The heart and soul of the revised induction system is the JDM 116mm MAF sensor (arrow). With the factory sensor pegging, our Shelby was severely handicapped. The pegged meter forwarded a signal to the ECM, at which time the ECM can no longer control the fueling of the expensive supercharged engine.
During Part 1, driver Evan Smith noted it was barely necessary to use Fourth gear to avoid hitting the rev limiter in Third. This last-minute gear change brought down the engine speed, which undoubtedly hurt performance. With that in mind, the 4.30 gears were the items of choice as they would not over-rev the car at the finish line, but enable the Shelby to stay within the power band. In most cases, optimal performance comes when the engine is near, or at, redline just as it crosses the finish line in Fourth gear.
Meter Maids
One of the notable aspects of Part 1 was the problem surrounding the stock mass airflow sensor (also known as the mass air meter) of the Shelby and the accompanying airbox and inlet system. Like a normal Mustang GT, the Shelby has a mass air meter that is integrated in the inlet tube and the factory airbox, in which the air filter is contained. Unfortunately, with the custom tune that D'Amore loaded up in Part 1, the engine had increased in performance and reached the limit of the stock MAF sensor.
The stock 3.31 cogs were also hindering our efforts, especially at the finish line. The stock gears left us with two options: keep the car in Third in the lights and annihilate the rev limiter, or crack Fourth and putt-putt to the finish line. To counteract this problem, we swapped out the factory gears for a 4.30-ratio ring-and-pinion gear set from Ford Racing Performance Parts. This got the engine over 6,000 rpm at the stripe.
"The mass air meter needed to be changed because the stock unit was being pegged," D'Amore says. "The meter will register only 5 volts. Once it gets to that point, it pegs and sends a signal to the ECM. With this signal, the ECM interprets the car running in a lean state, and with the new Mustangs being a drive-by-wire system, the ECM closes the blades to the throttle body, thus cutting power.
To combat this, D'Amore had to create a MAF sensor to replace the stock piece. The JDM MAF sensor measures 116 mm, as opposed to the stock MAF sensor, which measures around 90 mm. In addition to the MAF sensor, D'Amore came up with a fresh-air intake kit. With the kit, he ditched the factory airbox and replaced it with an unshrouded high-flow K&N filter. He also unloaded the stock inlet tube for a smoothed inlet tube that promotes better airflow into the throttle body.
In addition to the gears, we threw in a set of QA1 adjustable rear shocks. We were looking for a way to gain an additional measure of starting-line traction, and the 12-way adjustable shocks would allow us to play around until we found the perfect setting. We set the shocks on the 4 setting and let the car do the rest.
With the new MAF sensor, the tune needed to be reworked to take advantage of the increase in airflow into the engine and to make sure that no harm would come to the powerplant. "With the new mass air meter, I had to change the tune accordingly," D'Amore says. "I changed the mass air transfer functions along with the injector variables. A lot of what I changed in the tune is proprietary information, but overall, a lot of things within the tune had to be changed to not only make power but to keep the car driveable."
Shock it to Me, Baby!
As we detailed in Part 1, launching the car on stock tires was extremely difficult, and with the new M&H Racemaster drag radials, there was a fine line between bog, spin, and perfection on the launch pad. Additionally, Smith reported the GT500 had severe wheelhop when doing the burnout. With the power increases we were seeing and expecting from the Shelby, we realized that getting the car to leave hard and consistent would go a long way to helping us use the Shelby's newly found ponies. This meant a set of adjustable rear shocks was in order.
While we waited for the car to cool down after the first run, JDM's Shaun Lacko shimmied under the rear of the car to change the shock settings. Feeling the 4 setting was too soft, Lacko clicked the adjustment up two positions to the 6 setting.
With the Mustang on the lift at the JDM shop, we had the stock rear shocks taken out and replaced with a pair of QA1 Stocker Star 12-way adjustable shocks. The QA1s feature deflective disc-valving technology and are billed to give you increased valving response, control, and consistency. The shock is composed of a 51/48-inch hard chrome piston that eliminates rod flex, and a forged aluminum body that is lightweight and durable. What mainly separates the QA1 shocks from the factory pieces are the QA1s' adjusta-bility. By looking at such things as vehicle weight, tire choice, transmission type, and other vari-ables, you can choose the shock setting that works best. The QA1s were an easy bolt-on, and while they would not add to the power level of the car, they would certainly help us in applying the power to the track surface.
Tracking the Monster
With everything bolted-on and ready to go, the Shelby made its way to the track for a performance evaluation of the new modifications. Filled with high-test and running on the drag radials, which were set at 16 psi, the same pressure we had them at in Part 1, Smitty swung behind the wheel and strapped on his skid lid. The air was better than it was for Part 1, so we figured the car would pick up a tenth based solely on the weather. In addition, the stiff headwind we experienced in Part 1 had moved around the compass, becoming a slight crosswind, which would have no effect on performance.