Testing Fleece Performance Engineering’s 63mm VNT Cheetah for 6.7L Fords


With the clean diesel era now in full swing, enthusiasts are beginning to embrace emissions-compliant performance. After all, most of us don’t want to blatantly void the warranty on our $80,000 trucks, or go tearing into a brand-new vehicle. Thankfully, fears of trashing the diesel particulate filter and blowing through gallon after gallon of DEF have begun to subside—and in the case of this article, it’s been proven that the 6.7L Power Stroke can support 580 rwhp with the factory emissions systems in place. The hidden benefit of making DPF-on modifications is that no one else will expect your truck to run so strong. The modern diesel sleeper is a smokeless truck. They’ll never see it coming.

Thanks to a traditional single-compressor-wheel turbo and higher-volume CP4.2 injection pump being added in ’15, Ford’s 6.7L Power Stroke not only became more reliable; it turned out more power, too. On ’17 and newer models, 380-390 hp and 850-860 lb-ft of torque makes it to the wheels in stock form.
After clearing 384 hp and 861 lb-ft of torque aboard DC Chassis Dyno’s Dynojet 224 xLC, Fleece’s ’18 F-350 was interfaced with a 150hp, emissions-on tune via EZ Lynk. With the custom tune uploaded, boost pressure jumped to 32 psi and the dually laid down a solid 538 hp and 1,221 lb-ft at the wheels. Throughout all of its testing aboard DC’s load-cell chassis dyno, the truck would be run in manual mode in fifth gear.
No, the factory dual-outlet tip hasn’t been reattached to an aftermarket exhaust system. This truck is sporting 100 percent of its factory emissions equipment (even EGR). If Fleece’s tune-only number of 538 hp proves anything, it’s that the DPF is nowhere near as restrictive as most enthusiasts tend to believe it is.

During in-house testing of their own ’18 F-350, the folks at Fleece Performance Engineering discovered that custom tuning could push the new Fords into the 540hp range—but they also knew more power could be gleaned from added airflow. And since Fleece is in the business of building high-flow, direct-replacement variable-geometry turbochargers—namely the renowned VNT Cheetah line—the crew set about designing a drop-in unit for the 6.7L Power Stroke. To see the finished product installed and tested we trekked over to Fleece’s Brownsburg, Indiana, facility. By the end of the day the company’s tuned, emissions-friendly dually would pick up another 40 rwhp with the 63mm Cheetah in the mix.

If you’re looking to give your tuned 6.7L Ford a competitive edge, this stealthy turbo upgrade is just right for you.

Like the rest of Fleece’s VNT Cheetah product line, the 63mm version for the 6.7L Power Stroke is a direct drop-in replacement, and its retention of the factory compressor and exhaust housings preserves its stock appearance. On the performance front, the Cheetah offers quick, factory-like spool-up, yet flows enough air at high rpm to support 650 rwhp.
A modified compressor housing accepts a Fleece-engineered forged milled wheel (FMW) compressor wheel with a 63mm inducer. The FMW compressor was chosen for its improved durability over billet aluminum and cast offerings. From a competition standpoint, the 63mm inducer meets both 2.5-inch inducer restrictions and stock-appearing rules typically mandated in Work Stock type pulling classes.
With a larger rotating assembly, Fleece adds durability by including a 360-degree thrust bearing in the center cartridge. The bearing provides for full lubrication around the circumference of the thrust collar, rather than 75% of it (via the factory 270-degree thrust bearing).
On the drive side of the Cheetah, a 10-blade turbine wheel with a 66mm exducer is utilized. The larger-than-stock turbine provides vastly improved flow at higher rpm, but thanks to the variable geometry design of the factory-based Garrett GT37, low-rpm response isn’t sacrificed in the least. In fact, when combined with precise custom tuning (with optimized vane functionality), the torque curve is broader than what the factory turbo offers.
The job of tearing into the 6.7L Ford and replacing the stock turbo was left in the hands of Fleece’s lead technician, Jake Richards. First things first, Richards drained both cooling systems (the primary system is dedicated for the engine, while the secondary system is used for the water-to-air intercooler, EGR system, and transmission and fuel coolers). The low-mile coolant would be reused later.
After draining both cooling systems, Richards moved on to the removal of the factory air intake, intercooler pipes, throttle valve, and the upper and lower intake manifold. From there, the driver-side up-pipe was loosened, while the passenger-side up-pipe and the downpipe were removed.
With its coolant lines, oil lines and all four pedestal bolts removed, the factory turbo was ready to be pulled off the engine. After manhandling the turbo forward in the lifter valley in order to clear the cowl, Richards was able to hoist the factory Garrett up and out of the way.
Once the stock turbo had been pulled, Richards made quick work of separating it from the pedestal. After being cleaned up and hit with a coat of black paint, the factory pedestal would be swapped over to the Cheetah charger.

