The Exhaust-Powered Turbine
Out of the box, the Hellion turbo kit made 11 psi, 487 peak rear-wheel horsepower, and 492 lb-ft peak rear-wheel torque. A Turbo People boost controller was turned a few clicks, and peak boost jumped to 13.7 psi, while the power shot up to 521 rwhp and 497 rwtq. Spetter once again turned up the boost, working under strict orders from car owner Billy Sorby, and the power increased dramatically to 570 rwhp and 561 rwtq. This is a stock engine, and it probably won't last too long at that power level. Spetter backed it down so Sorby could cruise the streets and not worry about tossing the rods out of the engine if he romps on it.
Turbochargers have been the source of a lot of attention lately, especially due to their contributions to crazy dragstrip performances in the past few seasons of street legal drag racing. One of the many companies in the marketplace providing turbo kits for Mustangs is Hellion Power Systems. Over the years, several manufacturers have streamlined turbo kits to where purchasing them via mail-order is a reality. In the early years of 5-liter performance, only one or two companies were capable of and successful at shipping a turbo kit. These days, there are several companies that offer complete packages. Hellion goes one step further, though, by shipping the system within 24 hours.
We worked with John Urist and his Hellion brand before when we installed Hellion's Fox-body and '03-'04 Cobra systems. Both were easy to bolt on and made great power on the dyno. The latest creation is the S197 turbo package, and this time we volunteered Billy Sorby's '06 Mustang Saleen. Billy and his brother Bryan compete in NMRA Super Street Outlaw with their red notchback. Their legendary race car was the first nitrous SSO car to break into the sevens, so having a quick street car is a priority to these guys. Urist talked them into adding a turbo, and we followed along with our cameras, capturing the ins and outs of the setup.
A turbocharger setup might make boost, but it is way different than the supercharger system. Everything from installation, to mounting, to tuning is vastly different than the blower. A turbocharger uses exhaust gases to spin an impeller wheel in the exhaust side of the turbo. That wheel is attached to a shaft, which turns the impeller on the inlet side of the turbocharger. The inlet side of the compressor is similar to the supercharger in that air is sucked into the housing via the impeller fins, pressurized in the scroll, and then discharged to the engine. The headers or exhaust manifolds are connected using a crossover pipe, and it usually merges into one pipe and the turbo is mounted on top of it. Most common turbo placement is somewhere in front of the engine, but some kits relocate the turbo to the fender, the front bumper, or in one case, the rear bumper area.
The front-mount intercooler is intimidating looking. It is the only clue that gives away that this S281 has something lurking the hood. We nicknamed the car "Darth Vader" for its appearance and ability to kick ass on the street. With the boost turned up to nearly 18 psi, the Saleen laid down the gauntlet with 570 rwhp and 561 rwtq.
Most people understand the inlet side of a turbo rather easily, and the measurements like 62 mm, 76 mm, 106 mm, and so on are the inlet holes of the turbo and thus their most common classification. Equally important is the exhaust side of the compressor, which is the least understood part of the turbo. Most people look at the exhaust wheel, noticing that it appears to be similar in design to an impeller. The uninformed think the exhaust wheel is spun by the exhaust gases flowing over the fins, but that is completely inaccurate. The wheel does not act like a windmill and spin when the exhaust flows over it. Thermal expansion is what drives the exhaust wheel in a turbocharger.
Some systems on the market continue to utilize the factory exhaust manifolds in high-horsepower applications because the amount of exhaust flow isn't as important as perceived. The easiest and simplest way to explain thermal expansion is using the candle trick. Hold a candle under an exhaust wheel tip, and the expanded gases will spin it. Think of the exhaust gases trapped in the exhaust housing trying to expand, and that is what drives the wheel. The header shape does affect the turbo, but in applications less than 1,000 hp, they are not as critical.
The exhaust side housing and wheel is where the less experienced enthusiast can go wrong. Too small of a housing and the turbo will have excessive backpressure resulting in a loss of performance. Backpressure is the opposite of boost and the gases will push past the wheel if too much of it is in the exhaust housing. If the exhaust housing is too big, then spool-up time will be increased dramatically. Hellion provides a Turbonetics 62mm turbo that has been spec'd out for this application, taking the guesswork out of selecting the proper compressor.
The JLT cold-air kit was removed for the installation. Sorby had added Ford Racing Performance Parts shorty headers to the otherwise stock Saleen Mustang. The car comes standard with a better exhaust system, an SFI-approved balancer, and a host of suspension upgrades. | 
The impeller measures 62mm and is capable of supporting power in the low-600hp range. It was right where we shut down the dyno pulls for fear of exploding the stock engine. Uncorrected output was a demented 604 rwhp, which was corrected down by Standard Correction to then read 570 rwhp. Crazy Horse's dyno is located across the street from a water outlet that leads to the Atlantic Ocean, so we were definitely at sea level. The air temp was also in the low 40s, and corrected altitude was well below sea level. A quick workup on the calculator had this engine making 690-700 hp at the flywheel. | 
Here is the turbo impeller exposed with the scroll removed. Notice the variations in blade angle, and the extreme leading edges on the leading impeller blades. |