Bruce - a hell of a lot of tech at that place with the link.
I suppose I have assumed that the common rail pressure is on a bit of a ramp across the throttle pedal travel range, with the fine tuning of the piezo-electric injectors having the fine control of fuel addition via their opening and closing up to 6 times per combustion event, rather like a tap on a mains pressure pipe. I thought that the box worked simply by upping that rail pressure ramp profile right across the throttle range.
To me that explained how the same power was achieved on a smaller throttle pedal setting when the box was on.
The Spider box talks of 20,000 calculations per second and a delay of less than 0.1s from normal to full load. To me that suggests that it works slightly differently by allowing the ECU to make a fuelling decision via signals and the box then decides what action to take to increase the rail pressure. If it detects small changes over however many calculations in a fraction of a second, it may decide to leave the ECU's signals unmolested, but on the larger changes it decides to intervene and up the rail pressure (that's my understanding of it, rightly or wrongly).
Their technical descriptions etc "seemed" a little more honest on their website. They say that their boxes don't provide mpg gains, nor do they claim to because when not under more than moderately low load demand it allows the ECU's unchanged signal to get to the common rail. They also said that other box tuners mpg "gains" come from the permanently increased rail pressure fooling the ECU into thinking the car is using less pressure than it is. This rings true because my TDI-tuning box appeared to be more economical (indicated), the higher up the settings you go, but actual mpg stayed the same or worsened.
Having the car operating within it's normal rail pressure parameters when not under much load seemed advantageous for smooth idling. I'm more worried aboout the longevity of the injectors than the common rail itself if the fuel system is constantly under increased pressure, rather than when just under mid/heavy load.
It could all just be patter though. Spider also claim to supply some main dealer marques for semi-official upping of the output. The description of how they claim the box works seemed so much more sophisticated, especially if it does operate on a process/review and act accordingly basis rather than a fixed system of throttle pedal load A, causing standard common rail pressure B is modified by the box to cause modified rail pressure C.
They've got excellent guarantee coverage and it would seem that the box can go onto another car without reprogramming, as long as the wiing loom connections are the same.
Right now my car seems a lot livelier on Esso (without the box),albeit only 4 miles in, than it did on V-power (without the box). Hopefully i'll see mpg increases too. I'll give it a few days and decide whether I really want the box, if the use of normal diesel brings performance closer to expectations than I was seeing before.
