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A Party on Wheels--Turbine Wheels, That Is
Hellion Power Systems Threw a Bash for Four-Valve Cobras, and 847 friends showed up at the tires.
Back in the November '05 issue, we covered the installation of the Hellion Power System 5-liter turbo kit. During that install, we kept glancing to the other side of the shop to check out what the Hellion crew was brewing up. It turned out Hellion's John Urist was R&D'ing the company's kit for '99 and '01 and '03-'04 SVT Cobras, plus '03-'04 Mach 1s. The kit was released to the public shortly after our story hit the press. It didn't take a tarot card reader to tell us a trip back to the Albuquerque, New Mexico, facility was in our future.
Initially, we had planned to install a Hellion turbo kit on a '99 Cobra, but that fell apart when the car was sold. So we decided to use Nate Phillips' '04 Cobra as our test vehicle. Because of the car's stout engine combination, this Hellion kit included an upgraded turbocharger, meaning we could really turn up the power without fear of breaking anything. The Cobra and Mach 1 kits are similar, so installation is virtually identical. Major differences between them are fuel supply components, a couple of pipes, and the turbo unit. Those with a built Four-Valve engine in their '99/'01 Cobra or Mach 1 can upgrade to the '03-'04 Cobra kit and see similar horsepower numbers with the larger 76mm Turbonetics turbo.
Hellion informed us that the '99/'01 Cobra kit produces between 400 and 450 hp at the tires, with 8-10 psi of boost. The 62mm turbo will generate enough airflow to make 550 rwhp when turned up. The limiting factor, however, is the factory internals. It's easy to lose your self-control because more boost is only a twist of a knob away. Just remember--would you put the smallest pulley on the supercharger if your engine were stock? Nope. So follow the same restraint when playing with turbos. It can get out of hand rather quickly.
While the '99/'01 kit is a direct bolt-on, the '03-'04 SVT setup is more of a tuner-style kit. Urist explained the '03-'04 Cobra kit is a beast of another kind with its 76mm turbocharger. "A full-bodied Cobra, a legit street car, with a straight axle and good suspension setup can run 9.90s at over 140 mph with this kit. I know because we have had customers run those times." He also reminded us that the engine was stock save for the turbo setup and intake.
Once '03-'04 Cobra owners dump the stock Eaton blower, they will need to buy a '99/'01 Cobra intake or an '03-'04 Mach 1 intake. The piping is a little different between the turbo systems due to the physical size of each compressor unit. Larger fuel injectors are available in the '03-'04 kit, but it does not include a fuel pump or lines.
The turbo system was laid out on the workbench, and one look at everything reveals the same quality and finish as the 5-liter setup. The hot side of the turbo system (the exhaust side) is done in stainless steel and carries a lifetime warranty. The cold side (compressor side of the turbo) is stainless piping and comes polished. Every nut and bolt is included in the kit, and the Turbonetics 76mm turbo was specifically designed for this application. More on that later.
We also liked the detailed instruction manual and the fact there is no cutting or welding required. However, the K-member and A-arms must be replaced to make room for piping and such. This definitely ups the overall expense, but it's nothing unusual for turbo applications on modular Mustangs.
Installation was straightforward and took us a little more than a day to install the turbo. Our test vehicle already had the K-member and A-arms installed, so that cut down on time. Urist estimates anywhere from two to five days for a full installation depending on mechanical experience and how quickly you work. Our install guys weren't a Top Fuel crew, but they certainly didn't work at a snail's pace.
There are a few things to remember when utilizing turbo power, and one of the most important suggestions we can give you is that bigger isn't always better. Obviously, making big horsepower is the ultimate goal with our Mustangs, but a huge turbocharger may only make awesome peak numbers. Who wants to wait all day for the turbo to spool up? Oftentimes, the power is not useable in real driving conditions. What sounds good on paper, or the Internet, isn't always good in the real world. The goal for a street car should be a long, broad torque curve. That will certainly make everyday driving enjoyable. It also helps big time when you happen to run into some of the local competition on the street.
Our test vehicle has a stock '04 Cobra 4.6 engine (281 ci). That size engine reacts nicely to the 76mm turbo supplied in the kit. It makes great peak horsepower, but still builds boost in the lower rpm ranges. One look at the power curves in this story shows how broad the torque and horsepower curves are. "It took some time to work with Turbonetics to find the right turbine/ exhaust side of the turbo to eliminate lag and maximize peak horsepower," Urist says.
