Subscribe to the Free
Newsletter
  • |
  • |
  • |
  • Compound Turbos Bring New Life to a 5.9L Cummins Engine

Compound Turbos Bring New Life to a 5.9L Cummins Engine

Under Pressure

Bruce W. Smith
Mar 13, 2018
Photographers: Bruce W. Smith
Hopefully, you’re familiar with the “Big-Three Blend” series of Diesel Power tech reports in which we detail all the tasks for transplanting a mildy warmed-up 24-valve 5.9L Cummins engine and Allison 1000 six-speed automatic transmission into an ’01 Ford F-250. The result of that effort is a fun daily driver. However, as it is for most diesel projects, the taste of driving something out of the ordinary—like a “Fummins” (the diesel guys’ name for a Cummins-powered Ford rig)—only whets one’s appetite to take it to the next performance level.
In our case, that means moving up from a big single turbocharger to a compound-turbo system. The reasons for doing this are to reduce the high EGT we experience when towing a trailer heavier than 7,500 pounds, to quicken low-end spooling, and to push the I-6 engine as close to 500 hp as we can with its Cummins-based fuel supply (VP44 injection pump).
Our “stock” setup features a BD Diesel Performance exhaust manifold, Industrial Injection Diesel Performance’s PhatShaft 62mm turbo and Race2 Honed X4 120hp injectors, Fuelab’s 200-gph lift pump, the aforementioned VP44, Banks Power High-Ram intake, and an Edge Products Juice with Attitude programmer managing the electronics. We took it to Source Automotive in Clackamas, Oregon, where Robert Gates ran it on a Mustang chassis dyno to record baseline data. The truck made a respectable 316 hp at 2,700 rpm and 681 lb-ft of torque.
Photo 2/27   |   Compound Turbos Install

What Is Compound Turbocharging?

