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Discussion and questions related to the course Practical Diesel Tuning
I've been looking for a timing calculator for this setup but so far have found none. In thinking about this I considered that stock injector's capacity is rated at 135cc (per 1000 strokes). I've upgraded to a 175cc capacity injector but with +30% nozzle, so seems to me that the 30% increase in capacity is offset by the 30% larger nozzle, thus the full throttle injection events should occur at about the same time as with the stock injectors. The thinking is that 30% more fuel is discharged 30% faster. It seems that with part throttle events however, the same amount of fuel required to maintain a given cruising speed would be delivered roughly 30% faster, so under these conditions the SOI event would actually have to be retarded from what the factory tables have (had) in order to stay within the injection window - hoping to achieve the desired 50% of the injection event occurring ATDC. I need to revisit that part of the course I guess to understand better how to calculate these event but hoping someone can check my thinking. It seemed counter-intuitive the first time I thought this through.
I like that you've taken the time to work the theory out in your head to this degree before taking to the tune editor. There are a couple of things I'll mention that you may find useful.
1. You're not likely to hurt a diesel by significantly advancing or retarding timing at light load. What I mean here is that if the truck is making less than 10psig boost - don't be afraid to experiment.
2. Your ear, nose and eyes are going to be very useful in validating your theory. If timing is too advanced you'll likely have a clean running truck that clatters more than you like. If timing is too far retarded, you may smell fuel or see a trailing haze of grey smoke under normal cruise (you'll also have high egt's for the load).
3. The factory timing number as a starting point for your theory is fine, just understand that they arrived there for emission and NVH reasons, not necessarily for maximum efficiency. The factory is always on the retarded side of max efficiency.
I'd suggest driving it on the factory table and noting your observations as you experiment up and/or down.
Hope this is useful,
I guess I'm a little paranoid having seen photos of bent connecting rods and melted piston heads allegedly due to over-advanced timing. Seems I remember reading somewhere else that maximum torque (and thus efficiency) with maximum cylinder pressure in the 10-16 degree ATDC range but without a cylinder pressure transducer, finding that sweet spot seems tough. I'd be a little more confident if I had access to a chassis dyno but for now I don't. I wasn't sure where that danger point is with regard to load and over-advanced timing so thanks for that approximation. Clatter by itself is of little significance to me since, well, it's a diesel! LOL. Excessive clatter as the result of too much timing though certainly is but I'm not sure where that would be - on the basis of noise alone. The pilot injection can do a lot to soften this at low speed/load so for now I've turned off the pilot injection hoping to make ignition clatter a more useful reference. The OE strategy is to turn it off @ 1400 RPM or pedal position above 40 and it definitely makes a difference in the sound.
Running OE tuning with these injectors has anomalies, probably due to the fact that they plug the spill ports as a way of increasing the injector capacity. Idle problems and return-to-idle strangeness shows up, which I've been able to partly correct by increasing ICP (injector control pressure) a little. I think there's probably a better way to do this with FICM tuning, I'm just not there yet.
With all of the aftermarket tune files I have there is a light haze during WOT runs but I'm not sure if it's reasonable to expect to be able to eliminate it completely. It does get 30% more fuel than stock. I'm limited with boost pressure because of the plastic intercooler. I think I'll do some logging of some of these other tune files and try to use them as comparisons. The aftermarket tunes are encrypted so looking at the actual tables isn't an option. I'm not sure if I can do better power-wise than they've done but I *know* I can fine tune the transmission operation to my liking and *hope* to be able to improve economy as well.
Thanks again for the reply and for bolstering my confidence a bit!