DURAMAX VVT SCIENCE
AN INSIDE LOOK AT THE HT TURBO PROMAX 64
BY J.S. HANSEN
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.
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 backpressure and EGTs for daily driving and towing applications. It also bolts directly in place of the stock unit, with no other changes necessary.
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 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.