In a nutshell, compounding involves using a second, larger turbocharger to blow into a smaller turbo. The larger primary “atmospheric” turbo of a compound setup sucks in the fresh air, compresses it, then force-feeds boost through piping directly into the smaller, secondary “high-pressure” turbo mounted on the exhaust manifold. At the same time, the smaller high-pressure turbo feeds exhaust directly to the larger atmospheric turbo, helping it spool quicker.
Reducing each turbo’s workload increases efficiency while dramatically increasing boost pressure. At the same time, EGT can be more than 200 degrees cooler under full load because the resulting air/fuel charge is denser, cooler, and of far greater volume than can be achieved with a single turbo.
Another big advantage of compounds over single turbos is keeping exhaust and boost pressures nearly equal. For example, in a single-turbo application, the exhaust pressure may be at 65 psi before entering the turbo, while boost pressure at the intake might only be 35 psi. A set of nicely matched compounds sees the same exhaust pressure, but boost is closer to 63 to 65 psi, or that ideal 1:1 ratio.
A person can get deep in the weeds discussing compound turbos and all the numbers that go into selecting the right combination for whatever a goal is. (For all you “numbers people,” when it comes to turbo selection, check out BorgWarner’s “Match-Bot” page: turbos.bwauto.com/aftermarket/matchbot.aspx.)
Photo 3/27   |   Here is BD Diesel Performance’s street/tow compound-turbocharger kit for the Cummins 24-valve 5.9L engine, mounted in our ’01 Ford F-250 with custom plumbing by GOS Performance. We also used BD’s three-piece, 23-degree, pulse-flow exhaust manifold to keep the turbos close to the block.
Let’s just say it’s a science best left to diesel-performance experts who deal with turbos day in and day out. They know what the pressure maps are for every ’charger they sell, how the size of the inlets and outlets for the compressors and turbines match up, what each turbo’s A/R (Area/Radius) is, which injectors and fuel pumps work best, and how all those combinations work for a particular engine.
“You have to be clear on your goals when selecting compounds,” says Dan Kizmann, Lead Technical Support at BD Diesel Performance. “If you are towing heavily on a regular basis, the turbos we combine are considerably different than turbos used on a street/strip truck. Compound turbos must be sized perfectly for each application so they complement each other instead of working against each other.”
For example, Dan says a small, high-pressure turbo with a low A/R mated to an atmospheric turbo with a high A/R will never spool high enough to get to the sweet spot on the efficiency map of the system because the exhaust gas from the smaller turbo will not provide enough drive energy to the turbine wheel on the primary (atmospheric) turbo.
“Let’s say you went with a 366 over a 480, or a combination sized along those lines. What you’d experience is a lot of lag in the bottom end, and the engine wouldn’t reach its power potential on the top. It would be a terrible setup for towing. You want two turbos that overlap and complement each other for a specific application,” Dan says.
For diesels like ours, daily drivers that tow on a regular basis, compound-turbo experts recommend the high-pressure turbo should flow roughly 50 to 60 percent of the larger primary turbo’s flow capacity in pounds per minute.
To that end, BD’s turbo engineering specialists paired a BorgWarner S358 (.80 A/R) with an S472SX-E (1.25 A/R) for our VP44-fueled 5.9L Cummins. This new compound-turbo tow package (PN 1045420; $4,629) is a build-on-demand kit to precisely match each buyer’s needs.
Our S358 features a forged-milled billet 58mm compressor wheel and 64.5mm turbine wheel, while the primary S472SX-E spins a 72mm billet inducer and an 87mm exducer.
“Individually, the S358X flows about 57 pounds per minute, while the S472SX-E moves about 110 pounds per minute. When used in a compound system, these airflow ratings change because of the maximum volume limitation of the smaller secondary turbo,” Dan says. “But that air charge is considerably denser (richer in oxygen) thanks to the compression of the primary turbo.”
To further match the two, BD set the high-pressure turbo’s wastegate to open at 45 psi for quicker low-rpm response while protecting over-speed failure on the top end. That setting would also provide strong pulling power in the mid to upper rpm, as the non-wastegated S472 overlaps where the secondary turbo pops off.
Photo 4/27   |   Mobile Diesel’s Mat Johnson clears out the old single-turbo setup from our project-truck’s engine bay to make room for a BorgWarner S358/ S472SX-E compound-turbo package.
Using the correct turbos, injectors, injection pump, intake, and exhaust are all well and good—as long as the engine makes the right music when it’s all brought together. We reached out to Ben Brown at Accelerated Diesel Repair in Rapid City, South Dakota, for tuning help. He composes tunes for Cummins engines and uses MM3 Power’s programmer with accompanying touchscreen display and connecting hardware to flash calibrations into the ECM. The tunes are also compatible with Edge Products’ Competition Juice with Attitude programmer.
The Juice with Attitude taps directly into a stock VP44’s signal wire, which allows fine-tuning of the fuel metering and timing control solenoids, which the device also manipulates, potentially adding up to 120 hp and 380 lb-ft of torque according to Edge.
Ben spent hours developing the base tunes remotely, while Mobile Diesel’s Mat Johnson drove the truck and loaded the software updates into the ECM via the MM3 controller. Ben’s custom-tuning map includes additions and adjustments to the factory timing, injector pulse width, rpm, and fuel pressure. That enhanced “base” tune can then be paired with Edge’s seven levels of “competition” programming to make as much power as possible with our new setup.
A word of caution here: If you plan on pushing boost beyond 40 psi, which is something compound turbos will definitely do, use ARP cylinder-head studs and O-ring the head. “If that’s not done,” warns Source Automotive’s manager Bill Allen, “the head is going to lift—or worse. Guaranteed.”
Robert put our F-250 back on the dyno to see what the final numbers are with all the changes. The resulting 506 hp and 864 lb-ft made us smile. But what makes us even happier is the fact that EGT will probably never get anywhere near concerning levels when towing heavy loads.
Photo 5/27   |   The first task is removing and then drilling and tapping the oil cooler housing (installed when we swapped the Cummins into the F-250 in 2017) to facilitate adding two ¼-inch pipe fittings for the compound turbo’s feed lines. A 7/16-inch hole is drilled into the galley for the upper fitting, 1 inch from the center of the stock fitting.
Photo 6/27   |   We also removed a lower freeze plug on the passenger side of the engine. The hole is used for the turbo’s oil-return line after the compounds are installed.
Photo 7/27   |   Installing compound turbos requires placing the primary (atmospheric) turbo in first. The S472SX-E is a tight fit and requires a second person underneath to help mount it to the high-pressure turbo that sits above it.
Photo 8/27   |   To keep airflow maximized, we’re using BD’s X-Flow Intake. It has a smooth flow and pre-tapped ports for boost-gauge fittings. Many of the parts are powdercoated (by Double R Powder Coating in Sutherlin, Oregon) to add some color under the hood.
Photo 9/27   |   A must for this installation is using the 23-degree exhaust manifold, which keeps the turbos as close to the block as possible. This BD Pulse Flow version has better exhaust flow and uses a three-piece design that doesn’t crack over time from the constant heat expansion and contraction.
Photo 10/27   |   The BorgWarner SX358 is fitted with an ultra-light 7/7 FMW compressor wheel and is capable of grabbing a ton of air while keeping the airflow smooth. The billet wheel is also strong enough to endure the stresses of centrifugal forces created by speeds as high as 250,000 rpm.
Photo 11/27   |   The actual installation of the turbos is relatively easy. Setting the secondary “high-pressure” S358 in place and bolting it to the new intake only takes a couple of minutes.
Photo 12/27   |   Connecting the two turbos requires removing the truck’s inner fender and having a buddy crawl underneath to lift up the bulky S472SX-E so it can be bolted to the smaller high-pressure ’charger. Working space at this point of the installation is at a premium.
Photo 13/27   |   Here’s the main reason why the 23-degree exhaust is used. Notice how close to the 472 the Cummins block sits. When positioned correctly, there should be about a ½ inch of space between the lower turbo and the block. The downside of such a close fit is that it requires the pyrometer probes to be relocated to the top of the exhaust manifold instead of utilizing the pre-tapped ports underneath.
Photo 14/27   |   After we install both turbos, the S358’s compressor housing is rotated 180 degrees counter-clockwise to align with the charge-air cooler. We built our own plumbing for the cooler and air intake.
Photo 15/27   |   GOS Performance’s air-feed tube connects the primary and secondary turbos and creates a smooth path for the compressed air to flow.
Photo 16/27   |   Routing the oil feed and return lines takes a little time, as the oil cooler has to be reinstalled and the new fittings angled just right to fit the space. Note how we have the 45-degree cooler fittings angled and hoses routed.
Photo 17/27   |   Custom installations often require a little creative fabrication, which some gearheads call “MacGyvering.” Mat Johnson made the air-to-air intercooler tubes by cutting off the turbo end of the stock Ford pipe and welding together scrap pieces that have correct bends and a 2.75-inch inside diameter to fit the S358. Having a lot of odds and ends lying around a diesel shop really pays off when undertaking this type of project.
Photo 18/27   |   Plumbing eats up a lot of time, because it requires making project-specific parts.
Photo 19/27   |   You will be hard-pressed to cram anything else under our ’01 Super Duty’s hood. The BD Diesel Performance compound turbos fit like a skin-tight glove. But the performance gains are worth the effort in both time and expense for a daily driven work/play truck.
Photo 20/27   |   With space being so tight, we needed to find a way to keep turbo heat away from the air conditioning and other items under the hood. BD’s cool turbo covers handle that task with class and simplicity.
Photo 21/27   |   The easiest part of the compound-turbo upgrade is installing a Diamond Eye Performance 5-inch Super Duty exhaust. It slides into place without any modifications and sounds just as sweet as it looks.
Photo 22/27   |   This power graph illustrates how our compound turbos work with the 24-valve Cummins engine. The center gray shaded line (Total Boost) replicates a dyno run. The S358 (high-pressure) carries most of the load in the bottom end of the rpm range and starts to share its overall load once the S472SX-E (atmospheric) is spooled, at which point the two cross over and work together.
Photo 23/27   |   Edge Products’ Competition Juice with Attitude programmer taps into the stock VP44 injection pump’s signal wire and can potentially double the horsepower capacity for a stock pump. Don’t tap the WRONG wire as is shown here. It’s a common mistake. Tap the circled wire.
Photo 24/27   |   The compound-turbocharged 24-valve’s performance is enhanced by Ben’s remapping of the Cummins ECM. The “Brown Tune” changes timing, rpm, fueling, and pressure values, and is downloaded into the ECM through the MM3 Power programmer.
Photo 25/27   |   Bill Gates, Source Automotive’s lead dyno technician, put our rig through its paces on a Mustang 1750 dual-eddy dyno. The numbers jumped from 316 hp and 681 lb-ft to 506 hp and 864 lb-ft with the compounds and custom tuning.
Photo 26/27   |   We thought ARP cylinder-head studs would be all our original build with a single turbo would need. Adding compounds quickly showed us we should have also O-ringed the head when the engine was built. We learned an expensive lesson here.
Photo 27/27   |   GOS Performance’s Aden McDonell remotely adjusted the Allison 1000 six-speed automatic transmission’s shift strategy while the truck was strapped to the dyno. Aden’s tuning further enhanced how our truck runs with the compounds.

