Twin Turbo Mustang GT 500 - Compound Rapture - GT500 Twin-Turbo

Travis uses SCT's Advantage... 

   

  read full caption

Travis uses SCT's Advantage III tuning software and XCalibrator 3 flash device to create and load a power-churning tune into the PCM of his newly compound-boosted Shelby GT500. The addition of turbos does not affect the engine's ability to start and run, but there's no way the hammer can be dropped the way it should be until you've got a good, pump-gas tune and safe air/fuel ratio (11.7:1) at wide-open throttle, which can only be achieved by having an experienced tuner like Travis Franklin dial it in. As an authorized Hellion Power Systems dealer with an in-house test Shelby, Gear Heads is working on developing custom SCT dyno tunes that are specifically calibrated for the new GT500 twin-turbo systems it sells.

On The Dyno
OK, up-front, we're now officially honest-to-goodness fans of the blower/turbo matrix, and we really dig Hellion Power Systems' twin-turbo setup for factory-supercharged, Shelby GT500 Mustangs.

The system makes big steam, and stupid torque in a hurry, as you see in the comparison of our project's baseline and two samples of the final dyno numbers! Lengthy spooling time and high impeller speed for the turbos is virtually nonexistent, and the power adder achieves its preprogrammed (16 psi for our test) boost limit almost as soon as you roll into the throttle. "I wanted the turbo system to give Shelbys the low-rpm power they lack and sustain that power through--and especially at the top of--the rpm range," says Hellion's owner John Urist.

Travis' Hellion-dressed Shelby... 

   

  read full caption

Travis' Hellion-dressed Shelby GT500 had the rollers rockin' on Gear Heads' Dynojet during the post-install dyno test, putting down effortless at-the-feet horsepower and torque that steadily increased with each tuning change (timing/fuel increases). The turbochargers spool almost instantly and are deceptively quiet, which is something we weren't expecting. It really adds to the overall cool of the whole boosted-boost concept.

Our goal going into the experiment was to achieve at least 700 rwhp with compound boost on 92-octane pump gas, without exotic or aftermarket super-duty parts in the engine. The bullet under the hood of the '08 Shelby at Gear Heads was as stock as they come, with no issues other than surprisingly lower baseline power going into our test (compared to other Shelby projects). It emerged completely intact and still running like a stocker (at idle, cruising speeds, and so on) after an intense session of dyno flogging and relatively little tuning.

Note that our after-baseline dyno figures are categorized as Turbo 1 and Turbo 2, and represent numbers produced with the twins and the blower doing their thing. The readings in Turbo 1 were achieved with 16 degrees of timing and an air/fuel mixture that is relatively fat throughout the dyno pull. With a degree more timing and slight trimming of fuel, Travis had our test 'Stang pumping out 700 hp at the rear tires with no sweat.

While the performance capability of this system for stocker Shelbys is crazy, the maximum amount of power we recommend for this system--on an engine with factory internals--is about 725 at the tires. Of course, engines with extensive mods can generate much more (even with pump fuel). We have no doubt that the magic thousand ponies will run absolutely wild with Hellion's optional 66mm hairdryers in place.

Obviously, we tested the setup as a compound-boost-style power adder with the OEM blower in place and functional. However, John has designed the system so it can be installed on a Shelby's 5.4-liter engine in a non-compound manner as well. This requires removal of the blower's internals or a custom-fabricated intake manifold to make it possible.