Just to add my two pence worth

I guess all you MLR members know what I have fitted to my E6

I did look at the SPA design instruments but I decided against them as they were digital readouts which are not ideal to read quickly (as Evoboy said). It is difficult for the human brain to comprehend a digital readout whereas an analogue needle is easy to get a rough idea even without knowing the exact value. I decided against HKS and the like due to the price, I don't want to pay an extra £60-£70 just for a brand name. I also looked at Racetech dual gauges which are analogue but the fact they were cheap mechanical gauges put me off, also they didn't do a dual gauge featuring boost readout.
The Defi appealed to me because it was good quality, comes with virtually everything to fit it included, is easy to fit, very easy and cheap to add extra gauges to it with the same functionality and above all was great value for money.
If you want a decent gauge then you can't go far wrong with the Defi-Link system, if you want a decent gauge and to match the illumination then look elsewhere but expect to pay more for it (A'pexi do a blue illumination gauge suitable for the E6).
As for kgfcm2 then as has been said it is only 2% difference to bar or in other words there is a 0.02bar difference for every 1kgfcm2 read! If anyone can spot the difference over 2 kgfcm2 then they will have to have bloody good eyesite!
For those who are really worried then Defi-Link Boost gauges are also available in PSI if you get the American version.
True the playback function is not that important with just a boost gauge. Add other gauges to the system though and it becomes more useful as you can playback the whole lot at once. It will never be as useful as datalogging though but then again it never was intended to be. I looked at the playback functions as an 'extra' to the more useful Peak mode and Overboost Warning light which was the minimum I wanted.
I got my gauge from
Newage Motorsport. MLR members have a look in Wastgate Chatter for the special offer that is available. For everyone else it's £139 inc VAT |PLS| P and amp;P
Sam,
Defi HUD displays are illegal on UK cars, just a warning come MOT time if you get one
