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Old 12-11-2013, 05:48 PM
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Hario' Hario' is offline
SuperTurboDiesel
 
Join Date: Dec 2013
Location: London, UK
Posts: 17
The issue with boost referenced actuator controlled VNT is when you lift off after boosting and the manifold pressure drops is the actuator slams the vanes back to closed position and causes a massive exhaust braking effect.
VNT vanes in closed position can be as small as 4cm2, this then immediately over speeds the turbo causing boost to rise and open the vanes again, this 'kangarooing' effect can make the car undriveable.
There are NO VNT systems in production that do not at least electronically modulate the pressure actuator for this reason.
The most promising solution I have come across is over on competitiondiesel forum IIRC where a guy used drive pressure to control the vanes, works well but you don't get to choose boost pressure, the turbo just runs at its sweet spot of preferred exhaust manifold pressure equilibrium.

H
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