I've become a huge sceptic of NA petrol chip tuning over the years, and nothing I've seen since I stopped chipping my cars has made me change my mind. But I suppose genuine 2-5bhp claims will never sell a £400 plug-in chip costing £5 (no, there aren't millions of pound of development spent on the software, it will be one guy spending a day on the rollers when a new car comes out and then selling the resultant chip as a masterpiece - so £500 to recoup in development costs).
Certain tuners claim that all the S54B32 cars only have 320 of their claimed 340bhp on their rollers, so I assume when they give you the car back with 345 you'll be over the moon, but never considered finding out why your nearly new car is that much down on power in the first place (is it down to their rollers/calibration/marketing, or are BMW falsifying power claims).
It's also strange how (for the same mods) Evolve claim 15-40bhp for the e46 M3's S54 yet only 10-25bhp for the Z4M's S54 - and I notice their dyno chart for the 'stage 1' kit shows a 24bhp peak gain, but the note on the image says it's 'stage 2' and it makes the power delivery more lumpy, and the run is done in '3rd gear' (again according to their chart - which I'm sure will be put down to a data entry error). BTW, I see no mention of raising the rev limit, yet their chart shows the peak power being at about 8150rpm.
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It's a similar story with Evolve's e34 M5 claims (which is where I know them from originally). They state they'll give you 25bhp (but only at a certain point around 6000rpm), they also state 20bhp at 3500rpm (the graph does not support this BTW) and only 10bhp peak. They also raise the rev limit by 300rpm to 7500rpm which any decent e34 M5 tuner will tell you straight away is a recipe for disaster - but I assume they've a warranty in place for that eventuality.
In fact said:
The E34 M5 3.8 must be tuned carefully with special attention paid to the rpm limit. Raising the rev limiter on these engines is not advised.
And yet they go and do the very thing they advise against.
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So, whilst I'm not saying remapping will not make any gains, make sure you understand how these gains are being made (i.e. if they claim better fuel economy whilst also giving more power at every point, then it's bull). Ask where the peak gains are and whether this remap is for fuelling only, or are they matching the VANOS to these new peaks and troughs? 20bhp sound good, but if it's only over the last 500rpm then it's a waste, and almost 30lb/ft is phenomenal and I'd be happy with just that without any BHP increase.
Personally I'd get 3 rolling road runs done on 3 independent rollers (preferably the identical model) to get an average (and to let you see the different figures you can get from 'identical' set-ups, and then go back after the remap's been done and do the same thing again. Take the average figure of the 3 before & afters and that's what you've got - I'd be happy to map the data into Excel charts if you wish.
