Stacking Compounds on a Factory 6.7L Power Stroke Bottom End
Our quest to push a bone-stock ’17 6.7L Power Stroke long-block beyond 800-rwhp kick-started a while back with the addition of 60-percent over injectors and a 10mm stroker CP4.2 from Exergy Performance. Now, we’re moving on to the air side of the equation. But instead of playing it safe by running a big single, we’re putting Ford’s “updated” connecting rods to the ultimate test by way of No Limit Fabrication’s compound turbo system. Chosen for its superb fit and finish, great drivability, and horsepower potential, No Limit’s kit combines a Precision atmosphere charger with a stock-location VGT. In our case, we opted for an 82mm Precision out front (over the kit’s standard 76mm Precision), and a Fleece Performance Engineering 63mm FMW Cheetah in the valley.
In preparation for the additional boost and the inevitable cylinder pressure that comes with it, we performed several peace-of-mind modifications, too. First, and because the 6.7L’s crank gear has been known to slip with big power in the mix, we pulled the front cover and welded the crank gear to the crankshaft. While we had access to it, the cam gear also received two welds. Then, in an effort to make sure the engine always sees adequate oil pressure at high load, H&S Motorsports’ billet oil pressure regulator was installed. Assured the crank and cam gears aren’t going anywhere, and that 60 to 80-psi of oil pressure will be on tap when it’s needed most, it’s time to see what the factory long-block is made of.
If the engine survives a trip to the dyno, we’ll have some horsepower numbers for you in Part 3. Stay tuned.
Flirting with Disaster
Since its inception, the 6.7L Power Stroke rods have been a weak link any time they’ve been pushed into 700-rwhp territory. Add big fuel and a compound turbo system that boasts a VGT in the valley and you’ll see the kind of cylinder pressure (i.e. low-end torque) that’s known to bend the factory units. While the rods in Job 2 ’17 model year and newer engines are believed by some to be stronger (they make use of a 1mm larger wrist pin), the verdict is still out as to how much power they can withstand. In short, we know we’re asking for trouble in putting this series together. Don’t try this at home unless you have plans to run a built engine eventually, or plan to detune things to a safer power level.
No Limit Fabrication’s highly-refined compound system allows you to add a sizeable atmosphere (low-pressure) turbo to your ’11-present 6.7L Power Stroke. The company sources its chargers from industry titan, Precision Turbo & Engine, with Precision’s 76mm GEN2 PT7685 CEA coming standard. In our case, we opted for the 82mm version, along with a factory-based VGT upgrade: the 63mm Cheetah from Fleece Performance Engineering. Key supporting components in the No Limit kit include a heavy-duty atmosphere turbo mount, two-piece stainless steel hot-pipe, two-piece 4-inch downpipe, a cold air intake, and a battery relocation tray. As you can see, we also added No Limit’s optional hot and cold-side intake piping kit to the list.
We used the installation of the No Limit compounds as an opportune time to upgrade intercoolers. For its ability to flow 22-percent more air than stock and its rigid, cast-aluminum end tank construction, Mishimoto’s performance air-to-water drop-in unit checked all the boxes for us. Like the intake piping, compressor housings, and battery tray, the Mishimoto intercooler was also sent in for Black Cherry powder coating prior to being installed.
Before we got started bolting the No Limit compound kit in place, we drained the engine oil (as well as both cooling systems) and pulled the factory oil pan. It was here that we confirmed our 6.7L Power Stroke did in fact leave the assembly line with the updated, Job 2 connecting rods. Then, the No Limit billet-aluminum oil pan was bolted in place using the stainless steel bolts and O-ring seal it ships with.
Not only does No Limit’s billet oil pan accommodate the atmosphere turbo’s oil drain, but it adds three quarts of oil to the 6.7L Power Stroke’s overall capacity, along with a magnetic drain plug. When it’s ordered in conjunction with the compound turbo system, No Limit offers its pan at a discounted price ($629).
Slipping the crank gear and not having enough oil pressure at full load and high rpm are major concerns for 6.7L Power Stroke owners, but removing the front cover and addressing these issues with the engine still in the truck isn’t for the faint of heart. But while it was a royal pain to put back on, pulling the front cover allowed us to TIG-weld the crank gear to the crankshaft in three places, the cam gear to the camshaft in two spots, and install H&S Motorsport’s billet oil pressure regulator. Addressing these potential weak links definitely improves the factory rotating assembly’s ability to hold up to big horsepower.
