The introduction of the Variable Vane Turbocharger (VVT) on the LLY GM Duramax in 2004 may have been mostly emissions-control related, but in the years since, it has proven to be a solid performer with great power potential—with a few tweaks from the aftermarket. The Garrett VVT used on the 2004.5-2016 Duramax has gone through a few revisions with each engine platform, but it remains a pretty solid turbocharger for daily driving, towing, and power output up to around 530 horsepower.


Ready for assembly, this LBZ Duramax Variable Vane Turbo has already been inspected, cleaned, machined, and balanced. Modifying the stock unit to the ProMax 64 specifications includes a larger billet compressor wheel and high-flow turbine wheel to increase flow, reduce backpressure, and lower EGT.


The factory LLY compressor wheel was the largest for the 2004.5-2016 trucks at just under 63mm. The 12-blade design offers good lowrpm response, but lacks high-rpm flow.

But as with anything else, the aftermarket always finds ways to improve performance, and the VVT turbo is no different. High Tech Turbo of Salt Lake City has specialized in everything turbo since 1985 and has been modifying the OEM Duramax turbochargers for quite a few years with great success. The ProMax 64 will support up to 600 rear-wheel horsepower and can reduce exhaust back-pressure and EGTs for daily driving and towing applications. It also bolts directly in place of the stock unit, with no other changes necessary.


For the following models, starting with the LBZ, GM went to a smaller compressor wheel size. The 60 mm wheel is still more than enough to support a 500 hp truck.


The HT Turbo ProMax uses a unique 63 mm 6-blade billet compressor wheel with staggered fin heights to improve overall airflow through the entire rpm range. The change in wheel design increases volume, meaning better engine efficiency with better peak power and EGT control.

When GM started looking for ways to reduce emissions in the 6.6L Duramax engine, the variable geometry turbocharger helped immensely. By allowing quick low-rpm response, the VVT can better control smoke output at low boost, all while creating higher back-pressure in the exhaust stream to force exhaust gases through the Exhaust Gas Re-circulation (EGR) system. Keeping the exhaust vanes closed makes it feel like a small turbocharger with good response. But opening those vanes up so the exhaust can flow freely gives it the feel of a larger turbocharger for better power and temperature control, to a certain point at least. Running low 500 hp tunes, most owners will see extreme EGTs and excessive drive pressure numbers at wide open throttle. The compressor wheel just won’t move enough air and the restrictive turbine side becomes a choke point and limitation to safely making more power. To overcome this, HT Turbo upgrades both the compressor and turbine wheel with larger, high-flowing wheels that are better suited for the 400-600 hp crowd.


On the turbine side of the Garrett VVT, the factory 12-blade exhaust wheel (left) offered a good balance between spool-up and power, again best suited for up to 500 hp applications. For those looking to reduce EGTs and back-pressure at higher power levels, the ProMax turbocharger uses a larger exhaust wheel with 10 blades.


Converting to the 10-blade turbine wheel will move more exhaust more efficiently, thereby reducing drive pressure. While slightly larger than stock, this turbine wheel offers great spool-up and will support up over 600 hp.


These vanes show one of the other differences between LLY and LBZ turbochargers. The shorter vanes belong to the LBZ, which helped low-end performance with the six-speed Allison.

On the compressor side of the LLY and LBZ turbochargers, the stock 11-blade wheel is replaced with a 63 mm billet 6-blade wheel that will increase volume at similar boost pressures. This wheel design offers better flow and engine efficiency in the mid-range for better power and EGT control. Of course, the compressor covers are machined to accept the larger compressor wheel. On the exhaust side, the factory 12-blade turbine wheels are replaced with a 10-blade pro wheel, which will better handle the exhaust flow being created within the engine at the higher horsepower levels. The change to a larger-diameter 10-blade wheel will reduce drive pressure without affecting spool-up. In most cases, a minor tuning adjustment within the vane control tables can make this turbocharger drive almost like stock, until you hammer on it and really feel that broader torque curve from the major jump in air flow.


HT Turbo also upgrades to a 360-degree thrust bearing (bottom) to better handle the extra load and stress from running higher boost and power levels.


Every turbocharger has the rotating assembly balanced to ensure longevity and reliability of the unit. Spinning at over 120,000 rpm, the slightest imbalance can create premature wear and failure.

