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Installing Smeding Diesel’s S400 Kit On A Fourth-Gen 6.7L Cummins

Right out of the box, the 6.7L Cummins is a potent performer. But while its variable geometry Holset HE351VE provides instant throttle response, promotes huge off-idle torque, and offers a factory exhaust brake function, its track-record for long-term reliability isn’t exactly commendable. Oftentimes the VGT actuator stops functioning, but occasionally mechanical turbo failure transpires. When either of these problems occur, the owner is faced with a decision to either stick with the problematic VGT or start over with a proven, fixed geometry replacement. Thanks to the displacement increase the 6.7L enjoys over its 5.9L predecessor, a BorgWarner S400-based turbo can be run with no tangible sacrifice in drivability—even with a completely stock fuel system.

With the factory Holset VGT beginning to check out on our ’12 Ram 2500 test mule, the products offered by Smeding Diesel caught our eye. The Texas-based company has earned a reputation for developing high-quality, comprehensive turbo kits in recent years, and its pricing is on-point. We reached out for one of Smeding’s S400 turbo kits, its one-piece stainless-steel exhaust manifold, True-Flow intake horn, and the company’s grid heater delete. Following the install, and despite the truck still sporting the factory fuel system, it was immediately apparent that the newfound airflow had uncorked the engine’s true potential. If you’re on the fence about ditching the factory VGT, don’t be. Adding an S400 to a 6.7L Cummins is one of the best mods you can make to an ’07.5-current Ram. 

