Modern diesel engines are impressive animals. Simply adding a programmer can boost performance by nearly triple digits, which ultimately leads to the insatiable need for even more power. The next logical step for the diesel junkie on the prowl for power is an upgraded turbocharger. However, upgrading to a different-than-stock turbo can snowball into quite the can of worms. What’s a person to do whose engine needs more airflow without tearing apart the engine bay? Enter the Cheetah.
Born in the sport of sled pulling, the brains at Fleece Performance Engineering in Brownsburg, Indiana, have perfected the art of gutting factory chargers and filling them with upsized compressor and turbine wheels. The Cheetah, or “cheater” turbo, filled a niche for those wishing to compete in the local sled pulls in classes that required factory-appearing turbos or those with inlet size restrictions. These turbos allow for increased fueling and thus more power than otherwise factory-equipped trucks. What was born in competition has now turned into a huge market for the average diesel enthusiast.
From the onset of our LB7 Duramax build, we set a power goal of a modest 600 rear-wheel horsepower while maintaining a factory appearance under the hood. We’re building a sleeper, if you will—a truck that’s as unassuming at the track as it is at a certain government inspection facility. Fleece’s LB7 Cheetah checked all the necessary boxes, so we hopped a plane to Indiana to watch the technicians transform our factory IHI turbocharger into a hard-charging Cheetah.
Design and Engineering
| What started innocently enough has evolved into a modern work of art. Engineering is done by computer before the first shaving of metal is ever removed. This helps to reduce a lot of guesswork and remove a large degree of human error involved in the traditional research and development phase of products such as this.
| Once the program is created and the first parts come off the CNCs, they are meticulously checked and double-checked. While the computer can get the parts mostly perfect, it still takes a human eye to verify what is coming out is correct. After all, Fleece is perfecting the art of modifying parts that can be more than 20 years old and may not have adhered to the strictest of tolerances when they were built.
| The final step in implementing a new Cheetah design involves dissection. Seen here is a cross section of an LB7 turbo that’s been cut in half to ensure the compressor-wheel-to-housing clearances are perfect.
| Since the Cheetah turbo is designed to utilize the factory turbo housing, a good supply of usable cores is necessary to keep them flowing. Fleece builds Cheetahs for ’94-to-current Cummins, ’01-to-’10 Duramax, and ’03-to-’07 Power Stroke engines.
| The process of unleashing a Cheetah begins with disassembly of the core turbo. Isaac Hedges makes short work of stripping down the factory IHI turbo from our ’02 LB7 Duramax, starting with removing the oil drain tube.
| Next the turbine housing is separated from the center cartridge. After years of use, along with the rough life a turbocharger lives anyway, it’s not surprising that a bit of force is needed to separate the two.
| With the turbine housing removed, Isaac turns his attention to the compressor side by first removing the accessory brackets and wastegate actuator. The cartridge is then removed and discarded.
| Once apart, the compressor and turbine housings are loaded into a high-temperature parts washer and given a thorough scrubbing to remove the baked-on oil, dirt, and grime. Think of it as the ultimate man’s dishwasher.
| After all the grime is removed, the housings are loaded into a steel abrader. This process removes the years of rust and corrosion, leaving the housings in like-new condition and ready to move on to the machining process.
| The IHI turbo used by the LB7 Duramax uses an external wastegate actuator, which is reused by Fleece for the Cheetah turbo. Each actuator is tested to ensure proper, leak-free function by pressurizing to 50 psi—about double what it sees during use. If it checks out as good, it is reused; if not, it is replaced.
| Since our wastegate actuator passed the functionality test, Isaac gives it a good sandblasting to clean up the exterior before a fresh coat of paint and reinstallation on the finished turbo. Before you ask, the pressure orifice is plugged before blasting and painting to prevent any foreign debris from contaminating the diaphragm.
| Fleece Performance Lb7 Duramax Cheetah Turbo Build Clean Up
| All the machine work necessary to turn a factory turbo into a Cheetah is done in-house at Fleece’s facility in Indiana. Marc Beaman is seen here programing one of Fleece’s HAAS CNC lathes. The company also employs a fleet of CNC mills along with the lathes, having nearly unmatched machining capabilities for a company of its size.
| The factory compressor housing is machined to accept the new BorgWarner S300-based center cartridge. Clearance is also made for the charger’s larger compressor wheel. The inside surface receives a quick polish before being called finished.
| Fleece Performance Lb7 Duramax Cheetah Turbo Build Clearance
| (right) Before (left) After
| (right) Before (left) After
Along with the intake housing, the turbo mouthpiece is also machined for better flow. A custom jig allows the oddly shaped unit to be spun in the company’s CNC lathe. The end result is a piece that flows much better than factory and has been shown to produce double-digit horsepower increases.
| The turbine housing also receives a bit of machine work, which is necessary to accept the S300 cartridge. All told, each turbo receives about 30 minutes of automated machine work.
| To ensure the long, trouble-free life of each turbocharger it builds, Fleece balances every compressor wheel that comes through the shop. The compressor wheels are spun on a precision balancer that shows exactly where and how much material needs to be added or removed in order to have a perfectly balanced wheel. By not relying on the manufacturer or a third party, Fleece maintains precise control over the quality of the finished product.
| Fleece Performance Lb7 Duramax Cheetah Turbo Build Balancing
| With all the machine work complete and parts painted, the Cheetah turbo is ready for assembly. The turbocharger is a relatively simple machine at its core. However, correct assembly takes a bit of specialized knowledge.
| The first step in assembling the turbo is building the S300 cartridge. The cartridge’s job is to act as the bearing carrier for the shaft that connects the turbine and compressor wheels. A pair of journal bearings, a 270-degree thrust bearing, and an array of O-rings are installed and held in place with a set of snap rings.
| Fleece Performance Lb7 Duramax Cheetah Turbo Build Assembly
| Fleece Performance Lb7 Duramax Cheetah Turbo Build Assembly Cartridge
| Next, the high-flow turbine wheel is installed. The turbine wheel comes balanced at the factory and preinstalled on the shaft, making this a simple slip-in procedure.
| The compressor wheel is installed next. The wheel is first heated with a torch, and then slowly spun down into position on the shaft. Using this method of installation ensures the compressor wheel is perfectly centered on the shaft.
| Once the compressor wheel slides into place, the retaining nut is torqued to spec to ensure the wheel is completely seated. The nut is then backed off while the wheel cools down, then thread-locking compound is applied and the nut torqued to its final tightness.
| Fleece’s LB7 Cheetah turbo uses a custom 62mm aluminum forged milled wheel (FMW) compressor. This is the fancy way of saying it’s a billet compressor wheel.
| With the compressor wheel in place, the compressor housing can be installed. A bead of silicone ensures a complete seal while six Allen head bolts secure it from the rear.
| One final tolerance check is performed before the turbo can be called complete. If everything checks out, the charger is boxed up and shipped out to its happy new home.
| Once assembled, it is incredibly difficult for the untrained eye to discern a difference between what was once the factory turbocharger and what is now a Fleece Performance Cheetah.