IRS Leads the Way, But Will True Enthusiasts Follow?
John Clor, Contributor
Based on our experience driving the SVT Mustang Cobra the past few years, we must admit to being fairly excited when we found out that Ford's Special Vehicle Team was adding an honest-to-goodness independent rear suspension to the Cobra for 1999. Indeed, a brief track stint in the '99 was enough to land it on Edmunds.com's "Most Wanted" list as our staff's pick for the most desirable sport coupe in the $25,000 to $40,000 category.
We've long noted SVT's Cobra ranks high in the fun-to-drive class. But its performance credentials aside, the fact that Ford's hottest factory Mustang has always been saddled with the limited handling ability of a live rear axle hasn't been lost on our staff's enthusiast-types. And we're certainly not the only ones who found that the beam axle setup was quick to bare the Cobra's pony-car roots when driven at the limit. So it's easy to see why the new chassis layout was much-anticipated by Ford friends and foes alike.
The idea of giving the high-performance version of America's favorite pony car the ability to plant its rear hooves independently, rather than through a solid axle, has been kicking around for some time. In fact, John Plant -- who as SVT's first leader helped put the Ford performance group on the corporate map -- always bemoaned the fact that SVT's Mustang, beginning with the 1993 Cobra, didn't have IRS. Up until the day he retired and turned SVT's reigns over to more marketing-driven leadership in 1995, Plant would tell the team that the Fox chassis-based Cobra would never be embraced by real driving enthusiasts until it loses "that damn stagecoach rear axle."
Well, more than six years and some 50,000 SVT Mustang Cobras later, he finally has his car. "It took a while, but the folks at Team Mustang finally listened," we proclaimed in our "Most Wanted" segment. "The 1999 SVT Cobra is not only the first-ever Mustang to leave the factory with a true independent rear suspension, but it also packs 320 horses to boot." And while the new Cobra's IRS has helped to put it at the top of our list this year, an issue concerning the power boost -- from the 305 horses it's had since '96 to 320 for '99 -- has kept it off our road-test schedule until now.
That's because some new Cobras were found NOT to be making the 320 horsepower they are advertised as having. After a wave of owner complaints caused a stir, Mustang engineers were forced to spend much of the summer investigating possible reasons for the less-than-potent '99 motors, and how to remedy the situation. Meanwhile, in an effort to get a grip on the problem, SVT slapped a temporary hold on retail delivery of the remaining '99 Cobras left in dealer stock until they can all be inspected and fixed.
SVT eventually told its dealers a special service program involving reworked intake manifolds, mufflers and engine computers should bring the engine back up to specs, but that it will take the company some time to come up with the parts. Ford isn't saying how many of the more than 8,000 SVT Cobras produced for the 1999 model year may be afflicted with the condition, but at this writing SVT dealers are in the process of contacting owners about the problem. If you own a 1999 SVT Mustang Cobra and are not yet aware of this issue, you owe it to yourself to contact your SVT-certified Ford dealer or call the SVT Information Center at 1-800-FORD-SVT for more details.
All this hubbub over the engine's power output has meant a freeze on all press vehicle loans of '99 Cobras since the end of May -- precisely when our scheduled road test of a Cobra Coupe was abruptly cancelled. But while pulling the cars from press-fleet duty kept the new Cobra from participating in Edmunds.com's Muscle Car Comparison Test this summer, it didn't stop our editors from road-testing one. After all, there's more than one way to skin a snake.
We were lucky enough to persuade the proud owner of a 1999 SVT Mustang Cobra Convertible to loan us her car for this road test. The deal was we could drive the car for the day if we didn't: 1) perform any instrumented testing, 2) abuse her car in any way, or 3) reveal her name or license plate number on the Internet. We agreed to all of the above, and took off with her car for an afternoon of driving in the countryside north of Detroit.
Our "test-car-donor owner" had ordered her new Cobra Convertible at a Detroit-area dealer and was happy to pay sticker for it. She could have chosen Ebony Clearcoat, Rio Red Tinted Clearcoat or Electric Green Clearcoat Metallic, but settled on Crystal White Clearcoat paint with a Medium Parchment leather interior and matching top. (The only other interior color choice is Dark Charcoal.)