Sources

Edge Products
Ogden, UT 84404
877-760-5386
www.edgeproducts.com
BD Diesel Performance
Sumas, WA 98295
800-887-5030
www.dieselperformance.com
Source Automotive
Clackmas, OR 97015
503-654-9004
www.sourceautomotive.biz
Diamond Eye Performance
Athena, OR 97813
800-635-9950
www.diamondeyeperformance.com
Mobile Diesel Service
541-459-8939
mobilediesel.co
Double R Powder Coating & Fabrication
541-459-5662
www.facebook.com/Double-R-Powder-Coating-Fabrication
GOS Performance
800-620-4467
www.gosperformance.com
Accelerated Diesel Repair
605-391-4797
accelerateddieselservice.com
MM3 Power
208-346-7707
mm3power.com

POPULAR TRUCKS

MOST POPULAR

Subscribe Today and Save up to 83%!

Subscribe Truck Trend Magazine

Subscribe to:

Truck Trend
Magazine

PRINT DIGITAL
Subscribe Diesel Power Magazine

Subscribe to:

Diesel Power
Magazine

PRINT DIGITAL
Subscribe Truckin Magazine

Subscribe to:

Truckin
Magazine

PRINT DIGITAL
SUBSCRIBE TO A MAGAZINE
CLOSE X
BUYER'S GUIDE
SEE THE ALL NEW
NEWS, REVIEWS & SPECS