Muscle Mustangs & Fast Fords
Project Smog-Legal Killer - Quest for 10s Leads to New Clutch, Anti-Roll Bar
After plenty of problems and several fruitless trips to the track, Smog-Legal Killer finally brings it home.
Every project has milestones and for the Smog-Legal Killer, the 1992 Ford Mustang SSP coupe we've been building up, this update marks a big one. Although the weathered ol' coupe isn't done yet, we finally nabbed the e.t. we'd been chasing since the start.
But we'd be lying if we said it was easy. Like all good stories, it features trials and tribulations, and like most hot rodding tales, many of the problems fell into two categories: user error and plain old dumb luck.
To be honest, our emissions-friendly Fox-body has surprised us on every account. Perhaps we were pessimistic about its power potential, but when we bested our projected horsepower figures, we were both happy and concerned. On paper, we were hoping for 450 hp at the wheels, so when the motor churned out 523 hp, we knew 10s were possible.
For starters, we're at the limits of the stock block, the 42-pound injectors we chose are now too small, and we were 100 lb-ft over the limit of our clutch. Hmm, now what? Well, like any real-world racer, we decided to save the money and try for the 10s.
With our new G-Force T5, Ram Powergrip clutch, and some sticky 28x10.5-15S Mickey Thompson ET Drag tires, it was time to let this sucker fly at Sacramento Raceway. As for suspension, it still had the worn (200,000 miles of worn!) Lakewood shocks and Eibach Drag springs accompanied by some new stuff, like SVE upper and lower control arms, and all new rear end internals from Latemodelrestoration.com.
To say our suspension combo was simple and a bit compromised would've been an understatement. In addition to the mismatch of old and new, the car also lacked any sort of anti-roll or swaybar. We knew the car might be a little hard to control at the strip, but we literally had no idea what was in store.
With your author manning the camera, we threw hot shoe Drew Wallace of AED behind the wheel for a few passes. What ensued was beyond scary. With nothing tying the body to the wheels, the car launched crooked and got so hacked out of shape from the twisting, bending, swaying, and floating, we had no idea how Drew kept it headed down the track. After several failed attempts that almost ended in disaster, we decided it was too dangerous to continue with our test. The best we could muster was an 11.22. Strike one.
Without anything securing the chassis to the suspension the car was unsettled, but thankfully Wolfe Race Craft had the easy fix, a rear antiroll bar (ARB). This ingenious piece ties the chassis to the rear axle to prevent unwanted body roll and it helps to plant the tires evenly on launch.
The main bar is constructed of 1-1/4x.0375-inch-wall chromoly tubing with equally stout laser-cut chromoly mounting arms. The main bar is welded to the rear portion of the frame rails and is connected with spherical rod ends to tabs that are welded on the rearend.
The rear bar prevents unwanted body roll by transferring the twisting loads between the bar, axle, and chassis. For tuning, the rod ends can be preloaded to account for driveline torque. The standard unit has been tested down to the 8.40s, and for those looking to go even faster, a double-mounted unit allows for even greater adjustability.
What does this mean from the driver's seat? It translates into straight and controlled launches, better 60-foot times, and the ability to dial in the right amount of traction.
With the new ARB in place, it was time to try again for 10s. Our hopes were high, but like our last track outing, things didn't go as planned. With the tach hovering at 4,500 rpm, we let the clutch fly and the first few moments felt great as the front tires unloaded and the big Mickey Thompson tires bit hard. But just as the coupe began to drive forward, it nosed over about the time the MSD shift-light ignited. A quick shift to Second produced more rpm than acceleration, and at that moment, the unfortunate realization that we'd overpowered the clutch became a reality.
While the clutch easily held WOT on the street, when launching near 5,000 rpm on a tall 28-inch slick, it proved too much for the clutch. That's not to say the clutch was the problem, quite the contrary since it performed remarkably well for being 100 lb-ft over its torque limit. We simply didn't order a big enough clutch. Strike two.
With the Powergrip single-disc out, we stepped up to the big leagues with a Force 10.5 twin-disc unit from Ram. This bad dog can handle over 1,000 lb-ft of torque and plenty of high-rpm launches—it was built to take some abuse.
For those unfamiliar with twin-disc clutches, it's like a standard single-disc unit but with another clutch disc and a mating surface. The more friction area the better since it not only leads to more clamping force and biting area, but it generally leads to less pedal effort since you don't need such a burly pressure plate because you have twice the mating surfaces.
The Ram unit is as quality as they come, and features a strap-driven design that eliminates the floater-plate rattle usually associated with multi-disc units. If you've ever heard a rattling sound in a car at idle, it's likely from the twin-disc clutch.
Other noteworthy features include a poly-coil hub assembly with urethane encapsulated damper springs that are said to offer four times the shock load of conventional clutch springs. Of course the Ram twin-disc units are paired with its billet aluminum flywheels that are unbelievably true and machined to perfection.
The installation process of the Force 10.5 was nearly that of a single-disc, save for some key differences. The first being the many spacers, washers and associated parts needed to keep proper alignment between the multiple mating surfaces of a twin-disc clutch. It's important to pay close attention during the disassembly process, because failing to reverse the order during the install can result in a faulty clutch. It's also important to realize that multi-disc clutches are thicker than single units so clutch throw will need to be adjusted. Our Fox-body application required a cut-down aftermarket clutch fork pivot ball, but hydraulic systems found on later Mustangs might require the input shaft of the transmission to be modified. It pays to do your homework before diving in.
If you take your time and pay attention during the install, it's not rocket science; we were back on the road in about a day. Clutch pedal feel is stock-like soft and equally silent, but this bad dog bites hard. While the entire clutch assembly weighs roughly 8 pounds more than the single-disc unit we removed (38 pounds compared to 46 pounds), that additional inertia made the launches that much easier, albeit at several hundred rpm lower.
Let It Eat
Finally, it was time to buck up or shut up. So we again paid a visit to the famous Sacramento Raceway Park during a test ‘n' tune and hoped for the best.
With your author again manning the camera and Drew behind the wheel, the ol' coupe nosed into the waterbox and the sticky Mickey Thompson's were brought up to temp. Leaving on the green, the car left straight as an arrow with both front wheels a few inches in the air. When the board flashed, our jaws dropped—but not because we were happy. It flashed 11.008! Are you kidding? A double-zero?
There was no way we were going out like that. And so after a sufficient cool-down, we again went big. This time the ol' coupe came out even harder with a hint of wheelspin followed by equal parts of daylight under the front wheels. A few quick shifts later and we finally did it—a smog-legal 10-second e.t. The board flashed 10.804 at 124 mph and we couldn't have been happier.
It Ain't Over Yet
Few things in life are as rewarding as watching your blood, sweat, and tears finally payoff. Sure there are faster cars, and of course, a smog-legal 10-second e.t. is only a blower and tire swap away in a modern Mustang, but to hit an emissions-legal 10 in an old Fox-body—that's something to be proud of.
But don't go thinking we're done yet. We've still got a few tricks up our sleeves. We intend to install a hot new ECU replacement that's going to revolutionize the Fox-body market. We also have more suspension upgrades aimed at preserving out e.t.'s, while transforming our coupe into a proper-handling street car. After all, it's smog-legal, so we plan on spending plenty of time driving the car on the street.
Until next issue, enjoy the rest of the show.