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.
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.
Photo GalleryView Photo Gallery
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.