It's pretty much impossible to argue against the notion that innovation and Mustangs have enjoyed a hand-in-glove relationship for almost 30 years. As 'Stangs continue to evolve--from the EFI Fox-bodies that started the late-model phenomenon in the middle '80s to the S197s of today--aftermarket manufacturers are still developing products that are taking 'Stangs deeper and deeper into the high-performance stratosphere.

Hellion Power Systems of Albuquerque, New Mexico, is one of those companies. Led by multi-time NMRA Super Street Outlaw champion John "Do Work, Son!" Urist, Hellion has been considered a major force in the development of bolt-on turbocharger systems for late-model 'Stangs since entering the aftermarket back in 2000.

As a street-'Stang-enthusiast-turned-racing-champion, John knows all about the importance of "boulevard cred," and thus has focused his business on conceptualizing turbo systems that make big steam in cars that see daily usage more so than building setups for NMRA participants or other full-on race Mustangs.

Travis Franklin of Gear Heads Automotive and Performance checks the fitment of the Turbonetics low-mount, 61mm turbochargers that will make boost magic happen when they start feeding the factory supercharger in his '08 Shelby GT500. Travis picked up his low-mile, still-under-warranty Shelby for a song, and was 100-percent ready to set it up with Hellion Power Systems' Shelby GT500 Twin Turbo setup--a performance mod that is about as radical as they get right now for GT500s. Give that man the "ain't skeerd" badge he deserves!

The "Hell Raiser" system was Hellion's initial foray into the world of compound boost (turbos that work in conjunction with superchargers) for factory-blown Ponies. Designed for '03-'04 Cobras, the tricked-out turbo system is highlighted by a pair of Turbonetics 66mm units that blow boost directly into a Snake's blower, creating a multiplied air force that makes far more horsepower and torque (at low rpm) than a Terminator's supercharger is capable of making on its own.

Not to be funny, but we were blown away by the Hell Raiser setup when we saw it for the first time (the system was a unanimous "favorite-product-at-SEMA" selection by 5.0&SF's editors in 2006). The system is clean, innovative, and as we've learned from seeing cars that are outfitted with Hell Raisers, capable of taking a Snake's stock engine to the 1,000-rwhp level in a blink of an eye.

We'd never think of Terminators as being old news, but for the last two years, Shelby GT500s have been the hot ticket when it comes to factory-blown Ponies. With John constantly thinking of ways to make more power--even for cars that already have more than 400 rwhp--we knew it was only a matter of time before we'd hear that a compound-boost setup for the '07-present super 'Stangs would be created and available for us to check out.

John gave us the call in late 2008 and confidently described his latest creation as an all-inclusive, totally bolt-in, upgradable, no-cut (save for the OEM catalytic converters, which are eliminated from the exhaust system), no-weld, no-fabricate deal. He guaranteed it would easily put 700 horses at the feet of a stock Shelby GT500 'Stang, using only a pair of Turbonetics 61mm turbos and a GT500's OEM supercharger to get it done.

"The Shelby's blower is a positive-displacement device that basically takes air and makes it `smaller' by compressing it. Boost from our turbos actually help the supercharger compress and move air into the engine. The stock Roots blower really isn't as much of a restriction as people seem to think, and our Shelby GT500 Twin Turbo system proves this. Power under the curve is the big advantage of this system. There's no turbo lag, and compound boost literally can make unusable amounts of power for street GT500s with little effort," says John.

Claims of big-time rear-wheel horsepower coming easily through the addition of a single or combination of power adders certainly can be true. However, they're still the type of boasts that will quickly bury the needle on our "oh, really?!" meter, almost every time we hear them. With that said, we needed to personally satisfy our interest in the compound-boost setup for Shelbys, and, of course, let you all know what's up, right away.

