K.J. Jones
February 5, 2008
Kevin Booth scored this bad-dude, '07 Shelby GT 500 in an eBay deal withan Illinois Mercedes dealership and saved a ton of cash. Our testvehicle came to us having nothing more than a few suspension modsalready done and low miles on the odometer. That's the way we like 'emfor these kinds of projects--mechanically bone stock.

Horse Sense: Prices are an interesting issue withShelby parts. On one hand, once you look at MSRPs, you realize there arebetter deals on the Internet and through wholesale performance outlets,such as Summit Racing (www.summitracing.com). On the other hand, pricesare irrelevant for those who can afford a GT 500.

Sometimes even we, the staff of 5.0 Mustang & Super Fords, are amazed bythe effect hype has on 'Stang enthusiasts. In a nutshell, it sometimesmakes 'Stangbangers go absolutely nutty. Sure, we do a fair amount ofboasting about cars or parts that truly impress us. When we're reportingon solid-gold winners, and even the one-hit wonders, our main objectiveis to keep the information real and present to you the facts--especiallywhen we experience them firsthand.

Word of Gibson's new X-shape crossover sparked the initial flame forthis tech project. The 21/2-inch, mandrel-bent aluminized steel (alsoavailable in stainless) tubing dramatically increases exhaust flow overthe restrictive factory piece and its catalytic converters.

Hype certainly played a big role in the immediate success of Ford's '07Mustang Shelby GT 500. From the moment 'Stang nuts first heard rumorsthat Ford might build and offer a supercharged S197 to the car'sofficial announcement, production, and eventual rollout in fall 2006,energy for Shelby coupes and convertibles has remained high. While thenear $100,000 markup prices for new Shelbys have come down considerably,the cost of a new GT 500 still ranges between $50,000-$60,000.

The Shelby's Eaton-blown 5.4 engine and its advertised 500 hp sits highon the car's hype ladder. For the enthusiasts lucky enough to own onebut don't really understand the difference between flywheel andrear-wheel performance, boasting about its 500 ponies comes naturally.The pride owners have in their investment is certainly understandable.

Our second phase of product test centers on K&N's new AirCharger CAIsystem for '07 GT 500s. The air-intake kit eliminates the restrictiveflow of the OEM airbox/filter combination. As we saw in our tests, itrams a huge amount of air into a Shelby's supercharged 5.4.

We hard-core 'Stangbangers know that when it comes to claiminghorsepower that's worth bragging about, all bets cancel at the rearwheels--not the flywheel. At this point, it's widely known that the"500" in a Shelby GT's name represents 500 hp. Since the number is oftenmisunderstood as being rear-wheel horses, we thought we'd try to clearthings up by installing and dyno-testing a few Shelby-specific bolt-onsthat should make Ford's super 'Stang live up to its name, and moreimportantly, its lofty power claim.

The parts assortment, installed by Saul "The Surgeon" Gutierrez ofExtreme Automotive in Canoga Park, California, consists of Gibson's newcatless, 21/2-inch X-shape crossover (PN 619008; $226.65/aluminized,$346.65/stainless steel) and exhaust system (PN 619006; $652.35), K&N'sShelby GT 500 AirCharger cold-air intake kit (PN 63-2571; $449.00), anda 2.6-inch supercharger pulley with 90mm tensioner pulley/160-degreethermostat/custom-SCT-tune package (a.k.a. Pulley Pack PN 900045;$599.00) from Paul's High Performance of Jackson, Michigan.

Paul Svnicki of Paul's High Performance offers this 2.6-inch blowerpulley and 90mm tensioner-wheel setup designed specifically for ShelbyGT 500s...

If this parts list seems familiar, it's probably because these are thesame entry-level upgrade parts you've read about in our similar testsfor Fox, SN-95, New Edge, and Three-Valve S197 'Stangs.

Kevin Booth was kind enough to lend us his Shelby 'Stang for a day ofinstallation and dyno evaluation at Extreme. All tests were done withengine temp constant at 170 degrees, but we noticed that the GT 500'siron-blocked engine doesn't dissipate heat well. Since heat rises, theblower remains heat soaked for quite a while after the engine has beenrun hard.

...Paul's upgrade system includes a 160-degree thermostat and acustom, SCT flash tune that optimizes air/fuel accordingly, with regardto increased intake and exhaust airflow, for smooth, low-rpmdriveability.

As usual, our testing is done with California's 91-octane pump gas,which with proper tuning, we feel can be used up to a 550hp limit onShelbys. Naturally, race fuel permits making more power, but keep inmind the connecting rods in Shelby engines aren't forged and are likelythe first parts to go when they're taken to the limit.

As you'll see when you read further, there are individual and collectivemerits for all these simple Shelby bolt-ons, making them smart choicesas first-step upgrades for enthusiasts who like to boast.

Here's a comparative look at Gibson's new X-shape crossover (left) andour test Shelby's OEM catalytic crossover tubing. Other than the obviousabsence of cats, the other major differences between the two are the Xintersections on each. While the stock cat pipe's X gives the impressionof gasses meeting in a smash-mouth fashion, Gibson's pipe features aradiused merge, which disperses exhaust smoothly and with much greatervelocity than a stock pipe. Shelby fans need to understand that thiscrossover isn't legal for street use, as it doesn't include catalyticconverters.

Gibson Exhaust

Swapping crossovers and bolting on Gibson Performance's after-catexhaust system is the first leg of our Shelby upgrade journey.