Across all niches of motorsports, Precision turbochargers are the cream of the crop, and the GEN2 PT8285 CEA is no different. It sports a 4-5/8-inch outer diameter V-band discharge compressor cover and utilizes an air-cooled, dual ceramic ball-bearing center cartridge. On the exhaust side, you’ll find an 11-blade turbine wheel with an 85mm exducer inside a 1.12 A/R non-wastegated housing with a T4 flange.
Capable of supporting 1,325 hp, the Precision GEN2 PT8285 CEA moves plenty of air. Its Competition Engineered Aerodynamics (CEA) 82mm inducer compressor wheel is machined from a 2618 aluminum forging, which is said to offer the quick transient response this charger is known for.
To uncork the potential of the high-pressure turbo in our combination, the factory charger was ditched in favor of Fleece Performance Engineering’s hot-selling 63mm FMW Cheetah. Based on the OEM Garrett, it bolts in the exact same location and retains variable geometry functionality. Airflow is opened up via Fleece’s 63mm inducer forged milled compressor wheel and the Cheetah is rated for 650-rwhp as a single. In compound arrangements, it has proven capable of supporting well north of 750 hp.
For significantly improved exhaust flow, the Cheetah makes use of a 10-blade, 66mm turbine wheel (vs. the 13-blade, 62mm version that came stock). As you can see, the Cheetah retains the factory exhaust housing, which means the up-pipe connection points stay the same. The OEM compressor housing (albeit machined to accept the larger, 63mm FMW wheel) and pedestal are still employed as well.
Under the hood, the turbo install picked up right where we left off in Part 1, with all intake openings taped up and the factory turbo already pulled (Fleece requires a core with each Cheetah it sells, so we shipped ours out immediately). However, in knowing how close the new downpipe would be to the PCM we had to relocate the driver side-most wiring harnesses toward the passenger side fender, underneath the PCM. Thankfully, Ford supplied plenty of extra wire for these plugs from the factory, so there was no need to tap into them and extend them.
As in any type of add-a-turbo kit, you have to anticipate making a few tweaks to things in order to not only accommodate the new (and larger) turbo, but all of the intake and exhaust plumbing that comes with it. To make way for the Precision charger, we tweaked the A/C lines at the front of the passenger side valve cover toward the driver side.
Not wanting to have to finagle the 4-inch downpipe (which we treated to DEI titanium exhaust wrap) into place after mounting the Precision turbo, it went in first. And to make things as easy as possible, we even held off on setting the Fleece VGT in place until after the downpipe was positioned close to where it would eventually end up. Notice that the heater core hose will route over the top of the downpipe and that the atmosphere turbo mount has been bolted in place on the passenger side valve cover.
In addition to supplying a new turbo pedestal gasket and coolant feed line with the 63mm Cheetah, Fleece also includes a fresh oil screen for the supply port in the pedestal. Should something fail in the engine, this low micron screen will keep debris from making it into the VGT’s center cartridge.
With fresh up-pipe gaskets and the Fleece-supplied pedestal gasket in place, it was time to set the Cheetah on the block. Despite the hulking weight of the turbo (it outweighs the Precision unit, believe it or not), we took care to set the charger correctly the first time. The last thing we wanted to do was nick up or damage the pedestal gasket in any way.
Prior to installing the four turbo pedestal bolts, the top and bottom of each fastener’s threads were hit with a coat of fresh engine oil. This step ensures the most accurate torque possible once they’re tightened up. Then each bolt was installed and tightened to Ford’s 41 ft-lb specification.
The downpipe still loosely in position, the passenger side up-pipe was reinstalled next. We found an extendable mirror extremely handy in checking (and double-checking) the clamp positioning on the up-pipes.
After that, the factory exhaust backpressure sensor was reinstalled in the passenger side up-pipe (top left). This sensor is required for the variable geometry functionality of the Cheetah turbo. Then the new coolant supply line was installed between the Cheetah and coolant crossover. The hard heater core line shown here is what will eventually reconnect with the heater core hose we showed you earlier.