Ford sets Eaton's M112 Roots-style supercharger on top of the 5.4-liter engines that power Shelby GT500s. Our test 'Stang is stock as a rock; it will be interesting to see how it performs and stands up to compound boost.	The first step and critical "mod" in installing Hellion's turbo system (after disconnecting the negative battery cable and safely mounting the Shelby on a twin-post hoist, of course) is cutting the exhaust tubes and doing away with the factory catalytic converters. That's right--the cats aren't used with this setup, so enthusiasts who fret over passing state vehicle inspections need not apply.	Naturally, the aforementioned Turbonetics 61mm turbochargers are at the head of the contents list for the Shelby GT500 Twin Turbo system ($5,599). However, as this photo shows, there are several mandrel-bent (to maintain strength), stainless-steel tubes essential for completing the compound-boost setup on a Shelby. In addition to the tubing, Hellion includes every bracket, shield, bolt, washer, nut, tube, hose, clamp, silicone coupler, fitting, pump, and wastegate required for installation. The company also offers a 66mm turbo upgrade ($1,190), dual-solenoid electronic boost controller ($595), and an optional secondary intercooler ($995) for those who really want to take their big-steam production to the next level.
Here is a closer look at the system's primary "boost tubes," which are numbered and installed in a series. The tubes are the primary ducts that route the output of each turbo up to the mass-air meter and throttle body.	The turbo-mount tubes--commonly referred to as up-pipes--bolt directly to the factory exhaust manifolds, which feed the hot side of each turbocharger. Note that clearances between the tubes, chassis, and transmission are tight, so there is a slight bit of finagling involved to get things properly seated and fastened, especially if you have big hands.	Travis installs this adapter log in the 5.4's oil-pressure-sensor location. The log has provisions for the sensor, as well as two AN fittings that will feed oil to each turbo to keep them cool and properly lubricated.
After hanging the turbos (on the up-pipes) and lightly securing them, Travis attaches the exhaust-discharge tubes (downpipes) to each huffer, using high-temp orange silicone to ensure tight, leak-free seals. The bolts around the exhaust and compressor housings on each turbo are left loose, allowing Travis to clock the turbos properly when the boost pipes are installed. When it's all said and done, there will only be -inch of clearance between the compressor housing and the Shelby's transmission. It's close, but it all fits.	Two Turbonetics 38mm wastegates regulate boost for each turbo. The watsegates are outfitted with 9-psi springs at the factory. However, since Travis is also installing an optional electronic boost controller,...	... a set of 5-psi springs are swapped into each wastegate, giving Travis more flexibility to trim the boost output with the electronic device. With the smaller springs in place, we estimate the system's compounded boost pressure should be 15-16 psi at the intake manifold.
A small amount of bench work is required before the turbos can be hung. Oil-drain flanges (one of which is being installed in this photo), gaskets and 3/8-inch NPT fittings are included with the twin-turbo system, so there's no need to make a run for hardware in the middle of the install.	Hellion offers a cool (pun definitely intended) secondary intercooler for the Shelby GT500 Twin Turbo system, which works as a support device for the blown-'Stang's factory intercooler and heat exchanger. Supercharger heat soak is probably one of the only unavoidable nuances for GT500s. According to John, the additional 'cooler is not used in series with the car's other OEM cooling. Instead, coolant for the secondary unit parallels the factory system. With this arrangement, water for both intercoolers maintains the same temperature and helps alleviate what would be a quicker advancing and longer lasting heat-soak condition. Using the supplied bracket and hardware, Travis installs the unit in a pocket behind the front bumper cover on the driver side, and then plumbs its coolant source and output (redirected from the factory heat exchanger) and inlet/discharge tubes for the fast-rushing air.	All of the stainless boost tubes in the compound-boost setup are numbered and fit without modification. We dig the turbos' low-mount, stealth location. Airflow into each 'charger is filtered with small K&N air filters that fit along both sides of the transmission in small pockets at the front of the chassis (near the steering rack).

 

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The landmark tech effort took place in February 2009 when your tech editor arrived at Gear Heads Automotive and Performance in Arlington, Texas. Company-owner and lead-tuner Travis Franklin was ready and waiting with a mostly new, bone-stock GT500 that we used for the installation and the all-important workout on the rollers of Gear Heads' Dynojet chassis dyno.

Don't just skim through this one. The following photos and captions will let you know the real deal on whether the saying "everything's big in Texas" is true, at least in regard to compound boost and the horsepower it makes on our stock Shelby test 'Stang.