Turbos are essentially two different halves--a compressor side and a turbine side. Often, people look only at the compressor side of things, i.e. 76mm turbo, 91mm turbo, or 101mm turbo. It is the exhaust/turbine side that drives the compressor wheel. Think of the turbine side as the pulley in a blower setup. The hot exhaust gases expand in the turbine housing to help spin the wheel. That drives a shaft that spins the impeller on the compressor side. It is not entirely exhaust flow that spins the wheel but rather expanding exhaust gases. This is known as thermal expansion.
When selecting a turbocharger for any engine, being able to turn the exhaust wheel efficiently is just as important as what the compressor produces at peak operating impeller speeds. The bigger the exhaust housing, the faster it spins at higher rpm, but if matched improperly to the engine, low-end compressor speed will suffer. Too small and peak horsepower suffers miserably. It is a balancing act between the turbine and compressor wheels for a given combination.
While the car was on the dyno, we tested a few different compressors and exhaust housings just to see the difference in power. A more efficient exhaust housing netted the same horsepower results but at a lower boost level and less fuel consumption. Going up one more size resulted in excessive boost lag--remember our test subject had a 281ci engine. It goes to show how matching the compressor and turbine is critical for different applications. Our test car made 847 hp to the tires at 24 psi of boost with the 76mm turbo and 16 degrees of timing. This was also with stock exhaust manifolds. Urist says the exhaust manifolds have not been a restriction in power with the 76mm turbo. He has taken the turbo unit to its maximum output, and it was the compressor side that maxed out before the exhaust system was a problem.
A little curiosity never killed anyone, and we asked what it would take to crank out 900 or even 1,000 hp at the tires. Urist got a look in his eye and asked if we really wanted to make 1,000 to the tire. He did remind us that was eight-second power, and was that necessary for the street? We're horsepower junkies--of course we need it. We have a feeling Hellion has something brewing to satisfy our desires.
Nate Phillips' '04 SVT Cobra At A Glance
Surprisingly, the car remains mostly stock, and Phillips has upgraded parts only as needed. We want to point out that the stock exhaust manifolds have been left in place, but the Hellion kit will work with aftermarket shorty headers. The IRS remains stock and hasn't caused any problems, despite rolling around on Mickey Thompson Drag Radials. The long life is attributed to no drag racing-like launches at the track or on the street.
The fuel system was in dire need of attention thanks to the planned turbo installation. A pair of Lincoln Aviator pumps, rated at 270 lph, was installed as well as a -8 feed line and prototype Hellion fuel rails. DiabloSport tuning was utilized to tune the beast, and Phillips chose to use a chip instead of reflashing the computer. The stock MAF sensor was used, but is aided by a MAFia. The DiabloSport MAFia recalibrates the MAF sensor signal enabling use in high-horsepower applications. It also recalibrates for larger sized injectors--in this case we were using 60-pound high-impedance fuel injectors.
The transmission is holding up just fine, but the clutch is a different story. The stock unit is long gone. Urist joked that Hellion was also a McLeod dealer. A McLeod clutch, pressure plate, and lightweight flywheel transfer the power into the six-speed transmission.
All '03-'04 Cobras are notorious for their low-end torque, thanks to the factory-supplied Eaton blowers. So what should be expected from the Hellion turbo kit? For starters, turbos have always been known for the low-end grunt and neverending torque curve. With that said, it may give up something in the 1,000- and low-2,000-rpm ranges to the Roots-style blowers. But once the turbo comes on, the power can only be described as demented. It just keeps pulling right up to redline. If the engine could rev higher, there's no doubt the turbo would continue to shove you into the seat harder.
Our experience in this car was interesting, to say the least. The tests were made from a Second-gear roll. As soon as the throttle is slammed wide open, a few things happen. Your mind instantly thinks this isn't so bad. A nanosecond after that, the boost gauge sweeps past 20 psi and your eyeballs smash into the frontal lobes of your brain. The boost gauge hits 25 psi instantly and the rpm continues to climb. The 6,500-rpm shift point comes up quickly. There is a brief pause in the madness because of the granny shift, and then it starts all over again when you go back to WOT. Boost drop is minimal on the gearshift, despite the easy shifting methods.
Third gear offers a bigger load on the engine, so the boost gauge surges toward 27 psi. We are not sure where the boost gauge needle went from there because we tried not to take our eyes off the road at these speeds. You don't realize how fast you're going because everything is a blur, and of course the engine is screaming and the turbo is whistling. As your foot comes off the pedal at the top of Third gear, the realiza-tion that you are over 120 mph sets in. Cool.
Phillips said if we had slammed the transmission into Fourth, we would have seen 29 or 30 psi of boost on the gauge. We made 847 on the dyno at 24 psi, so conventional thinking would push the horsepower on the street a bit higher. The power is smooth and fun. And let's just say there's an LS1 Camaro SS owner that isn't too happy right now.