She said she ordered the Cobra's only option, which is a rear decklid spoiler, because she thought it made the car "look sportier." But SVT takes care of providing its own "power dome" hood, front fascia with round fog lamps, unique side cladding and rear fascia, special tri-color taillamps and "SVT Cobra" badging -- all to help set this limited-run snake apart from the pack.
Of course, the primary reason for buying the SVT Mustang is for its performance hardware. For 1999, that includes the aforementioned IRS unit and the revised DOHC, 32-valve 4.6-liter V8 found only in the Cobra that, hopefully or eventually will make 320 horses and 317 foot-pounds of torque. This motor is one of very few in the world that is hand-assembled, which takes place on a dedicated "Niche Line" at Ford's Romeo (Mich.) Engine Plant. It features an aluminum block and heads, forged steel crankshaft, water-to-oil engine cooler, chain-driven cams with roller-finger followers, a 57mm twin-bore throttle body and an 80mm diameter mass-air sensor. Cast-iron exhaust manifolds send spent gases through a 2.25-inch-diameter stainless-steel dual exhaust system that terminates into twin, 3.0-inch polished rear tips.
The '99 engine has shed its old "butterfly port" intake system for a new "tumble port" cylinder head design that makes the fuel/air mixture entering the combustion chamber tumble inward instead of swirl around the cylinders. In case that sounds too abstract, consider the explanation we heard one scribe deliver: "Picture the difference between a pitcher of beer being poured (the tumble) and a toilet bowl flushing (the swirl)." In any event, the tumbling action was designed to improve both volumetric efficiency and performance.
This year's motor also got higher-lift, longer-duration camshafts with bigger valves and a new coil-on-plug ignition system that not only makes a higher-energy spark, but is more reliable than the previous dual-coil system. Redline is way up at 6,800 rpm, with fuel shut-off taking place at 7,000 revs.
The Cobra's only transmission choice remains the Borg-Warner-designed T45 built by Tremec. New this year is a larger, 11-inch clutch plate with revised pedal action for shorter travel. Power is sent to the rear wheels via a limited-slip aluminum differential with a 3:27 axle ratio. Ford had estimated a zero-to-60 time of around five and a half seconds, and a quarter-mile being covered in 13.8 seconds with a trap speed of 102 mph. In closed-course testing, Ford engineers drove the Cobra to a top speed of 150 mph. Of course, these numbers were reportedly realized with a Cobra prototype that was tested to turn out an honest 320 horses. We hope your results won't vary.
Of course, SVT has long preached that there's much more to a performance car than mere horsepower. So it also adds its trademark uplevel, power-assisted four-wheel disc brakes with twin-piston PBR calipers and new-for-'99 13-inch Brembo vented front rotors. Single-piston calipers put the pinch on a set of 11.65-inch rotors out back.
New 17x8-inch forged alloy wheels have exposed lugs and are again available only with a silver-painted surface. Ford must want to keep making the aftermarket wheel suppliers rich by refusing to offer chrome wheels on the Cobra. That decision is not only a stupid marketing blunder, but also a shame for the buyer -- who often feels compelled to spend more money (money he can't finance with his car loan) to upgrade his ride with some proper chrome rims. Factory rubber is a set of 245/45ZR-17 BFGoodrich Comp T/As.
Standard for the '99 Cobra is Mustang's new, all-speed traction-control system, complete with an on/off switch in case you feel the need to do a smoky burnout or two. The Bosch system is linked with the ABS and engine control computers; when rear wheelspin is detected, the system can retard ignition timing, shut down spark and fuel to the cylinders or simply apply the brakes at one or both driven wheels to bring the car under control.