Unlike exhaust on its Fox, SN-95, and New Edge predecessors, there's nocutting necessary when removing exhaust systems on S197 Mustangs, sotaking the tubes off our test car is a quick and easy deal. Installingthe Gibson X-shape crossover is a drama-free experience, and each pieceof the kit's exhaust piping fits without any modifications.

The sound created by a blown 5.4 with no cats is different, and quitefrankly, it takes getting used to. Decibel levels jumpdramatically--both at idle and especially when the hammer is dropped--asthe engine takes on a much louder, deeper, and raspier note. The soundis completely different than the stock exhaust, which seemswhisper-quiet in comparison.

Without tuning, the exhaust swap showed us a nice power bump and anearly identical gain on the torque side. Going catless with a Shelby'sexhaust is a good first move, as it will ultimately benefit from all theengine-performance upgrades an owner will make as time goes on.

The K&N AirCharger is bench assembled first. Saul transfers the GT 500'sOEM mass air sensor using hardware supplied in the kit. Fittings andgrommets for the factory crankcase vent hose and vacuum vent line arealso installed at this time. A rubber weatherstrip is placed around theheat shield to ensure good contact with the 'Stang's hood when it'sclosed. It also creates a pocket that prevents underhood hot air fromleaking into the cold-air-inlet area.

K&N AirCharger

We've been itching to give K&N's Shelby GT 500 cold-air system a try fora long time. We learned about the AirCharger and itspower-increasing-potential for GT 500s in January 2007 after meetingwith representatives from the company to discuss products and projectopportunities.

For the Shelby 'Stangs, K&N eliminates the super-restrictive, factoryair inlet and airbox assembly and employs a large, conical, high-flowair filter and straight-shot inlet tube. The tube fits cleanly into theengine compartment using the included factory silicone couplers and asingle anchoring bracket.

The AirCharger definitely adds insane rear-wheel power, even with thenew exhaust's gains taken out of the equation. We inspected the sparkplugs after our final dyno run and discovered that the horses come at apotentially huge expense. Ashen-white spark plugs tell us the systemwill be better served by a custom tune. With that, we move on to thefinal stage of our testing.

After loosening the serpentine belt, this Paul's High Performance 90mmidler wheel is bolted to the stock belt-tensioner arm with the noncoatedside facing the engine block. Paul's provides a new bolt with eachtensioner pulley, as the factory pulley's bolt can't be used. The newtensioner is required for the 2.6-inch blower pulley to ensure belttightness isn't compromised by taking up the small amount of slackcaused by the smaller piece on the blower.

PHP Pulley and Tune

While its 5.4 bullet speaks volumes about the uniqueness of a Shelby GT500, the Eaton Roots-style supercharger that sits atop the engine isdefinitely its piece de resistance.

In stock trim, we've seen as many as 8 psi of boost pump through a GT500's powerplant and make its bone-stock horsepower a respectable 440 to448 at the tires. That's not quite the hard 500 horses that themisinformed believe are hitting the ground.

Our test Shelby fell within the proven stock parameters, but as ourfinal tests confirm, there's always room for improvement.

To close out our research, we called Paul Svinicki of Paul's HighPerformance and ordered his company's 2.6-inch blower pulley and 90mmtensioner package, as increasing boost by speeding up the superchargeris the best plan of action with stock Shelbys.

Removing the stock pulley on a Shelby GT 500's Eaton supercharger takessome doing. The pulley is pressed on with the attitude that it won'tever be removed, so be prepared to crank on the pulley extracting toolfor a while before it finally breaks free with a loud pop.

At this juncture, remapping the PCM is a must, due to the radicalchanges the smaller pulley makes on the engine's air/fuel mixture andthe other modifications we've made.

Custom-tuning on the dyno is the best way to get the most out of anyperformance enhancement for EFI 'Stangs. Paul is top-notch when it comesto using SCT's tuning software to dial in a modular engine.

Because we know you're asking, no, Paul didn't come to California toassist us. The tune for our test ride was set up at PHP in Michigan on asimilarly configured Shelby. It was loaded into SCT's XCalibrator 2handheld flash tuner. Once the plugs were installed and gapped down to0.028-inch and PHP's 160-degree thermostat was in place, Saul loaded thePHP calibration into the Shelby's PCM. It was time to hit the dyno for afinal look at the overall effect these simple performance upgrades haveon Kevin's once-stock Shelby.

To give you an idea of how things worked with the cross-country tuning,Paul's tune was almost spot-on for air/fuel (his test Shelby still hadcats in place), and the rev window for the blown 'Stang increased andnetted 10 psi of boost, thanks to the PCM update. All we added wasapproximately 4 percent more fuel to the tune and finished up withreally impressive overall results.

The simple group of bolt-on parts now has Kevin's Shelby living up tothe 500hp value that's part of its already famous name.

Times Table

With the exception of dyno testing--unless you have a chassis dyno inyour garage--all the parts can be installed in do-it-yourself fashion,provided you have basic sockets, ratchets, and wrenches; air tools arehelpful but not required. The supercharger pulley requires a specialtool to extract it, and we recommend you check with Paul's HighPerformance to find out more about acquiring one.

Here's an at-a-glance look at the approximate amount of time you'llspend installing the bolt-ons yourself:

Gibson exhaust: 45 minutes

K&N AirCharger: 20 minutes

PHP 2.6-inch pulley and 90mm tensioner wheel: 40 minutes

PHP 160-degree thermostat: 10 min