Along with their custom machining and wheel upgrades, HT Turbo also upgrades some of the internal pieces, such as changing to a 360-degree thrust bearing to better handle the stress and added load the turbo may see at higher boost levels. Each charger is cleaned, inspected and closely measured to ensure the new bearings and seals will be within OEM specifications. The rotating assemblies are also fully balanced on high speed balancers so that premature bearing failure can be avoided.


The Heins Balance machine is used by many turbocharger companies and offers great reliable balancing results. By pinpointing the heaviest point of the wheel, it can then be machined to remove weight until it balances within spec.


The oil plunger is one of the first pieces installed into the bearing housing. This plunger will move back and forth within the bore, which moves an internal gear that will control vane position.


The notched plunger must be lined up with the teeth of the vane gear to ensure the vanes unison ring will rotate properly to control vane position while driving.


Each bearing housing is inspected for any flaws and has the bearing
bores measured to make sure the proper bearing tolerances are


The thrust collar is installed into the bearing housing, followed by the new 360-thrust bearing. There will then be a square O-ring installed to seal the bearing housing to the aluminum back plate, which is next to go on.

If there is one common flaw within the Garrett VVT design, sticking vanes or a failed unison ring, which controls the exhaust vanes, is the most likely culprit if you experience intermittent response and driving issues from the OEM VVT unit. On high-mileage trucks that have seen a lot of soot and exhaust build-up over time, any small moving part, like those vanes, could see some wear. Unfortunately, these issues are just the nature of the beast within any variable geometry turbo. Of course, all these pieces are fully cleaned and inspected before assembly of a new ProMax 64 to be sure everything will work as it should once installed on a customer’s truck.


The back plate receives a new compressor side thrust collar and piston ring to ensure oil doesn’t weep past the collar.


With the bearing housing turned over, the new journal bearings and the bearing spacer can be dropped into the bore.

Speaking with Braydon Price of Meridian, Idaho, who recently installed the ProMax 64 on his mildly built LBZ truck, we were able to get firsthand feedback on his modified VVT. He had been looking to improve peak horsepower in his Max Effort tunes, while reducing EGT towing in his lower horsepower tunes. Price works as a sales rep at Adrenaline Truck Performance (ATP Trucks), so he knows a bit about these trucks and what it takes to really dial one in. With a cold-air intake, 4-inch exhaust, lift pump, and a built Allison transmission, the truck made 512 hp in his Max Effort tune with the stock turbocharger. Swapping over to the High Tech Turbo ProMax 64, the peak output jumped to 574 hp, an increase of 62 horses with no other changes to the truck. Best of all, the pyrometer gauge has shown drops of nearly 150 degrees at wide open throttle, and he’s also reported it being much easier to control EGTs while towing heavy in tunes that make 400 hp.


Before inserting the turbine shaft into the bearing housing, a new piston ring is installed; this seals oil inside of the turbo.


With the turbine wheel and shaft installed, the new billet compressor wheel can be installed and will be torqued to spec. While the factory compressor wheels have the threaded nut as part of the wheel, HT Turbo opts to use a separate nut from the wheel. This allows the wheel to be lined up more precisely on the predetermined balance marks.

The crew at High Tech have seen trucks running mild injector upgrades and healthy CP3s make more than 600 hp with this turbo with near stock driving characteristics. The ProMax 64 is currently available for the LLY and LBZ platforms, but a direct bolt-in upgrade is nearing release for the LMM and LML trucks as well. For those of you looking to maintain all the factory emissions equipment (DPF, Urea, EGR), the aftermarket is catching up, and any of these turbos should be a great upgrade for improving airflow to that big Duramax engine, regardless of the model year.


With the rotating assembly complete, the oil control solenoid is then installed, but not before all new O-rings are installed. Controlling oil pressure and eliminating internal cross leakage here means better vane performance.


The turbine housing needs to be loaded up with vanes before the turbocharger assembly can be completed.


The unison ring in this position shows the vanes fully closed to restrict exhaust flow, aiding in the low-end response of the turbo for quick spool-up.


As exhaust flow increases, the vanes can be opened to allow that exhaust to escape, giving better performance at hard throttle.


Each vane is slipped over the posts in the exhaust housing, then the unison ring is installed, which ties the vanes together as one. The unison ring is controlled by the gear-driven post on the exhaust side of the bearing housing.


The completed ProMax 64 is now ready for installation on a customer’s truck. Dyno testing on a 2006 LBZ with a built transmission, lift pump, intake, and 4-inch exhaust has shown 70+ horsepower at the rear wheels while reducing EGTs by more than 150 degrees.