This is one of the first projects we’ve covered from the lesser known tuning company ATT-TEC who have done a good job with this BMW M3 convertible. By giving it an increase of power with a G-Power tuning kit, the stock performance numbers have seen a jump from 420 PS to 520 PS or 513 horsepower. This is a significant boost for the price of only €11,430 or US $15,000. Installation from the ATT-TEC tuners will run €1,310 or US $1,720. These prices do not include the new coilovers, wheels or exterior styling parts which we’ll get into next.