Turbochargers rely on oil for lubrication and cooling. However, with the twin turbos in the GT500 system positioned below the oil pan, there is no way that pressure alone will allow oil draining from the turbos to reach its depository at the passenger-side cam cover. To remedy this situation, Hellion includes an oil-scavenge pump that force-feeds oil through AN -6 rubber hose to its final destination in the engine compartment.	While turbos mounted on the down-low are cool, there's always a concern that they could be damaged by road debris or an obstruction of some sort. On non-lowered 'Stangs, the Hellion twins only take away -inch of ground clearance. However, as a precautionary measure, a bolt-in, stainless-steel turbo shield is included for protection against groundborne enemies.	Hellion relies on Turbosmart's TurboXS race bypass valve, which installs at the side of the final boost before the mass air, to immediately bleed boost pressure out into the atmosphere when the throttle is closed.
A pair of solenoids for the system's optional Turbosmart e-boost 2 electronic boost controller are attached to both framerails and allow total manipulation of the wastegates (and infinitely adjustable boost) by way of a control unit mounted in the cabin. The boost controller will allow Travis to set up custom boost curves that can change the Shelby's demeanor from mild to tire-melting wild in seconds.	A Shelby GT's stock (52-lb/hr) fuel injectors will support approximately 650 rwhp, compound-boosted-or-other, which makes upgrading to Ford Racing Performance Parts new Cobra Jet-spec 80-lb/hr injectors a good idea. The larger squirters increase a stocker's power-making range considerably (to about 800 horses), and definitely will be necessary if making big steam with the 66mm turbos (and a stout fuel system and bottom-end in the engine, of course) is your goal.	Powering the oil-scavenging pump is a plug-and-play deal with the turbo system's supplied wiring harness, which simply taps into a keyed 12V source in the fuse compartment.
In order to complete the coolant-flow circuit for the additional intercooler, a -inch T-fitting and length of hose from the secondary intercooler are plumbed between a Shelby's OEM intercooler and the coolant reservoir.	The rubber AN -6 return hose coming from the oil-scavenging pump is secured to this block, which deposits oil into the passenger-side valve cover.	Before lowering the 'Stang, Travis added a new freer-flowing exhaust system from Magnaflow. The stainless cans are a classy touch for the Shelby, and they greatly improve the exit strategy of the 'Stang's exhaust gases.
Although hidden, the twin-turbo assembly looks wicked below Travis' Shelby. For the record, installing Hellion's compound-boost system on a Shelby GT500 is not something we recommend for the do-it-yourself enthusiast who is limited to working in the driveway or home garage (unless a twin-post hoist is handy). The process definitely requires full access to areas that will be frustratingly difficult to reach if the Shelby is only elevated with jacks and jackstands.	Linking the last boost tube (which routes through a natural opening in the driver-side front of the car), Hellion's polished mass air cylinder and the intake tube are the final stages of plumbing required for the compound-boost system's airstream. All of the necessary silicone couplers and clamps for this step are included.

 

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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 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.

	Baseline			Turbo 1			Turbo 2			Difference
RPM	HP	TQ	A/F	HP	TQ	A/F	HP	TQ	A/F	HP	TQ
5,000	386.56	406.06	11.46	643.87	676.32	10.64	646.36	678.99	10.64	259.80	272.93
5,200	393.45	397.39	11.34	657.23	663.81	10.58	666.71	673.37	11.04	273.26	275.98
5,400	401.07	390.09	11.36	671.53	653.17	10.51	678.04	659.47	11.15	276.97	269.38
5,600	403.15	378.11	11.38	681.70	639.41	10.84	691.18	648.27	11.04	288.03	270.16
5,800	410.29	371.53	11.40	699.83	633.76	11.05	697.25	631.41	11.14	286.96	259.88
6,000	403.05	352.83	11.40	699.35	612.18	10.95	700.63	618.47	11.28	297.58	265.64
6,200	n/a	n/a	n/a	688.07	592.43	11.41	688.39	583.17	11.42	688.39	583.17
6,400	n/a	n/a	n/a	683.91	584.27	0.00	637.65	523.58	12.24	637.65	523.58

Ford Racing Performance Parts www.fordracingparts.com	Magnaflow www.magnaflow.com
Gear Heads Automotive and Performance www.gearheadsperformance.com	SCT www.sctflash.com
Hellion Power Systems www.hellionpowersystems.com	Turbosmart USA www.turbosmartonline.com