Diesel Tuner's Blog

How VVT/VGT Turbochargers Work on Your Diesel

Posted by Paul Wilson on Jul 24, 2021 9:30:00 AM

Turbocharging diesel engines is nothing new.  The most basic premise of a diesel engine is the more fuel and air you mix during compression, the more power you get. 

Types of turbocharger systems:
  • Wastegate Turbocharger
  • Fixed Vane Turbocharger
  • VVT/VGT Turbocharger
  • Compound Turbocharger 
  • Twin Turbocharger
  • Dual Scroll Turbocharger


Between 1885 and 1916 a few patent applications were submitted for products that address the general concept of turbocharging, but it was in 1925 that Swiss Engineer Alfred Buchi put the first commercially available turbo on a 10 cylinder diesel engine.  Turbochargers use exhaust gas pressure to drive a Turbine Wheel that is connected to a Compressor Wheel. The compressor wheel forces cold air into your engine. You're using exhaust pressure to create boost pressure. 

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As OEM technology has advanced over the last century, peak horsepower and torque offerings have too.  Right now in 2021, Ford, Ram, and GM all offer diesel trucks with around 1,000 ft.lbs of torque right off the showroom floor.  All 3 also come with advanced emissions systems, automatic transmissions, high-pressure common-rail fuel injection, and a VVT/VGT Turbocharger. 

VVT: Variable Vane Turbocharger

VGT: Variable Geometry Turbocharger

6.0L Stealth 67 Unison Ring, vane, exhaust housing (1)

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Diesel performance technology at an OEM level seems to be driven by 3 factors.

  1. Consumer demands for more power and performance
  2. Emissions Standards set by federal and state authorities (EPA & CARB)
  3. Increasing reliability (Warranty claims cost $)

We can't be positive if the Torque Wars that have been taking place for the last 2 decades is a very public pissing match between manufacturers or if consumers really need the dramatically increasing amount of power available in stock diesel trucks. Either way, diesel performance enthusiasts like us are the clear winners.  

A part of the reason these huge power numbers are possible (while meeting emissions and reliability standards) is the leaps and bounds that have been made in turbocharger technology.  As previously stated, 6.7L Cummins, 6.7L Power Stroke, and 6.6L Duramax offered in 2021 include a Variable Vane/Variable Geometry Turbo.  

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How VVT/VGT's Work!

As exhaust enters the backside of a turbo in the turbine housing, it pushes your Turbine Wheel.  For years guys have played around with how much space should exist between the turbine wheel and turbine housing.  Generally, this relationship is expressed in an Aspect Ratio (Aspect Ratio (AR) is the ratio of the area of the exhaust turbine inlet to the radius from the turbine impeller center).  What you really need to know is less space between the turbine wheel and turbine housing results in less time and energy that it takes for the wheel to start moving.  This directly impacts spool-up and the turbo's ability to manage Drive:Boost Pressure Ratios.  

Exhaust Housing

A Variable Vane Turbo uses "Vanes" to channel the exhaust coming into the turbine housing around the turbine wheel more precisely.  Think of it like when you put your thumb partially over a garden hose to spray water. There's a relationship between how much of the hose you cover and how hard the water sprays out.  VVT technology works the same way.  The vanes are able to be moved and angled in different ways to change how the exhaust flows around the turbine wheel.  When the vanes are "squeezed" the exhaust pressure being applied to the turbine wheel is increased.  This function widens the turbo's efficient operating range.  

VVT/VGT's ability to dynamically change Aspect Ratio results in a turbo that can spool up quickly, adjust to any driving conditions, and maximize MPGs.  When you're towing up a steep grade through the mountains your truck has the proper sensors to detect elements of that situation and operate the turbo in a manner that keeps your truck as safe as possible while getting the best performance out of it. 

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Topics: Turbo, LB7 Turbo, LBZ Turbo, LML Turbo, Diesel Turbo Options Duramax, Duramax Turbo, LLY Turbo, VGT, VVT