Rich and Jean's Lime Rock 3-way examination of race cars versus road cars.
This all started when Eric Morrow invited me to come track-test a Bill Mitchell-prepared Mustang GT race car he was planning to buy for the SCCA's American Sedan class. Then car builder Bill Mitchell, of SVD (Special Vehicle Developments) in Cheshire CT, volunteered to bring not only the AS Mustang but also a Mustang Cobra R he'd prepared for the SCCA's much more aggressive World Challenge series.
This World Challenge Mustang was the very same car in which Boris Said III won the 1996 Lime Rock World Challenge race, an absolutely state-of-the-art entry in this highly-competitive series. Throw in our long-term Mustang Cobra as a baseline, and suddenly you had an interesting day's work.
And so it was. We met at Lime Rock one Tuesday afternoon to ride these three similar but very different horses. Morrow and I ran multiple 10-lap sessions in each of the three cars, Jean handled the cameras, and Bill Mitchell juggled the stopwatches. Between sessions we debriefed into the tape recorder, getting our impressions down while they were still vivid.
Cobra R World Challenge
Eric and I both fell in love-what an incredibly well-developed race car! I felt like I could drive the Mustang anywhere on the track; the line didn't really matter. Mitchell's mods give the car a trustworthy feeling from the very first corner, and that trust was never once misplaced. The brakes, handling, and power were all superbly balanced, giving the World Challenge driver god-like confidence on the track.
Within five laps I was turning times under the magic 1-minute mark, the traditional dividing line between fast and really fast production-based cars at Lime Rock. In our short sessions, Eric and I both got within a second or so of Said's 58-second record lap in the car, and we both came away swearing we could whittle another fraction off given more practice.
Our reactions were typical of our personalities-I said, "Nice to know I haven't lost it. I can still get close to a guy like Boris!"
Eric said, "This car's so good, it even makes two amateurs look like a couple of pros!" My ego would like to think that both of us were right, but deep down I'd have to side with Eric.
Starting with one of the 250 1995 Mustang Cobra Rs-the only modern Mustangs built with Ford's 351-cid V8-Mitchell's crew turned it into a world-beater by making only small changes. Insignificant changes. Honest. They started by gutting the car and then back-filling the cockpit with an elaborate rollcage. The SCCA's World Challenge rulebook prohibits a tube-frame chassis, so by the book this is still a modified production car dependent on the original unibody for its strength. Does the rollcage help? Well, it couldn't hurt....
The stock Cobra R we tested in our July '95 issue weighed 3326 pounds; Mitchell's World Challenge car weighs 2825. Trust me, it isn't easy to shave 500 pounds off a modern production car, particularly when 150 additional pounds of rollcage and on-board fire-suppression hardware are mandatory. Every power accessory, all the insulation and padding, and every bit of cosmetic trim has been stripped and replaced by a solo racing seat, a padded wheel, and a dash full of racing gauges. A 22-gallon fuel cell replaces the stock gas tank.
According to the rules, Mitchell can tweak the 351 Windsor V8 with off-the-shelf GT40-type aluminum heads, internal polishing and balancing, and less restrictive exhausts. Within that framework, the 1995 Cobra R's quoted 300 bhp has been boosted to 420 and torque goes up from 365 lbs.-ft. to 460. There's no secret about the result; if you remove 500 pounds and add 120 horses, you're going to get a quicker car.
Mitchell also replaced the production car's 5-speed Tremec with a stronger, lighter 4-speed Jerico gearbox. At rest the Jerico puts up a fight when you try to select first, but once underway it snicks in and out of gear with nary a graunch. Interestingly, even at a tight little track like Lime Rock, Mitchell runs stock 3:23 gears in the diff. For brakes, SVD uses Brembo calipers on stock Cobra 13-inch vented discs up front and Corvette calipers on stock 11.7-inch vented discs out back. With racing pads, these new calipers transform an okay stopper into an eyeball-sucker.
Bill Mitchell started out decades ago as a suspension engineer at General Motors, and handling is still his forte. In the rear, he has replaced the stock Mustang's 4-bar live-axle suspension with what he describes as torque arms and a Panhard rod. Under World Challenge rules, Bill was also allowed to remove the entire MacPherson-strut front suspension and replace it with a set of double wishbones with coil-over spring/shock units, so SVD has fabricated just such a setup in its shop. The new front end lowers the car a lot, and it has proper camber curves matched to the super-sticky 275/40ZR17 Goodyear tires.
