Big, streetable horsepower. We all crave it. Deep down, we all want a truck that can run low 11s yet still get us to and from work on a daily basis. The easiest way to make this possible (and not have a laggy truck or a transmission that hates you) is to run a compound turbo arrangement. Thanks to companies like Elite Diesel Engineering, 6.4L Power Stroke owners have the luxury of retaining the factory-based sequential turbo design when the need for added power arises. In short, both turbos can be upsized considerably, with virtually no tradeoff in drivability.
02 Based on the 6.4L engine’s original sequential turbo system design, Elite’s Raw- Power compounds retain a variable geometry, high-pressure charger—albeit with a different compressor housing and wheel. If you look in between the two turbos you’ll see that Elite casts its own intermediate piece, which incorporates a wastegate provision directly into the casting.
For years, Elite has been building compound arrangements based around the 6.4L Power Stroke’s compact factory system for any power level from stock to more than 1,000 hp. To appeal to 6.4L owners on tighter budgets, Elite recently brought its Raw-Power compounds to market. Making use of an 88mm low-pressure turbo for awesome top-end flow and a 63mm VGT high-pressure turbo for ultra-quick bottom end response, this system offers ’08-10 Ford owners the most affordable path to making 900 rwhp in Elite’s catalog.
03 Completely replacing the factory low-pressure turbo is this massive charger from Precision Turbo & Engine. It employs a billet compressor wheel with an 88mm inducer, and features a journal bearing center section with a 360-degree thrust bearing system for optimum durability.04 As mentioned, the high-pressure turbo in the Raw- Power arrangement retains the factory exhaust housing and VGT actuator, but the compressor housing is different (note that your VGT turbo is required as a core item when ordering a Raw-Power kit). An 11-blade, 63mm inducer compressor wheel is used in the new compressor housing, and the turbo’s center section utilizes journal bearings. Also notice that the compressor housing makes use of a map width enhancement groove, unlike the factory unit.05 Another core item Elite requires for its Raw-Power system is the factory turbo base. To make way for the larger 88mm turbo, the integrated low-pressure turbo oil drain of the base must be cut down. The piece on the left represents a stock, unaltered turbo base, while the one on the right illustrates how short the oil drain needs to be. A fresh turbo base gasket was installed in our base prior to it making its way into the lifter valley.06 Elite’s custom-fabricated stainless steel up-pipes feature 0.065-inch wall thickness, heavy-duty expansion bellows, and can be built with provisions for both high-pressure and low-pressure wastegate piping included. In this photo, the driver side up-pipe is pictured on bottom and the passenger side unit up top, both of which have wastegate pipes built into them.07 Opting for what Elite calls its Secondary Underneath Wastegate kit, this pipe spans from the low-pressure turbo’s wastegate to the downpipe. The pipe diverts excess drive pressure away from the low-pressure charger if the need arises, and is actually routed under the transmission bellhousing.08 We’re running two wastegates in our Raw-Power system. Alleviating drive pressure from the high-pressure turbo will be the unit on the left: a 44mm Tial MV-R gate. Because this wastegate will be the more active unit (and constantly exposed to heat), the MV-R was selected for its ability to circulate coolant throughout its actuator top. It will sit just above the driver side up-pipe near the firewall. The second wastegate is a 46mm unit from Precision Turbo & Engine (right), which will keep the low-pressure turbo from seeing excessive drive pressure by allowing exhaust to leave the driver side up-pipe and flow to the downpipe via the aforementioned secondary wastegate pipe.09 Working in conjunction with Elite’s custom up-pipes will be a set of BD Diesel’s 6.0L Power Stroke exhaust manifolds. These heavy-wall, high-silicon ductile iron manifolds outflow the stock 6.4L units and (more importantly) incorporate the elbow transition for the up-pipes cast into them. (Thin-walled up-pipes incorporate this 90-degree transition on stock 6.4L mills, and they often blow out under high heat and/or drive pressure.)10 The last core item in Elite’s Raw-Power system is the driver side rocker box, which must be modified in order to clear the high-pressure turbo’s larger compressor housing. Knowing this ahead of time, we modified our own rocker box prior to sending it off to be powdercoated.11 On the intake side of things, Elite provided a silicone elbow to open up airflow to the 88mm low-pressure charger. The elbow features steel internal reinforcement rings so it won’t collapse under boost. During in-house dyno testing, this elbow alone was good for a 26hp gain (on a 650hp truck) over a popular aftermarket air intake system.12 To clear the low-pressure turbo, the factory intake manifold has to be modified, along with relocating the factory intake air temperature and boost sensors (arrows). You can modify your own, or order one of Elite’s Z-Max or Z-Max Jr. intake manifolds. Because we’re running stock (non-ported) cylinder heads, we opted for the Z-Max Jr., which flows 5% more air than stock (9 cfm) thanks to partial porting and the removal of internal restrictions (namely the bolt bosses).13 All necessary installation hardware is provided in Elite’s Raw-Power system, including the appropriate up-pipe gaskets, T-bolt, V-band, and worm gear clamps, intercooler hoses, and fasteners. Braided oil feed lines which tee together, a fabricated oil drain extension for the low-pressure turbo, oil drain gaskets, and an oil drain gasket adapter (for the low-pressure turbo) were also supplied.14 With the modified turbo oil base installed in the lifter valley, the factory high-pressure turbo oil drain tube and fabricated low-pressure oil drain tube were set in place, followed by the turbochargers. The 100-pound Raw-Power assembly gets anchored to the block via the factory turbo base clamps.
