DURAMAX VVT SCIENCE

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 backpressure in the exhaust stream to force exhaust gases through the Exhaust Gas Recirculation (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 500hp 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 400-600hp crowd.

First off, on the compressor side of the LLY and LBZ turbochargers, the stock 11-blade wheel is replaced with a 63mm billet 6-blade wheel that will increase volume at similar boost pressures. This wheel design offers better flow and engine efficiency in the midrange 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 profile wheel, which will better handle the exhaust flow being created within the engine at the higher horsepower levels. The change to a

 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 500hp applications. For those looking to reduce EGTS and backpressure at higher power...

 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...

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

 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 over 600 hp.

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