The World Challenge entry is fairly close to stock as far as race cars go, yet almost every factory component has been replaced, modified, or removed. None of this is cheap. Our test car costs about $75,000, including the $35,000 MSRP of the original 351-inch Cobra. Still, for a car that can make me look like Boris Said III, it's a bargain.
When I suggested to Morrow that he buy the World Challenge Cobra and hire me to drive it in the series, Eric flashed me the same look that Darth Vader would give an incompetent underling. Aside from the fact that he'd rather do his own driving, Morrow and Mitchell patiently explained that to run a coast-to-coast series like World Challenge requires at least $300,000 for travel, maintenance, and all the other incidentals that make professional racing, well, professional. The $75,000 car is just the tip of the iceberg.
Mustang GT American Sedan
Interestingly enough, Eric and I both hated the Mustang he'd come to buy. In fact, we hated the AS version as much as we loved the World Challenge car.
What could possibly be so different? Well, the whole feel of the thing. Within ten laps we were both able to run 1:01-1:02s, but we were also both very uncomfortable. Eric laps this track at one minute flat in his current AS car-a Camaro built by Mitchell two years ago-so the Mustang, at least as it sits, would be a major step back.
Essentially, the American Sedan class is Improved Touring for V8s. To build this car, Mitchell started with a stock Mustang GT. The rules allowed him to bring the weight down to 2930 pounds, about 350 less than the street car. Once again the interior was stripped out and replaced with a single racing bucket, and again an elaborate rollcage was woven through the cockpit. SVD also fit a 24-gallon fuel cell in place of the original 20-gallon tank.
American Sedan rules restrict the Mustang GT to a single Holley 600-cfm 4-barrel carburetor, under which sits Ford's classic 4.9-liter pushrod V8 with cast-iron GT40 heads. With the usual race prep, Mitchell extracts 386 bhp and 364 lbs.-ft. of torque from this engine, compared to the road car's 215 and 285, respectively. (Yes, Ford has killed the pushrod Mustang in production, but the racing world still embraces it.) Once again, a lighter car with a lot more horsepower and torque results in vastly improved performance.
The AS rules dictate the stock Borg-Warner T5 gearbox, which Mitchell backs up with a 3.73 differential. The rear suspension is similar to that on the World Challenge car, but the front suspension remains stock. The rulebook limits the mods here to simple adjustments, through which Mitchell tries to tame the racer's 16-inch Panasport wheels and 255/50VR16 Goodyear GSCS tires.
The brake rotors are also stock Mustang parts, clamped by Corvette calipers and racing pads adapted with a kit by Baer Racing. This setup is surprisingly effective for a stock-based brake system, but not quite in the same class as the brakes on the World Challenge car.
On the spec page, at least, Mitchell's AS car seems a lot like his World Challenge mount, just with lower power, more weight, and a less narrow-focus suspension. You'd think it would feel pretty much the same, just a little bit slower. Wrong. While the World Challenge car seems rock-solid at speed, the AS comes across like it's dancing on its tiptoes. The stock power steering is much too light and imprecise for a car with this much performance, and the rear axle is subject to violent and uncontrolled tramp under hard braking.
At $50,000, the AS also represents nearly as costly a prep job as that of the World Challenge car. Eric's aging Camaro is now worth maybe 18 grand, so the AS Mustang would be a $30,000+ investment to give away a second a lap! No sale there.
I'm fascinated by the economics of amateur versus professional racing. You could buy a quality used American Sedan racer like Eric's Camaro for less than $20,000 and, if you avoided wrecking it, spend about $10,000 per season for engine rebuilds and mechanical maintenance. In addition, Eric budgets a paltry $1500 per race for tires, entry fees, and travel.
By comparison, a dozen-race World Challenge season can cost $30,000 per weekend when you include devaluation of the car. Realistically, neither class is going to bring you to the attention of Frank Williams or Roger Penske, but the price difference between lapping Lime Rock at a minute flat versus 58 seconds seems inordinately steep-even if the World Challenge car is infinitely more fun to drive.
