Installing an S366 SX-E on an LBZ Duramax

Although the factory Garrett GT3788VA found on ’04.5-10 Duramax mills has proven to be one of the most reliable variable-geometry turbochargers in the diesel truck segment, nothing lasts forever—especially a VGT. When these turbos fail, a lot of GM owners begin to take stock of what the market around them offers for replacements, and many of them opt for an upgrade. Sure, you can clean the turbo or start over with a fresh unit, but what if you want to make more power one day? In most Duramax applications the stock turbo runs out of gas somewhere around the 530rwhp mark, and although that’s a decent number for a daily driver, the turbo is doing little more than moving hot air at that point, causing EGT to climb to alarming levels.

HSP Diesel has a reputation for offering some of the highest-quality Duramax components on the market, and the company’s S300 single-turbo installation kit did not fail to meet our high expectations. Very few tweaks were required to install everything, and the fit and finish is top-shelf. The system comes with everything you need to replace the factory GT3788VA on your LBZ Duramax, including a T4 pedestal, downpipe, intercooler pipes, a cold-air intake and any color of powdercoating you want. In this particular kit the raw piping has been clear-coated for an industrial yet glossy look.
The most time-consuming aspect of any turbo swap as it pertains to a Duramax revolves around the teardown process. With the hood of his ’07 Silverado up and in the service position, Garrett Oxley had roughly two hours invested in getting to this point.
With the factory VGT free at the back of the lifter valley, Oxley cocked the turbo upward and began to finagle it out from under the cowl. Be prepared to work in tight quarters and wrestle some very tight bolts if you attempt this job yourself.
Once the stock turbo was out of the way, Oxley got started with the installation of the S300. Because oil will top-feed into the S300’s center cartridge, the factory provision in the block is capped off via the supplied 12mm oil feed plug. HSP supplies a new oil feed line with its kit as well, which spans from the passenger side of the block to the turbo.
Installing a completely new turbo system on your Duramax is also an opportune time to access the injection pump. With 197,000 miles on the original CP3, Oxley proactively chose to install a new unit at this time. Its replacement would be a Sportsman pump from Exergy Performance.
To accommodate both the S300 and the factory up-pipes, HSP supplies this T4 pedestal with its kit. The pedestal positions the bottom of the S300 five inches above the lifter valley, which provides ample clearance for the upsized, 3-inch-diameter intercooler pipes. The pedestal also mounts the turbo closer to the front of the truck but not enough to crowd the Y-bridge, making future turbo swaps a cinch.
The T4 pedestal makes use of the mounting points for the factory turbo and HSP includes four pedestal studs and nuts with its S300 install kit. In this photo you can see how much higher the pedestal positions the new turbo, which makes intercooler pipe clearance around the engine’s nest of wire harnesses a non-issue.

After noticing a noise indicative of bearing failure, Garrett Oxley, an experienced diesel technician, used the occasion as an opportunity to upgrade his 197,000-mile ’07 Silverado 2500 HD. For ultimate reliability, he decided to scrap the VGT in favor of a fixed-geometry charger. And for a turbo that would drive well with stock injectors in the mix yet not be outmatched with a future nozzle upgrade, he opted for a BorgWarner S366 SX-E. To get the new turbo on the truck, Garrett reached out to HSP Diesel for one of the company’s S300 single-turbo installation kits. The comprehensive system would come with everything needed to perform the conversion, and the fit and finish of the HSP kit was second-to-none. Follow along for a full recap of the 8-hour install.