Looking at the clearance between the number 1 cylinder injector harness and the turbine housing side of the downpipe, we decided to custom fit a section of heat insulation to the front corner of the passenger side valve cover. This small addition will keep the injector harness, plug, and the return line from seeing excessive heat in the this vulnerable area.
In the No Limit compound system, the 3-inch hot-pipe comes in two sections. The section shown clamps to the valley charger’s exhaust outlet and loops over the top of it, attaching to the second pipe after clearing the compressor housing. To provide for ample movement and expansion, this section features a heavy-duty bellow.
The second section of the hot-pipe is what connects to the atmosphere turbo—while at the same time tying in to the billet turbo mount that bolts to the passenger side valve cover. To avoid fastener clearance issues when joining the hot-pipe’s flange to the Precision turbo’s T4 inlet, we used studs (and sourced the corresponding nuts needed) on the top two mounting holes, instead of bolts.
With the Precision turbo attached to the hot-pipe, the supplied oil drain was installed in its center cartridge. From there, the atmosphere turbo and hot-pipe were installed as a single assembly, with the turbo first being fastened to the turbo mount using the included bolts and a 5/16-inch Hex bit socket.
After that, the downpipe was clamped to the Precision turbo’s exhaust housing, the heater core lines were reattached, and both hot-pipes were clamped together. In order to clear both the supplied intake Y-pipe and the VGT’s compressor housing, the hot-pipe clamp can really only be oriented as shown.
Before the atmosphere turbo’s compressor housing could be clocked correctly, the supplied reducer boot was installed on the VGT’s compressor inlet and the charge pipe mocked up. The Precision’s V-band compressor outlet and solid mounting point eliminates any possibility of blowing an intercooler boot in this high boost area. Once everything looked good, the compressor housing’s orientation clamp was tightened up for good.
A two-section, high-flow intake Y replaces the upper and lower intake plenums, routing boosted air from the intercooler into the cylinder heads. While the intake Y solid mounts to the passenger side valve cover’s inlet, a silicone boot at the intercooler allows for ample (and necessary) axial movement. A shorter, 90-degree section of pipe spans from the driver side valve cover inlet to the intake Y-pipe.
With fitment issues being non-existent in No Limit’s well-engineered compound system, this piece only adds to the kit’s quality. It’s an HD Quick Release clamp from Vibrant Performance and it provides an air-tight seal while also allowing as much as 12 degrees of axial movement in charge tube piping. Here, it’s being used to connect the No Limit intake Y pipe with the 90-degree intake pipe.
Moving on to the Mishimoto air-to-water intercooler install, the driver side battery tray and degas bottle were first bolted back into place. Then the Mishimoto unit was lowered into the factory location. A direct drop-in replacement for the factory stacked-plate unit, it uses the stock mounting points, accommodates the OEM coolant line, and retains the rolled bead and ribbing present on the factory inlet and outlet (a non-slip surface for intercooler boots).
Utilizing Mishimoto’s CNC-machined, polished-aluminum coupler and No Limit’s supplied intercooler boots and constant-tension T-bolt clamps, the hot-side pipe was installed. After that, the cold-side intercooler pipe and its respective boots and clamps were installed and cinched down.
Once the supplied braided stainless oil feed line was connected to the Precision charger and the oil drain attached at the new oil pan, we set to work adding No Limit’s cold air intake. For its ability to outflow an oiled filter, we opted for the dry aFe filter element No Limit offers.
After installing the lower section of the included downpipe and tying it in with the truck’s existing exhaust system, we double-checked all of our work, tightened everything up, added fresh oil, fuel filters, and topped off both cooling systems with the factory coolant. Then we cycled the ignition and primed the fuel system a handful of times to purge as much air as possible.
This isn’t our first experience with No Limit’s compound turbo system, and thanks to its outstanding fitment, performance potential, and great drivability, it won’t be the last. The combination of Precision’s 82mm atmosphere charger with Fleece’s 63mm Cheetah should not only bring 900-rwhp capability to the table, but superb drivability, a one-of-a-kind whine, and plenty of smiles is expected, too.
Fleece Performance Engineering
No Limit Fabrication
Precision Turbo & Engine
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