with a ecu and injector upgrade you can be as fast or faster than a stock vr instantly.
With just an ECU upgrade they're quicker than a stock VR... Not top end though... They don't seem to do high speed particularly well - Assume this is down to gearing.
A 130bhp 1.9 TDI goes to 185bhp and 285lbft with just an ECU map and a panel filter.
With a hybrid turbo, ECU upgrade and Injectors, they're fucking mental.
Like 400+ lbft and 250bhp etc
Run it on decent diesel (Over here Shell has an Optimax equivalent diesel with high cetaine rating) and it gets even better.
Whoever maps the ECU has to be shit-hot though, or else EGT's go through the roof and you get a shit-load of smoke.
Big Intercoolers help a lot... I didn't change mine, but in the summer you could really feel it struggling. 95 Centigrade Air Intlet Temperatures were common in the summer when the little stock IC got heatsoak.