With its standard S400 system listed for $2,529 (with turbo), Smeding Diesel’s S400 Kit is definitely priced to sell. And even though we opted for the billet wheel S464 over the standard cast version, upgraded to its one-piece exhaust manifold, and tacked the company’s 360-degree thrust bearing, TrueFlow intake horn, and grid heater delete option onto our bill, we still got out the door for less than $3,500. For the sake of comparison, a remanufactured factory Holset VGT for a ’12 Cummins retails for roughly $2,200.
The contents of Smeding Diesel’s standard ’07.5-’12 6.7L Cummins S400 Kit looks like this. Everything required to replace the factory VGT comes in the box, which includes a 4-inch downpipe, three-piece exhaust manifold (not shown) and new gaskets, hot-side intercooler pipe and boots, a 90-degree cast compressor outlet, a 5-inch air intake system, and all necessary oil lines, coolant plugs, hardware, and clamps.
Smeding builds, tests, and validates all of its turbochargers in-house, and its T4 S400 line ranges from 64mm all the way up to 72mm for its ’07.5-’12 S400 Kit. In our case, because we were working with a stock fuel truck we went with the smaller S464, but elected to run the company’s billet compressor over the standard cast wheel. The billet 64/83/1.0 we chose retails for $1,049—not bad for a billet wheel S400. Taking advantage of the company’s 360-degree thrust bearing option, we also upgraded the turbo for utmost durability.
Smeding’s one-piece exhaust manifold is a solid, quality piece of hardware. Made of 316 stainless steel, the second-gen style manifold is highly resistant to corrosion and high temperatures, and also works with all 24-valve Cummins cylinder heads from ’98.5-present. The major benefit of the second-gen style manifold is that, by perfectly centering the foot (rather than having a rear cylinder bias, like stock) an equal amount of exhaust gases flow to the turbine.
The proven 74/83mm turbine wheel sits on the other end of our S400’s shaft, and it’s a turbine that works well in applications ranging from 500 hp to 800 hp. In conjunction with a relatively tight 1.00 A/R exhaust housing, low-end drivability will be adequate but at the same time high rpm exhaust flow won’t be restricted due to excessive drive pressure. One of the key reasons behind an S400’s immense horsepower gains over the stock VGT (other than size) lies in the drop in drive pressure it provides.
Whether you’ve been around 6.7L Cummins S400 installs in the past or not, it’s worth noting that you save yourself a lot of work by splitting the turbo and making the exhaust manifold and exhaust housing a single assembly rather than installing the manifold and complete turbo separately. After setting the supplied T4 turbine inlet gasket in place on the manifold, that’s exactly what we did (shown).
The billet compressor wheel in our S400 features six blades and measures 64mm at the inducer. Developed over the course of several years, it’s a lightweight, high-flow design that provides a noticeable difference throughout the rpm range when compared to a conventional BorgWarner cast wheel.
With the factory VGT eliminated, there is no longer a need for engine coolant to flow to the turbo’s center section (just oil with the S400). Smeding includes the shallow water block-off plug caps to accomplish this and the one we installed in the coolant port in the block near the oil filter is shown here. In case you’re wondering, for adequate access to the block we pulled the truck’s passenger side inner fender liner for the duration of the turbo system install.
When it was time to install the exhaust manifold (which again was already fitted with the turbo’s exhaust housing), two manifold bolts were threaded approximately halfway into the head. Then with the manifold loosely in place, all of the other bolts were installed, along with new manifold gaskets. After that, we went back to the original two bolts, removed them, inserted gaskets, and installed the bolts for good.
To make the installation of one of its exhaust manifolds as seamless and event-free as possible, Smeding Diesel sells an exhaust manifold bolt kit (which we used). For us, the minimal $36 is cheap peace of mind for anyone installing a new manifold. The exhaust manifold bolt kit includes M10 Allen head bolts and washers.
Smeding supplied a -10 oil drain flange for the S464 and for added insurance we ran a bead of Permatex’s The Right Stuff for optimum sealing. Then the oil drain flange was installed on the turbo’s center section using the included washers and Allen bolts.
Once the oil drain was in place, the rest of the turbo assembly could be installed (the center section, exhaust wheel, compressor housing, and compressor wheel all as one unit). Things were definitely tight with the exhaust manifold, oil filter base, and battery tray all being in such close proximity, but once it was installed ample clearance was available between everything. We’ll note that we also positioned all clamps so that they could be loosed (or tightened) easily from up on top of the turbo.
Next up, we installed the supplied oil drain line that spans from the turbo’s center section to the block. Then the included oil supply line was attached to the top of the turbo’s center section. The oil supply line pulls oil from the engine’s oil cooler cover.
Proper routing of the hot-side intercooler pipe was made possible with this cast-aluminum, 90-degree elbow from Smeding Diesel (also called an “S400 transfer elbow”). The elbow, which seals via O-ring, connects to the compressor housing outlet with a supplied V-band clamp. The lip on the discharge side of the elbow is there to ensure its respective intercooler boot doesn’t blow off under boost.
Linking the compressor outlet to the intercooler is this aluminum hot-side pipe. Quality, straight-fit silicone boots that resist heat, boost pressure, and oil are supplied for each end of the hot-pipe. And, just like the 90-degree elbow it connects to, both ends of the hot-pipe feature a bead to keep boots from blowing off. The hot-side pipe installs via stainless steel T-bolt clamps.
Thanks to 5-inch diameter piping, there is certainly no restriction on the air intake side of the equation. Installing Smeding’s 5-inch diameter air intake system starts with the supplied 45-degree rubber boot, which fits over the compressor inlet. Note that on some fourth-gen Rams you may have to relocate the grid heater relay forward in order to clear an intake this big.
Smeding’s polished 5-inch intake tube integrates both the factory mass air flow (MAF) and intake air temperature (IAT) sensors. After swapping the sensors over, the intake tube was finagled into the previously-installed 45-degree rubber coupler.
The final touch on the air intake assembly was the S&B filter supplied in the S400 Kit. Its wet (oiled) design means it’s cleanable and reusable, and its sizable dimensions mean it should be able to flow plenty of air for the S464 to compress. Installing the worm gear clamps (supplied in Smeding’s kit but not yet in place) were the final step in securing the air intake system in place.
Turning our attention to the grid heater delete, we decided to pull the valve cover in order to make removal of the factory one easier. With the valve cover out of the way, we knew the job of pulling the fuel rail (which has to be removed first) would be much easier, too.
When we pulled the fuel rail, we took special care that no debris entered its ports. Then the bolts that hold the factory grid heater plate to the head were broken free via 10mm socket and the plate was removed. From there, we carefully removed the remaining grid heater plate gasket material from the mating surface on the head.
As you can see, without the grid heater in the mix, a whole lot more airflow makes it into the head. Smeding Diesel’s billet intake grid heater delete plate is made from 6061 aluminum, accepts the factory EGT thermocouple (which we swapped over), and ships with four spacers to properly remount the fuel rail.
In addition to offering vastly improved air flow into the head, the Smeding grid heater delete plate eliminates a failure point that’s becoming more and more prevalent as common-rail 5.9L and 6.7L’s continue to age. This stud and nut on the underside of the factory grid heater is prone to deteriorating with vibration, heat, and age and can break off, fall into the intake runner and head, and even make its way into the number 6 cylinder, where it can cause all kinds of mayhem.
Smeding’s TrueFlow intake horn matches its grid heater delete plate perfectly, completing the restriction-free path for air to enter the engine. The intake horn is cast from aluminum for exceptional cooling properties and strength, and features multiple 1/8-inch NPT ports integrated in the backside of it for measuring boost or adding injectables. It accommodates the factory manifold absolute pressure (MAP) sensor as well.
The last order of business was installing the supplied 4-inch downpipe, and it was here that we were most thankful we’d decided to install Smeding’s S400 system with the truck on a two-post lift. We manipulated the downpipe into place with the truck’s existing 5-inch exhaust system with help from a new 5x4x6-inch Donaldson reducer.
By early afternoon, we’d successfully pulled off the install—and in the process laid the groundwork for fueling mods, which we plan to perform in the future (to the tune of 30 or 60-percent over nozzles and a 10mm CP3). During the initial testdrive following the install, our immediate feeling was that we’d picked up at least 50 hp over the factory VGT. The day after the install was Sunday, which meant fishing. Hooked to 7,000 pounds worth of boat and trailer, the truck felt exceptionally responsive down low for being equipped with an S400. And no surprise to us, it pulled much stronger in the midrange and especially at higher rpm.

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