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Not sure how other vehicles are set up, but as I understand it the VNT/VGT generally speaking acts like a small turbo at low rpm & load by closing up and opens up fully at high speed/load, this gives better torque across entire RPM range. If the relationship was just engine & turbo, it would be a simple affair, but when you add in the emission controls like EGR particularly, then the ECU starts playing with the VNT to achieve a set of pre programmed parameters.
I did monitor the VNT solenoid for a while to get a handle on how and when it opens/closes & even went with a PWM unit for a while & bypassed ECU control of the turbo.
I removed the external intake snorkle recently and set up a cold/pressure air intake from front of vehicle, this helped significantly with both engine response & EGT's are down 20-30C as well as dropping boost about 2psi, there have also been other mods going on as well, but the cold/pressure air intake was a major improvement.
I know this proposed mod will also help, as I have already tested it, but to quantify improvement is not so easy.
One of the other things I have been pondering is would it also help coasting down if the intake was restricted a bit at the same time as opening the exhaust, so reduce air going in as well as free up air going out, what would be the ideal free coasting diesel engine set up in gear?
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