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Originally Posted by Tesla
The first question is, under load increased pressure to turbo is good, but when coasting down, no load, will the engine run more freely if I also restrict the intake, noting I already open the VNT fully to allow a more free exhaust flowundere this condition?
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A colleague of mine worked on that engine extensively during development. Interesting question. I think you actually want to supply pressure, or at least not a depression, during overrun as restricting the airflow will only increase pumping work. We sometimes apply an intake throttle to increase engine braking which I guess is the effect you're trying to avoid.
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Originally Posted by Tesla
The other thing that I am exploring is whether running at lower boost will give better economy figures, provided the EGT's stay in an acceptable range, is this the right direction?
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I would have to look at some data, but generally the base cal wouldn't be demanding (or achieving) too much boost at most conditions. You really need to keep the AFR up as combustion efficiency will worsen as you go richer, certainly when you get down below 25:1 or so. For reference, you'll be getting visible smoke (if no DPF) below about 22:1.
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Originally Posted by Tesla
And in general, any pointers for achieving the best economy from a modern diesel engine?
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I'd focus on keeping max revs below 1800-2000 rev/min as a starter. I'll dig out some typical BSFC maps if of interest so you can see where to run.
James