Inside things remain pretty much the same, except the power driver's seat now has a six-way adjustment (last year's was only a four-way), and an inch of rearward travel has been added to its track for a scootch more room for taller drivers. Again this year, SVT-signature white-faced gauges and a tilt, leather-trimmed steering wheel are standard. So are a defroster for the rear window (which is real glass on the ragtop), power windows, mirrors, door locks and trunk release, as well as a leather shift knob and boot. You also get dual illuminated visor mirrors, front floor mats and remote keyless illuminated entry included. To keep would-be thieves at bay, Ford throws in its highly successful SecuriLock passive anti-theft system with encoded ignition key. To top it all off, Mustang's top-of-the line Mach 460 sound system, with electronic AM/FM stereo cassette and CD player, is also included on the Cobra.
If that sounds like a lot of equipment for your basic, high-performance $32K droptop, well, you're right. A comparably equipped, uplevel Chevy Camaro SS Convertible costs roughly $2,000 more, and the top Pontiac Firebird Trans Am Ram Air ragtop stickers at more than $37,000! When buff-book road testers start talking about the "bang for the buck" being offered by GM's F-body cars, you might do well to skip past the base MSRP and look right over at the "as-tested" price. Performance value, however, is quite another story, so we were eager to head out on the highway to test out the Cobra's new IRS.
First we must tell you that once we left the interstate and got the chance to wind out the Cobra on an open stretch of two-lane, we could tell immediately in the seat of our pants that this particular '99 Cobra indeed felt slower than last year's car. We're certain that the previous engine's butterfly port-throttle system delivered more power lower in the rev range, which helped bring the motor "on-cam" a little sooner.
This new "tumble port" motor felt as if it builds power gradually down low, then begins steamrolling once the revs soar past 4500 or so. There was more than enough power to easily spin the tires on takeoff, though we did notice a hint of rear wheel-hop during one hard launch, which isn't likely to make drag racers too happy. But we had promised not to abuse this car, so we decided to save the quarter-mile sprints for a time when we bring out the test equipment. Once we were satisfied we had a bead on engine performance, we headed off to a very bumpy section of road that we knew would put the Cobra's new IRS to the test.
So why should even non-enthusiasts be interested in driving a car with IRS over a tried-and-true live axle? Well, simply put, IRS allows the rear wheels to work independently of one another. That helps keep both rear tires in full contact with the road more often, especially on bumpy or uneven surfaces, which means a better ride. The performance logic is, the better the tire contact, the better the car can put power down to the road to accelerate or to provide better lateral grip during cornering.
With a traditional beam axle, anything that the right wheel is doing is immediately transferred over to the left wheel, and vice versa. Smack a bump or pothole, and wham -- the whole unit is dancing all over the place, moving the back end of the car laterally and leaving the front to try and stay on the pavement. Another advantage of IRS is that it also reduces rear lift under braking, especially while turning. And by offering more usable rear-suspension travel, there's less bottoming-out on those really big bumps in the road.
One neat thing about the Cobra's IRS system is that it is delivered to the factory pre-assembled on its own isolated tubular subframe, ready to bolt right into the Cobra. The attachment points are exactly the same as those used for the live axle with links on the 1999 Mustang V6 and GT. (Yep, that means the IRS unit can be bolted into any SN95 Mustang. While there's no official word on availability, we'd expect swap kits to be ready for sale by the time next year's SVO race parts catalog come out.) About the only thing that Dearborn Assembly workers do differently to install the IRS is to use a slightly rerouted exhaust pipe to get around the new suspension and mount the ABS sensors inboard on the Cobra half-shafts instead of outboard, like on the GT.
Ford engineers said the IRS unit weighs some 80 pounds more than the old live axle, but after they put the Cobra on a diet to lose about 30 pounds from the front end and 20 from its midsection, they nearly made up for the added heft of the IRS. But the good news is that the IRS reduces the Cobra's unsprung weight -- the parts of car that are not controlled by its springs and shocks -- by 125 pounds. What's more, shifting some of the car's weight to the rear makes for better overall handling, braking and traction. An IRS Cobra carries a 55/45 percent front/rear weight bias, while the GT's is a more nose-heavy 57/43 percent.
