Muscle Mustangs & Fast Fords
Project Smog-Legal Killer - Power to the Pavement
Turning our smog-legal horsepower into forward motion.
It's been said that power is nothing without control. Well, whoever muttered those words must have been a proper gearhead because there's nothing more frustrating than losing a race because of insufficient traction or bum drivetrain components. Unless you're an Internet hero, excuses like "I don't have traction" or "I can't powershift" don't cut it.
If you're just tuning in, last month we tied up some loose ends on our Smog-Legal Killer with an MSD shift light, AEM Failsafe wideband gauges, and Flex-a-lite electric fans. The mods were aimed at improving our shift points, protecting the motor from a lean condition, and freeing up power.
Speaking of power, after ditching the stock mechanical fan, our coupe gained 11 hp and 22 lb-ft of torque at the wheels on the dyno at Advanced Engine Development (AED) in Shingle Springs, California, for new totals of 523 hp and 530 lb-ft of emissions-friendly horsepower.
Before the chip tune, we visited Sacramento Raceway (when it was making 422 hp and 419 lb-ft) and made a best pass of 11.99 at 121 mph. Say what? Yeah, you read that right—just an 11.99.
The trap speed was proof of the available power, but with a stock T5 transmission, axles, and control arms, and a worn Traction-Lok differential, our 60-foot times were hovering in the 2.0 to 2.2 range. The weathered components were hurting our e.t.'s. Forget high-rpm launches or powershifting. Instead, our best launches were achieved with mild clutch slip, followed by WOT after the chassis settled down in Second gear—anything more and we'd see one-tire fire.
With the sticky Mickey Thompson ET Radials aired down, we again came up empty-handed as a hard launch snapped a stock axle. OK, so hard launches were out. How about power-shifting? We think not, since the stock T5 was getting louder by the run and any hard shifting resulted in grinding and crunching. In other words, we had plenty of power and no way to put it down. To say it was frustrating would be an understatement. We had to do something.
Its drivetrain and suspension flaws were glaring, but instead of getting overwhelmed at the massive undertakin,g we decided to tackle the project one step at a time, starting with a call to the Mustang gurus at Latemodel Restoration Supply (LRS).
It only took a short conversation with Jonathan McDonald of LRS, one of the in-house Fox-body specialists, to devise a plan. First on our list was addressing our traction issues with some key mods. Our initial reaction was to dive straight for the race-ready parts, but McDonald reminded us that a proper street car needs to perform well at the track and still remain civil when in public. With that in mind, we dismissed the thoughts of a spool and suspension components with Delrin bushings. Instead LRS had a different plan of attack: affordable mods for the street and strip.
"Before ordering parts, it's a good idea to decide what direction you'd like to take your ca, and ultimately where you'd like it to end up, that way you can buy the appropriate parts to reach your goals," McDonald said. "A spool and suspension components with Delrin bushings are awesome at the track, but can be too extreme for some people on the street—it pays off to have a solid plan of attack," he added.
With the notion of a well-rounded street car that also ripped at the track, we decided a rearend overhaul was in order. With the help of LRS, we selected a slew of Ford Racing Performance Parts (FRPP) and LRS components. An FRPP Traction-Lok with '03/'04 Cobra and GT500 carbon-fiber clutch packs (PN M4204F318C), an LRS rear-gear installation kit with FRPP 3.73 gears (PN LRS-4209FRB-K), 31-spline Moser axles (PN MOS-A883151SN), and SVE upper and lower control arms (PN SVE-5649AT) rounded out our roster of power planting mods.
The Traction-Lok is undoubtedly one of the most versatile differentials for performance, price, and longevity. Sure, a True Trac might be better for corner-carving and a spool can be more advantageous in a straight line, but neither can handle cornering and launching as well as a Traction-Lok.
As many of you already know, the Traction-Lok is a clutch-pack-style limited-slip differential that uses clutch discs and plates to apply traction to both wheels. This not only makes for a versatile differential, but it also means the unit is easily serviced when the old discs are worn out. Which brings us to our decision to use a new FRPP unit from LRS.
Even after nearly 300,000 miles of service and numerous rebuilds on our old Traction-Lok, if our motor made less power we could have likely rebuilt it and called it a day. But with so many miles under its belt, we thought it wise to start with a completely new unit since 500 hp can quickly wreak havoc on worn drivetrain components. We consider it cheap insurance, not to mention the new one also comes with the upgraded Kevlar clutches. Ours came spec'd for 31-spline axles, another wise upgrade for serious power planting.
As anyone who's installed rear end components can tell you, it's not the big parts that kill you, but rather all the seals, oil, shims, and small bits. But thankfully LRS has taken the guesswork out of the equation with its rearend installation kit, which comes with everything needed to get rolling, save for wheel bearings and axle seals.
Like our worn Traction-Lok, the coupe already had FRPP 3.73 gears, but with more than 150,000 hard miles on the gears, we thought a new set was definitely in order. The LRS kit came with the FRPP ring and pinion gears, a master bearing and shim kit, FRPP friction modifier, Royal Purple 75W-90 gear oil, all gaskets, seals, and even marking compound. Seriously, the kit came with everything needed for a carefree install. Forget rushing to the local auto-parts store for a gasket or seal—the LRS kit saves the hassles.
With a new differential and gears in place, it was time to select quality axles. We upgraded to Moser 31-spline, Fox-body-length, five-lug axles from LRS. These burly units up the spline count from the stock 28 to 31 for more strength. Speaking of strength, the Mosers are made from hardened steel for the utmost durability.
Before wrapping up the rearend revamp, we ditched the stock upper and lower control arms for SVE tubular units made from heavy-wall tubular steel. These are far stronger than the flimsy, stamped-steel Ford units that are notorious for inducing wheelhop.
The SVE units aren't just made from stronger material—they're leagues ahead of the stock units, thanks to Energy polyurethane bushings and grease fittings that make greasing the units a breeze. They're also beyond affordable.
A quick note about the grease supplied with the control arms—be sure to use this special polyurethane bushing grease most commonly found in the small packets from Energy or Prothane. Also, don't forget to liberally spread it throughout the entire surface of the bushings for the best performance.
When it came time to install the rearend components, we paid a visit to Stephens Speed Shop in Martinez, California, where long-time racers Ken Stephens and Jeremy Stanton handled the wrenching. While installing rear end components isn't rocket science, correctly setting the gear backlash can be tricky and is better left to someone with experience. We've seen too many gearsets burn up in short order from improper backlash.
In a matter of hours, Stephens Speed Shop had the withered, old components out and the new stuff installed. Another benefit to ordering parts from LRS is their unparalleled customer service and tech support. We had several questions during the install and their techs were only a phone call away. Follow along with the photos as we take you through the rearend revival process.
Here's to the first step of putting our smog-legal power to the pavement. We're keeping the next installment under wraps for now, but Hang tight. We've given you a hint of what's to come.