Specialty File
The roar of the Hennessey-massaged Hemi fills the Dodge Magnum interior with frantic, hard-edged V-8 surround sound at the same time it trumpets its baritone song to any bystanders within earshot. The heavy-metal exhaust note is remarkable - literally remarkable - because when I stop, our photographer, David Dewhurst, is suddenly at the window waxing lyrical about it. We begin to wish we'd brought digital recording gear so we could put this stuff on www.CARandDRIVER.com.
That big voice emanates from an equally big 6.1-liter Hemi ripping up and down a pretty dusty airstrip in Southern California, recording acceleration runs with angry blasts of sound and energy. Traction is an issue here, so we're leaving on the Electronic Stability Program (ESP). It seems to be happy allowing both rear tires to spin at the same speed, and refrains from chopping the power. But we aren't entirely happy about it because the big BFGoodrich 295s on 11-inch-wide, three-piece wheels have a problem hooking up under the aggression of 520 horses.
You have to tip into the throttle progressively to get the car rolling, transferring the weight to the rear end, then go to full throttle when it feels like Mr. Goodrich has a grip on things. Even then, the power builds so suddenly it can snap those hoops loose and turn your ET into acrid tire smoke. So what else is new? With the horde of 500-plus-hp megacars streaming into the market these days, we test drivers live in search of traction.
This dusty strip is not ideal, but the Hennessey Magnum still clocks 12.9 seconds and 114 mph as it breaks through the quarter-mile. That's 0.7 second and 8 mph quicker than the already-fast SRT8 Magnum we tested in September 2005, and it doesn't quit there. The SRT500 reaches 130 mph 4.8 seconds before the stock car does and feels every bit that strong. The top-end thrust is intense and exhilarating, and the wagon pulls hard enough to trigger ESP intervention even at high speed as it encounters pavement seams and cracks. Clearly, there is more to be had here if we could just find some grip. But, hey, this is Southern California, where test facilities are few and far between, and where the winter season has been accompanied by high winds and plenty of dust.
Perhaps we should have gone to Houston, Texas, where John Hennessey builds his tuner cars. That's where the development work was done on the 6.1-liter Hemi's cylinder head, porting and polishing the various orifices. Intake-port flow, for example, increased from 300 to 345 cubic feet a minute. The compression ratio was bumped a tick higher to 10.5:1, and the valve retainers were replaced with titanium units.
To increase intake airflow, Hennessey employs a cold-air-induction system (available separately for $450). To provide exhaust gases with a similarly easy passage, the car wears a dual stainless-steel MagnaFlow exhaust system and 1.9-inch stainless-steel headers. The engine modifications add up to $9950, including installation, but the stainless header tubes are optional extras, said to provide an additional 20 horsepower, and they run another $2950.
You could stop right there and have a big-horsepower Dodge Magnum (or Charger, or 300C, or Grand Cherokee, or anything with the 5.7 or 6.1 Hemi) for about $13,000. But then you'd have to forgo the adjustable KW Variant 2 coil-over suspension kit that ties the car down just that bit tighter than the stock setup and drops the ride height 1.5 inches in front and an inch and a quarter in the rear. You'd save $2795 right there.
You'd also have to run the stock SRT8 wheels, too, and miss out on Hennessey's 20-inch Venom 6R three-piece wheels and the BFGoodrich KDW2 tires that set the SRT500 apart from the dealer's car. (The wheels are $4950, the tires $1650, mounted and balanced.) Would that really matter? In our view, not much. The car we drove recorded a slightly lower lateral-acceleration number than did the stock Magnum SRT8 we tested last fall (0.85 g versus 0.87) and took slightly longer to stop from 70 mph, too (174 feet versus 170).
Given the dusty conditions, we'd say the Hennessey car would likely improve slightly on both of those numbers in a stickier environment. But the original SRT8 is not short of dynamic potential as it comes. John Hennessey chose not to replace the stock vehicle's Brembo brakes, and that's a measure of how well the SRT8's chassis was sorted for the stock 425-hp drivetrain.
Still, if you're going to drop a wad of cash on your new baby to endow it with more than 500 horsepower, why stop there? If the $37,995 SRT8's 425 horsepower isn't enough for you, then the stock suspension and 20-inch wheels aren't likely to be, either. Besides, other than producing some rubbing noise in hard right turns, the upgraded suspension and lower ride height didn't seem to hurt the overall ride character too much. A short drive on mainly smooth surfaces suggested the SRT500 would retain a fair degree of everyday civility when on domestic duty.
The accurate and deliberately weighted steering felt as good as ever, and body motions were well snubbed. As usual with the SRT versions, the big wagon felt as wieldy and responsive as a much smaller car might. It would take some time to gauge just how much throttle one could exploit at corner exits, but until then it might be wise to have the ESP act as co-pilot.
As we expected, Dodge's five-speed automatic has adapted to the pumped-up engine as if nothing had changed. Shifts were fast and positive, and kickdown response summoned big gobs of torque in lower gears with the same seamless action you'd anticipate from the stock vehicle. As long as the new power doesn't outstrip the transmission's torque limit, that's how it should be.
What's particularly appealing about Hennessey's SRT500 conversion is that it's simply an amplification of what was great about the 6.1 Hemi in the first place. Nothing feels and sounds quite like a brawny, naturally aspirated V-8 breathing through nice wide pipes. And we can't think of a better covert hot rod than a Magnum, with its chopped greenhouse and pugnacious front end.
Then there's that sound. Hear it once, and you'll reach for your checkbook.
Hennessey Performance Engineering, 11513 North Petropark Drive, Houston, Texas 77041; 713-466-3420; www.hennesseyperformance.com.
