[Tesla]

Thanks for the responses James,
Just the sort of info I've been trying to get

Originally Posted by jmcc

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.

With the overrun/coasting, I was thinking that there may be a minimum pumping losses point where the suction (under mild restriction) required on the intake stroke was balanced by the forces required in the compression and exhaust strokes, knowing ofcourse that the exhaust system itself has ideal flow requirements to help draw the exhaust out of the engine.

Originally Posted by jmcc

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.

Running with the VNT fully open, which is effectively then a Turbo sized for High rpm on the ZD30 engine, around town it is virtually no boost, but seems like torque & power curves drop to a lower rpm range, and also drop in an absolute sense. On the highway at 100-110km/hr 2,500 to 3,000 rpm it achieves 3-5psi, I do not see any visible smoke, my gut feeling is that the ideal spot for fuel efficiency is somewhere between the ECU settings and the fully open VNT. I did notice an increase in EGT's with VNT fully open, but that's another question of the EGT drop across the turbo, my pyro is mounted post turbo and I hear the drop in temp is variable and dependant on Boost pressure, rpm, load etc. eg at idle may be no temp drop, but at high boost & load could be 200-250C.

Originally Posted by jmcc

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

Definately interested if you can dig up some relevant BSFC maps, still reading up and getting my head around the whole BSFC story.
I will give that a try, with this engine max torque is around 2,000rpm and I find it is quite comfortable to drive around that rpm, except at higher loads when it really cranks up at the 2,500 - 3,500 range.

Originally Posted by jmcc

Oh, and if you can disable EGR without tripping a MIL then that's worth a couple of mpg straight out (to the detriment of NOx, but hey ho).

Have been toying with that one for a while, i know it is better for the engine in terms of longevity, but wanted to get a better idea re economy. Is this generally true for all diesels, or all engines for that matter? I surmised that there may possibly be a reduction in pumping losses, by pushing exhaust from one cylinder directly into the intake on another, like a bit of a balanced closed loop idea, but your opinion tends to sway me more towards the negative effects of the EGR system.

Thanks again James,
great information and sorry for picking your brain with a jackhammer, just been starved for info on this particular topic.