Steve Turner
Former Editor, 5.0 Mustang & Super Fords
November 7, 2013
Photos By: Courtesy Of VMP Tuning

Horse Sense: If you're wondering how Justin Starkey pumped up his '12 Boss past 800 rwhp, the short answer is with one of his supercharger kits. The long answer appears on page 112 of our June 2013 issue ("Boost 302").

We live in a wonderous time, when streetable horsepower is readily available in bolt-on packages. Thanks to the advances in modern tuning, these parts can deliver huge power and still retain the kind of driveability that keeps them enjoyable to drive. It really is cool.

Of course, this is even more true with the likes of Bosses and GT500s—the factory power is impressive and the modded power is insane. In the case of Justin Starkey of VMP Tuning, he's able to bolt on the parts and tune the cars. He has a stable of insanely powerful cars, one of which is a Boss 302 featuring one of his VMP superchargers. We covered it here, and it made 842 horsepower—at the wheels!

That's a huge number, and the torque wasn't far behind at 732.49 lb-ft. With that much power and grunt on tap, it's not a huge surprise that the stock clutch might not be up to the task. In the case of Justin's Boss, it wasn't an out-and-out clutch failure, but some odd behavior on the Dynojet that suggested it was on its way out the door. "The stock clutch was staying on the floor, and I was afraid it was beginning to slip on the dyno," Justin said.

Knowing that he likes to put his Boss through its paces on the road course, Justin needed to select a clutch that could corral that kind of power but still retain a driveable level of pedal effort. With that goal in mind, Justin selected McLeod Racing's RXT twin-disc clutch, which is designed to lasso up to 1,000 horsepower with light pedal effort.

"I went with the Mcleod RXT because they have a great reputation," Justin explained. "The dual-disc design drove well, but still had the holding power I needed with the blower."

Of course, like any project, there's a list of other while-you-are-at-it upgrades that you could do alongside the must-do mod. In this case, Justin decided to upgrade the clutch-fluid line with Ford Racing's high-performance replacement, and the shifter with MGW's short-throw beauty.

Check out the captions as we hit the highlights of Justin's drivetrain fortifications. He was back to the track shortly after completing these, so you know he was confident they were up to the task.

"The car performed very well at the track with the MGW shifter and Mcleod clutch," Justin added. "It shifted gears well, and I was able to make 2-3 and 4-5 shifts much more easily."

This might be the hardest part of any trans, clutch, or shifter work. Yes, Ford puts healthy dose of aggressive thread-locking compound on the shifter handle. Therefore the stock knob just doesn’t want to budge. If you don’t mind ruining the knob, you can use a large pair of locking pliers. Justin opted to preserve the knob by using a strap wrench and a bit of warming assistance. After heating the knob up to 180 degrees, the knob came off unscathed with the strap wrench.
With the shift knob out of the way, Justin moved on to removing the transmission. He first unbolted the crossmember; then removed the driveshaft, which freed up the rear of the trans.
After removing the crossmember, Justin moved the transmission jack into place. When you are doing these jobs, the proper tools are critical, and that’s definitely the case here, as once the trans is unbolted from the RoadRunner engine, you’ll certainly need help getting down slowly and carefully.
Justin and VMP’s Steven Cleveland placed the factory Getrag MT-82 six-speed manual transmission on the shop floor, and it was finally time to remove the wounded stock clutch. “The stock clutch was acting funny on the dyno with the VMP-TVS on high boost,” Justin explained. It wasn’t fully slipping, but chattering a bit, so he knew it was near the end of its lifespan.
It’s usually an option—especially on a low-mileage car—to resurface the stock flywheel and reuse it with your new clutch. You can do so with the McLeod RXT clutch that Justin selected, but the company recommends an aftermarket flywheel like its own offerings.
Just by comparing them with the stock parts, you can tell the McLeod pieces are more serious. Sure they are handsome, but it’s not just the red paint that differentiates the McLeod RXT Street Twin (PN 6932-2; $1,125). Its pressure plate works with two ceramic friction discs, a floater plate, and a McLeod adapter ring to corral up to 1,000 horsepower with what the company describes as “light pedal effort and excellent street characteristics.” That’s just what the doctor ordered for an 800-plus-rwhp Boss.
After tapping in the necessary dowels, Steven installed McLeod’s aluminum flywheel (PN 563408; $474) designed specifically for the company’s RST and RXT clutches. CNC-machined from a chunk of billet 6061-T6 aluminum, it features a serviceable steel friction plate and a hardened-steel ring gear. Despite its rugged good looks, it only weighs 13 pounds, which is about 10 pounds lighter than the stocker. Fresh ARP bolts are supplied with the flywheel and they are torqued to 75 lb-ft in a star pattern.
Using the supplied alignment tool, Steven slides the new RXT clutch (PN 6932-25; $1,125) into place using the dowels in the flywheel to line it up. He then bolts the adapter plate to the flywheel using the factory hardware, and torques the fasteners to 25 lb-ft in a star pattern until the fingers start pulling toward the flywheel, then to a final spec of 35 lb-ft. The RXT clutch is pre-assembled, so the adjustment incumbent with some twin-disc arrangements isn’t necessary. Be sure to break in the new clutch according to the instructions (not on a chassis dyno) before you start to really enjoy its grip.
As a precaution, Justin opted to replace the throwout bearing and hydraulic slave with new Ford parts in case it was damaged. This reduces the chance that the VMP crew will have to remove and replace the transmission again.
While the transmission is out, it’s a perfect time to upgrade the flimsy factory MT-82 shifter. Justin opted to upgrade his Boss with MGW’s short-throw shifter ($390). Comparing the two, it’s obvious the MGW (foreground) is more robust. It also offers internal centering springs to help with the 2-3 shift and a 30-percent reduction in throw.
Likewise, replacing the hydraulic slave meant breaking into that system. Since the master cylinder would need filling and bleeding, it was an opportune time to replace the plastic factory clutch-fluid line with Ford Racing Performance Parts High Performance Clutch Fluid Line (PN M-7512-A; $259.95). We have felt what a large difference this line makes in clutch feel, as the stock line can expand with the fluid gets hot, which degrades the clutch actuation.