600 Horses Take Wing
Edmunds Insideline | By Ken Field, Contributor
There are two places on the long track at Willow Springs International Raceway where you can clearly feel the difference between the 2008 Dodge Viper SRT10 ACR and any other Viper.
One is at the turn-in point of Turn 8, a fast right-hand sweeper that is entered at a very high speed, where a decent front-to-rear handling balance is necessary to swing the nose to the apex without losing the tail. The other is at the exit of Turn 2, where you come off the corner hard on the power to squirt down the short chute to Turn 3's tricky uphill left-hander.
In both of these places, the 2008 Dodge Viper SRT10 ACR feels noticeably better pinned to the asphalt than not only the current
Viper SRT10 but also any other Viper we've ever driven.
We're grateful. We can remember hammering that first 1992 Viper roadster down into Turn 8 at 120 mph all those years ago and it felt like an airplane crash in the making, as if it was going to take off and smash itself to pieces in the desert.
May the Downforce Be With YouThis improvement is not surprising given that the high-flying carbon-fiber rear wing unique to the ACR (American Club Racer) provides around 1,000 pounds of downforce at 150 mph, according to Dodge aerodynamics engineer Mike Shineling. Not only that, there's an equally prominent carbon-fiber front aero splitter that helps suck the nose downward, plus a full complement of various underbody aero kick-ups and fender-mounted aero dive planes.
The dive planes are said to account for more than 20 percent of the overall front downforce, generating aero vortices along the sides of the car to enhance air extraction through the wheelwells and help reduce turbulence.
A lot of midnight oil has been burned to get the ACR's setup just right. The SRT engineers used CFD (computational fluid dynamics) to help get the shape of the wing just right, and the Chrysler wind tunnel is in such huge demand for other vehicle projects that sometimes it is literally only available in the wee hours.
Enough Is EnoughObviously, aerodynamics played a big part in the ACR's development. And for a car with 600 horsepower on tap that's intended for track work in the hands of not only professional racers but also Viper club owners, it should. After all, power just takes care of the acceleration. Afterwards you still have traction and cornering grip to think about.
Of course, the standard-issue 2008 Viper also has 600 hp, and when we first heard that the 2008 Dodge Viper SRT10 ACR had an identical amount of power we were a little disappointed. Previous editions of the Viper ACR have offered a little more power than their more street-oriented siblings.
But Viper chief engineer Herb Helbig offers a reasonable explanation. "It costs the corporation millions to certify a new powertrain," he says. "And we'd just upgraded the engine significantly for all 2008 Vipers."
Besides, 600 hp is more than most drivers can exploit. So for the ACR, Dodge's SRT engineers have concentrated instead on weight reduction and high-speed handling, the very characteristics you'd expect from a vehicle intended to spend a lot of its time at the track.
Making It TurnWhen it came to trimming weight, the SRT team started with the wheels, the most beneficial place they could think of. By adopting two-piece StopTech brake rotors and using forged-alloy Sidewinder wheels, the team slashed 60 pounds at a stroke, and all of it in unsprung weight. (Of course 20 pounds have been added back to the car by the specific ACR aero bits.)
Then the SRT engineers went hunting for good suspension pieces, finding race-specification dampers from KW Suspension to be just about exactly what they had in mind. These shocks are 14-way adjustable in compression and rebound, and they permit ride-height adjustment as well, so the car can be lowered right down to 3 inches of ground clearance.
With spring rates that are about twice as firm as the standard Viper and a front antiroll bar some 20 percent stiffer, the ACR Viper rides pretty hard, yet it didn't feel too jarring to us at Willow Springs. Other than a couple of bumpy points on the track where the car would bounce slightly off course, the Viper circulated surprisingly smoothly. Despite a fairly serious lecture from chief engineer Helbig about not crashing, we discovered to our relief that this 600-hp car with a big racy wing is actually pretty easy to drive.
Now We Drive ItWe were suited up for track driving in fireproof gear and a helmet, and it took a bit of doing to squirm past this ACR's roll cage and buckle into the seat's five-point harness. Because so many owners of previous Viper ACRs have replaced the car's seat harness with their own preferred brand, Dodge has decided to supply the 2008 ACR model with the same three-point belts as in the standard street Viper. Don't fret; every Viper has mountings for a five-point harness anyway.
Once lashed in, we had the usual smallish wheel and tall center console to remind us what this car is about, so further orientation takes very little time. The 8.4-liter V10 pours torque down the tunnel at almost any rpm, so moving off from rest is easily managed. The new twin-plate clutch is not particularly heavy, and communicates its engagement point fairly well.