The modern diesel sleeper is a smokeless truck. They’ll never see it coming.

Beginning with ’17 model year engines, Ford began using a small oil filter that protrudes into both the turbocharger’s center cartridge and the pedestal. Equipped with a tiny internal screen, it serves as an added insurance measure against debris from the block making its way into the turbo’s oil supply circuit.
Due to corrosion and constant heating and cooling cycles, the exhaust manifold nuts can be a hassle to break loose and can also cause damage to the exhaust manifold studs during removal. On every 6.7L Power Stroke he encounters, Richards chases the threads of the exhaust manifold studs to clean them up and starts over with fresh gaskets and nuts.
With the turbo pedestal torqued to the Cheetah, Richards finagled the new charger into the stock location. While installing a turbo is still a tight fit on the ’15 and newer trucks, clearance issues are nowhere near as bad as they were on the ’11-14 trucks equipped with the factory (dual-inlet) Garrett GT32 SST.
According to Richards, the hardest part of performing a turbo swap on a 6.7L Power Stroke boils down to the lack of work space between the engine and the firewall. In this photo you can see that the driver-side up-pipe (which was only loosened, not removed, during the install) was connected prior to the downpipe.
Retention of the factory turbocharger’s exhaust housing also ensures that the OEM two-piece downpipe can be retained. With a helping hand pushing up on the downpipe from underneath the truck, Richards was able to mate the downpipe flush with the turbo’s exhaust housing outlet and reinstall its respective V-band clamp.
Once the downpipe was secured at the turbo and at the mounting bracket further down along the firewall, it was time to reinstall the passenger-side up-pipe. Just like on the ’15-17 engines, provisions exist in this up-pipe for both an exhaust backpressure sensor tube and an EGT sensor.
After the VGT solenoid was plugged back in, Richards moved on to reinstalling the cast aluminum lower intake manifold assembly. Then the crankcase breather hose would be reattached.
Next, the factory upper intake manifold was set back into place. The plastic upper manifold, which routes air from the lower intake into the valve covers/intakes, makes use of internal air mufflers specifically intended to reduce intake noise. Retention of the upper intake assembly in conjunction with an aftermarket turbo is a good option for those looking to quell excessive turbo whistle.
With the hot- and cold-side intercooler pipes back in place and the EGR tubes reconnected to the EGR cooler and lower intake manifold, the install was nearing completion. The last major item to be reinstalled would be the factory air intake assembly.
Before the truck could be fired up, Richards topped off both cooling systems. To make sure no air pockets made it into the cooling system, a vacuum purge and refill kit was used.
Like it never even happened. Thanks to the upper intake manifold and the rest of the jam-packed engine bay on the new Super Duty, there is no visual way to tell the truck has been graced with the 63mm Cheetah. With everything buttoned up it was time to start the truck, give everything a once-over for leaks, and head back to the dyno.
As soon as the dually was once again strapped to the Dynojet at DC Chassis Dyno, the guys at Fleece made sure the same unaltered tune was uploaded to the PCM. This was done by opening the EZ Lynk Auto Agent app and locating the 150hp file that yielded the truck’s tune-only 538hp number.
In a matter of seconds, the tuning file was located and less than five minutes later the upload was complete. To record and later analyze the truck’s performance, every pull on the dyno was data logged as well.
Picking up a solid 40 hp over its tune-only number, the truck’s power jumped to 579 hp at the wheels. With the higher-flowing Cheetah turbo in the mix, boost improved from 32 psi to 40 psi—perfectly within the turbo’s safe zone.
During each dyno run, boost peaked at the aforementioned 40 psi and rail held strong at 29,000 psi. And—although the truck felt plenty strong to us—the folks at Fleece assured us that more fine-tuning of the turbo’s vane positioning (via tuning) would soon be underway, which will only broaden the truck’s torque curve. We look forward to seeing their finished data. In the meantime, the truck’s apples-to-apples, 40hp gain with the Cheetah seemed pretty impressive to us.


DC Chassis Dyno

EZ Lynk

Fleece Performance Engineering

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