VGT Turbo Exhaust Brake Fail! And how you can prevent it. With the ability to vary the flow of exhaust gasses across the turbine wheel, variable geometry turbochargers (VGT’s) get us as close as possible to having the best of both worlds. At low rpm, restriction in the exhaust side (i.e. drive side) of the turbo is increased, effectively making the Why VGT act like a much smaller turbo. At high rpm, all restriction is removed and you get the impression that a much larger turbo is feeding the engine.