“MAKING USE OF AN 88MM LOW-PRESSURE TURBO FOR AWESOME TOP-END FLOW AND A 63MM VGT HIGH-PRESSURE TURBO FOR ULTRA-QUICK BOTTOM END RESPONSE”
15 Next, the BD 6.0L exhaust manifolds were installed, along with factory Ford exhaust manifold gaskets. We’ll note that the driver side manifold comes with a convenient, pre-drilled port for a pyrometer probe, and that BD treats these manifolds to a corrosion-resistant coating.16 Measuring drive pressure will be vital during testing to ensure the 63mm high-pressure charger survives in this application. Of course, we’ll be putting the exhaust backpressure sensor port (included in Elite’s driver side up-pipe) to good use once the truck is up and running.17 We’ll point out that no exhaust manifold or up-pipe bolts were torqued during the mockup stage, as we wanted to make sure that all components fit and aligned properly first. Once everything was hand-tightened into place, we retraced our steps, snugging up each fastener for the last time.18 Once the up-pipes were secured to the high-pressure turbo collector and exhaust manifolds, we attached the supplied wastegate adapter pipe to the passenger side up-pipe. Then the Tial wastegate was clamped into place, followed by the included wastegate-to-turbo pipe.
WASTEGATE TUNING
Tuning a wastegate is not a set-it-and-go type of proposition—it takes time to find an ideal boost-to-drive pressure ratio. A whole host of actuator springs (shown) can be tried and combined to achieve the perfect wastegate actuation threshold. Our goal with the Raw-Power turbos is to produce as much boost as possible while keeping drive pressure reasonable. With our primary objective being to avoid over-speeding the high-pressure turbo, we’ll start off with a lot of spring tension in the low-pressure turbo’s wastegate (the Precision unit) to make sure it’s not opening. On the other side of the coin, we’ll initially run a low spring tension in the high-pressure turbo’s wastegate (the Tial MV-R) as a starting point. We’ll progressively ramp up the spring tension, thereby allowing the turbo to see more and more pressure before the gate opens, until we see a boost-to-drive ratio we can live with. Then we can start dialing in the low-pressure turbo’s wastegate.
19 After bolting the top portion of our twopiece, 4-inch Street Diesel Performance downpipe to the low-pressure turbo outlet, the bottom portion was finagled into place. Because we decided to wastegate the low-pressure turbo (in addition to the highpressure charger), Elite incorporated an adapter into the downpipe to accommodate the secondary wastegate pipe.20 With the downpipe in place, the Precision wastegate for the low-pressure turbo was mounted to the driver side up-pipe, just below the exhaust manifold. With the cab back on the truck, this gate will be much harder to access for a simple spring swap. However, tuning this gate shouldn’t be nearly as involved as what it will take to dial in the high-pressure turbo wastegate on top of the engine.21 In this photo you can see how far the pipe used for the secondary wastegate spans. Overall, the wastegate system works like this: The high-pressure turbo vents drive pressure into the lowpressure charger in order to spin it harder (via the water-cooled Tial wastgate). However, in the event the low-pressure turbo sees excessive drive, exhaust will be routed to the Precision wastegate, through the underneath wastegate pipe, and directly into the downpipe.22 Back on top of the engine, the supplied one-piece stainless steel charge air pipe was installed. This piece is designed with ample room to clear the factory VGT actuator, which was reinstalled once the T-bolt clamps shown were cinched down to our liking.23 With the Raw-Power compounds all but installed, the supplied braided oil feed lines were connected. At this point, the only remaining items were to reinstall the engine harness, add an oil filter relocation kit, lower the cab (with all that entails), and install the hot-side intercooler pipe.24 Because we can always pull fuel out of the equation via PCM tuning, a set of River City Diesel 150% over nozzles were installed on a fresh set of injectors. With this kind of fuel on tap (150hp units can support well over 1,000 rwhp) the fact that we’re running dual wastegates (and a water-cooled high-pressure gate to boot) starts to make sense.25 To support the 150% over injectors, one of Elite Diesel’s Twin K16 high-pressure pump systems is being employed to maintain rail pressure. For extra insurance, we upsized to Elite’s Stage 2 fuel rails as well. The bored-out rails provide 25% more storage capacity than stock. A homemade, competition-ready low-pressure fuel supply system incorporating an Aeromotive A1000 feeds the K16s plenty of diesel.
With a built 6.4L Power Stroke sitting in our stable, we plan to see how fast Elite’s Raw-Power system can push a standard cab, four-wheel-drive ’08 F-250 through the traps. The engine was put together with R&R connecting rods, River City Diesel fly-cut and coated International pistons, Elite’s Stage 1X cam, Stage 2 valve springs, Stage 2 chromoly pushrods, H11 head studs, 150% over nozzles, and Twin K16s, so it’s ready for a steady diet of fuel and boost. We’ll tackle the install this month, followed by a trip to the chassis dyno and a fair amount of fine-tuning the wastegates and PCM after that. Stay tuned…DW
