A quick search pulls up a few different options, the BMW JB4 of course, which seemed to pick up around ~120hp from the one graph I saw. Also read about an Active Autowerke Active 8 Tune which appears to be a piggyback as well and they claim 60hp/90tq gains yet cost 130 dollars more? Lastly, and I know dinan usually isn't very potent and is typically very over priced, but I did notice they have the DINANTRONICS Sport Performance Tuner for B58 engines which is supposed to be shipping this month. Considering there aren't many options available I thought I'd include it, here are some shots. Who has the JB4 on their B58/B48?