Mustang Road Car
Our long-term Mustang Cobra offers the best street-legal performance you can get for under 30 grand, with the possible exception of the $20,000 Camaro Z28 1LE. That brings up the question we came to Lime Rock to solve: What's the difference between a hot street car like this one and a purpose-built racer of the same type? At Lime Rock, the answer is "about eight seconds"-not much time to normal folks, but an eternity amongst racers.
For example, the outright track record here-set in an IMSA GTP car-is about 44 seconds. Full-blown Trans-Am racers lap in the 52- to 54-second range, and Showroom Stock Corvettes will circulate at 1:03 or so. Eric and I were lapping at 1:08 to 1:10 in our Mustang Cobra road car, about as fast as you'll go in anything that hasn't been race-prepped. More mundane street machines usually turn a 1:15 or 1:20.
Race Versus Road
So why is a road car so much slower than a racer? Tires are a big part of it: The 245/45ZR17 Goodrich Comp T/As on our street Cobra are as aggressive as any road tire sold today, but they're mild as a milkshake compared to the racing Goodyears on Mitchell's cars. The tradeoff for the super stiction and grip of the competition rubber is wickedly fast treadwear, lots of noise, tooth-rattling sidewall stiffness, and a huge buy-in cost.
Suspension geometry is another big difference. You can see large gray scuff marks halfway up the sidewalls of the street car's Comp TAs-even the rears-because the suspension isn't set up to keep the tread flat on the pavement at 10/10ths cornering. Instead, more practical considerations such as ride comfort, production cost, safe handling in the hands of the uninitiated, and tire life take precedence.
Brakes are a third consideration. Racing linings don't have to last 30,000 miles, go through thousands of heat cycles, or resist eating up the rotors. Competition brakes only have to last long enough to win one race, and if the whole system is junk after that, well, such is the price of victory.
Power is another major factor. At 305 bhp and 300 lbs.-ft. of torque, our long-term street Cobra's DOHC V8 is one of the highest-output engines on the market. Even so, it's a hopeless wimp compared to a 420-horse World Challenge 351. Most people assume Federal regs are to blame, but street mills actually lose very little to emissions controls. Affordable production is the real issue-all the labor-intensive prep work and high-priced, high-strength parts that make a racing engine so strong would drive a road car's sticker to the moon.
Weight makes a huge difference, too. That 500 pounds that Mitchell eliminated from his World Challenge Mustang is 500 pounds that don't have to be slowed for a corner, wrestled through the apex, or accelerated back up to speed. That means that all the other components in the package can be correspondingly lighter-or, in the case of class-mandated equipment, less heavily stressed.
Finally, overall feel is the last big factor. The key performance secret behind Bill Mitchell's World Challenge car is how comfortable it feels at speed-at 10/10ths it is predictable, smooth, and confident, all of which lets the driver reach top speed quickly and maintain it over time. A stock passenger car-which is rarely driven at more than 4/10ths but has to deal with potholes, parking curbs, tar strips, and so on each and every day-will always feel tentative and dicey by comparison.
Even so, in terms of engineering, a race car that can circulate Lime Rock at one minute flat is pretty damn impressive, but a street car that can turn consistent 1:09s with the air-conditioner on, a CD playing, and a passenger riding shotgun is a heck of a lot harder to create.
Shopper's Corner
Eric Morrow and I didn't come to any startling conclusions after our test session. Sure, if we were moderately wealthy guys we'd commission SVD to build each of us one of the Challenge cars, but oh well....
In lieu of having 300 large rattling around in our pockets, we did at least prove a few things to our satisfaction. One, that yours truly is still a pretty decent jockey, at least when Bill Mitchell's the guy saddling the horses. Two, that Eric Morrow has a good deal going with his current AS Camaro, so there's really no need to change. And three, that it's a heck of a lot of fun to drive real fast in somebody else's race cars!
And I guess we also proved that tired old racing axiom once more: How fast you want to go depends on how much you want to spend!
Essentially, the American Sedan class is Improved Touring for V8s. To build this car, Mitchell started with a stock Mustang GT. The rules allowed him to bring the weight down to 2930 pounds, about 350 less than the street car. Once again the interior was stripped out and replaced with a single racing bucket, and again an elaborate rollcage was woven through the cockpit. SVD also fit a 24-gallon fuel cell in place of the original 20-gallon tank. 