Hmmm, I thought I'd already responded here, but obviously not.
There are essentially two kinds of chips. The cheaper ones are single function, mostly rail pressure but some control duration of the injector pulse. Then there are the good ones which monitor and control multiple signals including everything from manifold pressure to exhaust temperatures. These are almost the same as a reflashed tune, often better because you can have multiple tunes that you can use according to what you're doing.
The chip you linked is a single function unit that is sold for a very high price. Increasing rail pressure certainly works to improve performance in a diesel, but it's not the only thing and some have come unstuck with this kind of chip because it isn't a balanced solution. Just as an example, air fuel mixtures can become over rich and cause internal engine damage (often to pistons) or just bump EGTs so high that the car goes into limp mode to prevent further damage, something that could be very likely with long heavy pulls uphill. Of course, bigger exhausts just make the problem worse.
The better chips monitor and adjust all these things, so the likelihood of terminal damage is much lower. They are also tuned to a specific vehicle, on a dyno. The results can be astounding, and the tuner knows his craft, very effective at achieving the customers' needs.
But, they're comparatively expensive against the cheap, single function chips and there have been innumerable cases of "I want more performance but I don't want to pay the price".
Reality is that you get nothing, or worse, for nothing and the technology, plus multiple dyno runs to tune a good chip doesn't come cheap. Expect anywhere from $1500 to $3000.
Examples of good chips? Unichip and Chiptuning have good products and they can dyno individually, not just hand you a dyno results sheet for a tune developed on someone else's car. There are others, of course and there are still some very good chips in the secondhand market that can do pretty much the same thing.
What can you expect? For the single function chips increases in power and torque of around 20%. For multi-function chips power increases of around 35% are fairly common while torque can increase by around 45-50%. Vehicle specific tunes can give a lot more than these numbers. My 4M41 achieves 0-100km/h times of 7.0 seconds on a mid-range tune. That's only 0.6 seconds slower than the legendary GTHO Falcon, from a vehicle with a weight of 2.7 tonnes. It has more torque than an LS3 V8. That's all done with two Chip-It chips and an extreme performance tune can shave another 2 seconds off that 0-100km/h time.
kevin wrote:And now that last response was by using "POST A QUICK REPLY"; very strange!
Yes, we know. An intermittent problem in the forum software. Just use the "POST REPLY" button. Meanwhile I've deleted your test posts. We do have a sandbox for that.