Out on the track, the ACR Viper comes into its own. The stiffer suspension feels better as the aero devices start to add downforce, and the lack of body motion helps you better assess the level of tire grip in corners. Michelin Pilot Sport Cup tires are unique to the ACR, with 30-series rubber all around on 18-inch front and 19-inch rear rims. The 295/30R18 front tires are 20mm wider, while the 345/30R19 rear tires remain the same. The tires grip with considerable tenacity, since they're blessed with a shallow tread pattern and contact patches the size of small farms.
The fluid supply of thrust from the V10 doesn't hurt, either. Although earlier examples of the Vipers have been known for the occasional episode of tail-happiness when you get on the gas, the ACR seems easy to read, and it can be booted out of corners with a long, linear surge of power without the threat of undue vehicular rotation. While you never want to mash the gas pedal in a strong car like this one, the ACR doesn't seem easily upset by big applications of throttle.
Rubber Side Down, PleaseSince we were trying to bear in mind Helbig's advice, we didn't really expect to take this track-tuned supercar to its ultimate limits. Even finding them in a car with this much aero assistance would prove an interesting exercise in technique (and bravery), but we were interested that Helbig insists the 2008 Dodge Viper SRT10 ACR is 2 seconds a lap quicker than its wingless stablemate.
Yet the ACR is still very much a Viper. Getting in means vaulting the wide sill and sinking down into the deep bucket seat. The shift lever is perched high on the tunnel, and requires a firm hand to guide it from gear to gear. The engine still has the unusual 10-cylinder growl and that surprisingly supple power delivery that completely understates its potential.
Once you're out on the track, the engine gets a serious, hard-edged tone to it as you wind it past 6,000 rpm, but it never feels over-stressed. It just gobbles one gear after another, effortlessly propelling the car to high speed. Six-hundred horses shouldn't feel this lazy, somehow, but it does, and you're glad the brakes are as strong as they are when you warp past your braking point.
$10,000 Per CylinderThe 2008 Dodge Viper SRT10 ACR's signature paint scheme is a two-tone treatment with a variety of special Viper colors complemented by a black center stripe. There's a Hard Core package for pure racers that deletes the audio system (replaced by a cover where you can mount the lap timer that comes with the package), the tire inflator, the underhood acoustic pad and the trunk carpeting to reduce overall weight by a further 40 pounds.
The bottom line is a price of $98,810, including delivery. While one could argue that the standard Viper offers all the power and pretty good dynamics for $12,050 less, it's clear that a track-ready 600-hp sports car at under a $100 grand is better than anybody else can manage right now.
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ACR's carefully shaped wing with end plates and a twisted chord adds 1,000 pounds of downforce. (Photo courtesy of Chrysler LLC)
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Air inlet in the hood is part of the standard '08 Viper, a measure to increase output to 600 hp. (Photo courtesy of Chrysler LLC)
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Wider front tires, aero dive planes and front aero splitter add more front grip while steering through the corners. (Photo courtesy of Chrysler LLC)
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Inside the cabin, there's a hand-sewn stripe on the leather-upholstered steering wheel; otherwise there's no difference between this Viper and an ACR. ( (Photo courtesy of Chrysler LLC)
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The shift action of the Viper's six-speed isn't slick, but you rarely miss a gear as long as you're not in a hurry. (Photo courtesy of Chrysler LLC)
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Deep-breathing 600-hp version of the 8.4-liter V10 is powerful enough for both this standard Viper and the ACR. (Photo courtesy of Chrysler LLC)
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Lightweight, forged-aluminum Sidewinder wheels conceal two-piece StopTech brake rotors. (Photo courtesy of Chrysler LLC)
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Front aero splitter incorporates three removable rub strips to forestall damage, and a center section can be added to increase downforce by 30 percent. (Photo courtesy of Chrysler LLC)
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KW suspension pieces feature adjustable compression and rebound damping plus spherical bearing mounts. (Photo courtesy of Chrysler LLC)
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ACR concept has its roots in the 1995 GTS-R, a racing car fielded at the 24 Hours of Le Mans by Oreca. (Photo courtesy of Chrysler LLC)
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First-generation 1999 ACR featured an upgraded engine with 460 hp. (Photo courtesy of Chrysler LLC)
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The ACR incorporates lessons learned by the Vipers competing in the SCCA Speed GT Championship. (Photo courtesy of Chrysler LLC)