The Cobra's front suspension remains a modified MacPherson-strut design, with lower control arms, linear-rate springs and a 28mm stabilizer bar. For '99, ride height has been lowered by about a quarter of an inch, with the geometry tweaked and the steering rack modified to reduce the Mustang's turning circle by a total of three feet. Ford also revamped the steering's hydraulically assisted boost curve and tie rods to enhance feedback and deliver a better on-center feel. For us, the steering improvements made themselves evident in a single pass over some challenging pavement.
But let's face it, Ford's work on the front suspension is bound to get overlooked with the addition of IRS. Next time you're in a Ford SVT showroom, just crawl underneath the nearest Cobra and take a good look at its nifty IRS unit. The system consists of steel upper control arms and aluminum lower control arms with aluminum spindles. You'll notice that fixed tie rods are placed behind the center of each wheel to control toe characteristics during cornering. Linear-rate coil springs and a 26mm stabilizer bar complete the setup. It's all nice and tidy, and looks like it came off an exotic sports car.
By now, it was finally time to pilot our borrowed Cobra over one particularly neglected piece of broken-up pavement that we found in the far reaches of Southeastern Michigan's St. Clair County. We made several passes over this deserted stretch of road at varying speeds, not bothering to avoid all the crumbling and cracked sections of tarmac in the hope we'd upset the composure of the IRS. After about a half-hour of aggressive driving, we must admit that we came away very impressed with the ability of this unit to absorb bumps and keep any bump-steer to a minimum.
Next, we headed over to a twisty little road that, although quite smooth, offered several tricky undulations as well as some off-camber turns. Again, we attacked the road at a good clip for more than a half-hour, and again we came away impressed at how the IRS keeps the Cobra more connected, more controlled as you approach its handling limits. One of the first things you notice is how strangely quiet the whole thing works, with very little road noise being transferred into the car. With its lateral movement in check, initial turn-in is sharper and the feeling of understeer is significantly lessened.
After another hour or so of scouting around for some photo locations and snapping off a few pictures for you to enjoy, it was finally time to point the Cobra back toward Detroit and return it to its anxious owner. We had heard some Cobra owners complain of their new IRS units clunking or squeaking, but ours ran smooth and quiet. We had also heard that a big problem surfacing with some of these cars is supposedly a vibration in the driveshaft at highway speeds. So on the way back home, we experimented with keeping the Cobra at a constant speed of about 70 mph to check for vibrations. But we could find no such problem with this car.
Upon our arrival at the owner's home in Detroit's far-eastern suburbs, we were asked many questions. We stood and watched as the Cobra's owner (and her father) carefully inspected every inch of her car for damage. Nary a stone chip. As a token of appreciation, we gave her an Edmunds.com key chain, as well as a nice, new SVT hat and a Cobra poster that the gang at SVT had sent us. We all walked away winners.
Overall, we found the IRS has truly elevated the Cobra from pony car to, well almost a sports car. It would still have to lose the front struts in favor of an SLA or wishbone-style independent front suspension to make it all the way up to the sports-car category. And it would also have to lose those black plastic inserts in its hood and flanks in favor of some functional fresh-air intakes to make real enthusiasts take notice.
We understand that next year, Ford plans to introduce another of its trick color-shift paints for the SVT Cobra, much like the special run of 2000 "Mystic" Coupes back in '96. This time around, the refractive paint is expected to be a gold color that shifts to an orangey-red when the light hits it just so. But the current build problems are delaying SVT's announcement of a Job One date and specifics for the '00 model.
Based on our day with the 1999 SVT Mustang Cobra, we think Ford would be better off spending time and effort improving the quality of its flagship performance car than worrying about fancy paint. People who buy these cars tell us they want top-grade hardware and materials that are screwed together well and provide segment-leading performance. What they don't want is underachieving engines, quirky service problems, fake scoops and marketing hype.
The addition of IRS is surely a step in the right direction. But now seems like the perfect time to give SVT's go-fast guys, Special Vehicle Engineering, a greater hand in Cobra's development. Then maybe we can get class-leading horsepower from the Cobra's 4.6-liter, or better still, shoehorn the Lightning pickup's supercharged 5.4-liter motor into the SVT Mustang. And hey, let's just see if they could make those scoops functional while they're at it!
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