70mm throttle bodies, a Heffner-developed intake manifold, advanced intake-cam timing, retarded exhaust cams, free-flow mufflers, and three-inch exhaust plumbing. All the foregoing added up to 933 rear-wheel horsepower on the Wheel to Wheel chassis dyno. Figuring a 15-percent power loss from the crankshaft to the rear tires, the twin-turbo GT was churning up 1098 horsepower, almost double the output of the stock engine.

For street use, the GT1000TT wears a set of fat Pirellis -- front 255/30ZR-20 P Zeros and rear 335/25ZR-22 P Zero Scorpions. For the speed runs, Heffner bolted on a set of sticky Hoosier A6 autocross tires -- 245/40ZR-18 in front, 315/40ZR-19 at the rear. With drag racer Gary Javo from Savannah, Georgia, at the helm, the GT clocked the quarter-mile in 10.6 seconds at 152 mph and hit 200 mph in 18.9 seconds. For contrast, the last Ford GT we tested ["Lords of Envy," August 2005] did the quarter in 12.0 seconds at 123 mph and needed 19.1 seconds to reach 150 mph. Wow.

Combined with a set of Ford Racing brake rotors, the Hoosiers also paid off in the test's shortest stop: 200 to 0 in 1089 feet, which in turn added up to the best 0-to-200-to-0 result: 4642 feet in 26.5 seconds.

Considering its face-distorting thrust, the Heffner GT is remarkably docile on the street. A set of Eibach springs and Penske adjustable shocks raise the roll stiffness, but the ride quality is civilized nonetheless, the clutch is agreeable, and drivability is of the everyday variety. Owner Ray Hoffman, a Texan who had barely taken delivery of the finished car by test time, called it "a sweetheart." We have no argument with that label.

So what does this sweetheart cost? Heffner's tweaks added a little more than $50,000 to the price of Hoffman's GT, most of that -- $40,000 -- going where it's easiest to appreciate: the engine.

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