If you're the owner of a GT500, you already have an addiction to power-otherwise you wouldn't have bought one in the first place. So it should be no surprise that many GT500 owners are relentless with modifications to their beloved Shelby (that they originally intended to keep stock). Each modification adds just enough power and torque to suffice-for a while. Then, it's back to the local shop or the Web for the next upgrade.
Some of the first mods are usually the typical bolt-on components-cold-air intake, throttle body, pulley, headers, and tune. Though that's more than enough to satisfy most. Enter Justin Starkey and his '07 GT500. Starkey owns and operates VMP Tuning, and bought his Shelby in May 2007.
Starkey's GT500 now features the said bolt-on mods and an FRPP 2.3L TVS supercharger pumping out 18 psi of boost. The only typical bolt-on it didn't have was an after-cat system, which we'll discuss later. On VP C-16 race gas, it made 732 rwhp and 708 lb-ft of torque. Though not bad for a bone-stock short-block, Starkey knew there was more power available. "I've maxed out the blower and can't just put a smaller pulley on it," Starkey said. "I have to find creative ways to make more power."
Justin Starkey of VMP Tuning...
Justin Starkey of VMP Tuning monitors the vitals on his laptop as he makes a pull on the VMP Tuning Dynojet chassis dyno.
The camshafts that Comp recommended...
The camshafts that Comp recommended for our test subject were the intermediate XE-R series (PN 106360), which retail for $1,266.50. Offered in three variations, the XE-R series for supercharged/nitrous applications all feature 0.475-inch lift on the intake cam and 0.450-inch lift on the exhaust cam. The set we chose have a duration of 230/232 degrees.
Our test subject is an '07...
Our test subject is an '07 GT500 with a stock long-block, a TKL FRPP/Whipple TVS, a VMP Tuning elbow, a GT cold-air kit, long-tube headers, an X-midpipe, and a tune.
Teaming up with Starkey, we turned to Comp Cams. It has just released a set of camshafts for the 5.4L Four-Valve, ground specifically for supercharged applications, like the GT500. An extension of its XE-R series, the new camshafts are available in three configurations-depending on application-and sell for $1,266.50 a set. All three feature 0.475-/0.450-inch lift, and require a valve-spring upgrade.
Designed for street performance with excellent torque output, XE258BH-116 (PN 106260) features 222/224 degrees of duration at 0.050-inch lift. This set has a designed operating range of 1,200 to 5,800 rpm and doesn't require other modifications. If you want a mild power increase coupled with a mild lope, then this is the set for you.
On the other end of the spectrum, the XE274BH-116 set (PN 106460) utilizes 238/240 degrees of duration at 0.050-inch lift. This set is designed for maximum street and strip performance, requires a lower final drive ratio, and features a rough and raspy idle. The most aggressive of the series, this set has an operating range of 2,000 to 6,000 rpm.
Starkey lowered the GT500's...
Starkey lowered the GT500's massive powerplant and secured it. Though some prefer to do the job with the engine in the car, Starkey said that it's just as easy to drop the engine-because of clearance issues.
Because of the aggressiveness...
Because of the aggressiveness of the camshafts, a valvespring change is required (PN 26125-16; 26123-16).
For our test, we opted for the middle-of-the-road XE266BH-116 (PN 106360). Featuring 230/232 degrees of duration at 0.050-inch lift, this set is probably the best intermediate upgrade. Though not super-aggressive, it has a nice large operating range from 1,500 to 6,000 rpm and produces a moderately aggressive idle, yet maintains plenty of streetability for daily use.
Since the GT500's after-cat system was still stock, we decided to upgrade it as well. MagnaFlow sent us a 3-inch stainless steel system (PN 16674), which retails for $921.27. Follow along with Starkey as he installs and tunes the cams and exhaust.
After removing the cam covers,...
After removing the cam covers, Starkey turns the engine over by hand to top-dead center (TDC).
Starkey then uses a timing...
Starkey then uses a timing chain tool manufactured by Ford for dealers to use in their service departments. It wedges in place to hold the primary chain tight, so the timing cover doesn't have to be removed to change the camshafts.
Starkey then releases the...
Starkey then releases the pressure on the secondary chain tensioner and locks it in place with a paperclip. It can then be unbolted and removed.
He then loosens and removes...
He then loosens and removes the bolts holding the timing gears to the camshafts.
Using a permanent marker,...
Using a permanent marker, Starkey makes timing marks on the primary and secondary timing chains.
He then gently pries the primary...
He then gently pries the primary timing gear off the exhaust camshaft.
After removing the cam retainers,...
After removing the cam retainers, Starkey then removes both camshafts together.
Starkey uses compressed air...
Starkey uses compressed air to pressurize each cylinder to hold the valves in place while replacing the valvesprings. Note how he also uses shop towels to block off any passage to the oil pan. One dropped retainer or spring could make this a much more difficult job.
Using a couple cam retainers,...
Using a couple cam retainers, Starkey bolts in place an old camshaft that has had its lobes removed. This gives him more room to replace the valvesprings.
Using a spring compressor...
Using a spring compressor tool, Starkey compresses the stock springs and removes the spring retainers.
The stock valvesprings are...
The stock valvesprings are color-coded-blue for the intake springs and red for the exhaust.
After installing the new springs...
After installing the new springs and camshafts, Starkey then pre-lubricates the camshafts using engine oil.
After reinstalling the engine,...
After reinstalling the engine, Starkey strapped the GT500 to the dyno and adjusted the tune.
After installing the cams...
After installing the cams and adjusting the tune, Starkey's GT500 produced 770 rwhp and 709 lb-ft of torque. Power and torque are both up above 4,500 rpm, and peak power is up by 38 hp. Though power and torque were both lost down low, the loss is worth the gains up high.
The MagnaFlow after-cat system...
The MagnaFlow after-cat system (PN 16674) was the next step-to see if the stock system was holding us up.
Because Starkey had already...
Because Starkey had already installed a 3-inch midpipe, he unbolted and removed the reducers.
Next, Starkey unbolted the...
Next, Starkey unbolted the after-cats from the lead pipes.
He then installed and aligned...
He then installed and aligned the MagnaFlow lead tubes and axle-back muffler
The MagnaFlow system features...
The MagnaFlow system features a mandrel-bent, stainless steel design.
The Magnapack mufflers offer...
The Magnapack mufflers offer a deep, aggressive tone, and are easy to install.
After some more tuning, Starkey...
After some more tuning, Starkey made another pull on the Dynojet. The exhaust system helped, bringing output to 773 rwhp and 720 lb-ft of torque-an increase of 3 hp and 11 lb-ft over the stock exhaust. The gains are consistent throughout the entire curve, even though the conditions were a little better before. A total gain of 41 rwhp and 12 lb-ft of torque may be just what you need to take your GT500 to the next level.