The forged milled compressor wheel in the S366 SX-E features a 66mm inducer, a 91mm exducer, and flows 90 lbs/min. A 360-degree thrust bearing comes standard on all SX-E turbos and adds durability to a charger that is easily capable of making more than 40 psi of boost.
A BorgWarner S366 SX-E may not be the S369 SX-E you’ve heard so much about (or the S372 SX-E that’s on the horizon), but the 66mm version moves just 140 cfm less than the 69mm wheel (1,285 cfm vs. 1,428 cfm). On top of that, the S366 SX-E spools much quicker. For Oxley’s stock-injector truck, this S300 was the perfect turbo for his daily driven and light towing needs. Like the rest of the SX-E line, the S366 SX-E features an integrated speed sensor port and a pre-machined boost port.
On the exhaust side the common 10-blade, 73/80mm turbine wheel is utilized. This specific turbo was fitted with the optional 1.0 A/R turbine housing, although a tighter 0.91 A/R housing is also available and comes standard. By opting for the larger A/R housing, some bottom-end response will be sacrificed to gain a little top-end flow.
Opening up airflow into the heads is HSP’s billet-aluminum, high-flow, 3-inch-diameter Y-bridge, which replaces the restrictive 2.5-inch, cast-aluminum factory piece. The bridge section is precision CNC machined for maximum efficiency and a perfect fit.
An optimized seal is paramount when elevated boost pressure is passing through the Y-bridge. This is precisely why two high-quality molded rubber gaskets are included with HSP’s Y-bridge.
HSP’s Y-bridge also includes a provision for the factory mass airflow sensor. Always take care not to damage this little guy while swapping it over, as an OEM replacement will run you nearly $500.
Each kit comes with a two-piece downpipe, which simplifies its installation. The upper section (shown) measures 3.5 inches in diameter, and the lower section measures 4 inches and works in conjunction with aftermarket (4-inch) exhaust systems.
HSP’s aluminized steel downpipe is ceramic coated to aid exhaust flow and spool-up, and Oxley treated his to a layer of heat wrap as well. The 3.5-inch upper downpipe section connects to the S366 SX-E via the supplied stainless steel V-band clamp.
With the downpipe loosely positioned on top of the truck’s existing exhaust system, the factory up-pipes were reinstalled. Oxley sourced a fresh set of exhaust manifold to up-pipe gaskets from Merchant Automotive, and also installed new up-pipe bolts while he was at it.
After a new T4 divided flange gasket had been placed over the studs in the pedestal, Oxley set the S366 SX-E on top of it. The fact that the HSP pedestal moves the turbocharger’s mounting location slightly forward makes fighting the cowl a thing of the past.
As you can see, the 3-inch Y-bridge definitely takes up more real estate in the valley, but even with the turbo’s mounting location being moved forward plenty of clearance exists between the two components and installation is fairly effortless. We’ll note that on LB7 engines the factory fuel return line has to be reworked in order to accommodate the larger Y-bridge.
Each HSP Y-bridge incorporates two 1/8-inch NPT ports, which can be used to read boost pressure or inject water-meth or nitrous. In Oxley’s application one will be used for boost reference, while the other port will be plugged with one of the two plugs provided by HSP.
Complementing the higher-flowing S366 SX-E charger and 3-inch Y-bridge, HSP’s 3-inch-diameter, mandrel-bent intercooler pipes flow 40 percent more air volume than the factory tubes. Here, Oxley routes the supplied hot-side pipe to the intercooler. Both intercooler pipes feature smooth, sweeping bends and straight connection points at the turbo and intercooler, which reduces the risk of blowing boots under big boost.
High-strength intercooler boots are composed of five layers of heat-resistant fibers and a high-temp silicone casing. In addition, the 3×4-inch straight intercooler boots included in HSP’s kit measure an inch longer than what comes in comparable kits. For a smooth transition from the S300 compressor outlet to the hot-side intercooler pipe, a 2.5×3-inch reducer boot is provided (shown).
Other miscellaneous items replaced during the install would be a new serpentine belt tensioner and an idler pulley. Again, like the CP3 replacement, it pays to perform any preventative maintenance measure you can afford when you’ve dug this far into the top of a higher-mileage Duramax.
Installing all of the intercooler piping was surprisingly easy for Oxley, which speaks to the great fit and finish of the entire HSP system. We’ve seen a lot of fitment issues in all our days being around aftermarket turbo systems, but very few surfaced during the installation of this kit. The well-engineered cold-air intake entails a heat deflection box, which with an air-tight seal keeps hot engine temps from entering the air filter. Additionally, and while it’s hardly visible here, Oxley did have to relocate the the transmission dipstick tube to the passenger side of the truck.
Swapping to a fixed-geometry turbo called for a tuning revision from In addition to disabling factory VGT parameters, the drive pressure reduction and higher boost levels provided by the S366 SX-E have to be built into the truck’s tuning files to optimize performance and drivability. Essentially, the truck’s computer has to be told that the engine’s boost curve will be different now, and that everything is OK.
A DSP5 switch allows Oxley to navigate his freshly tweaked Optimized Stock, Heavy Tow, Light Tow, Sport Economy and Race tunes from Spending most of his time in the Sport Economy tune, Oxley hardly noticed the expected reduction in low-rpm responsiveness the fixed-geometry turbo brought and thoroughly enjoys the hard mid-range and top-end hit the S366 SX-E provides.



HSP Diesel

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