@1seriesstud: You thought this whole time that piggyback tunes on 135i's stacked??? Ok now I know you are new to the E82 tuning world
Just messing with you...but like the others have said they do NOT stack but instead fool the car into thinking it has lower boost and then adjusting timing and other parameters to run at what the boost level actually is.....JB4, Procede both do it although in slightly different ways (an entire argument on its own). Will a tuned 135i with piggyback and full exhaust and IC mods be fast in a straight line? You bet your ass it will...esp. if they both hook up off the line properly...no way a retooled intake, exhaust, flywheel, and LSD beats my car with 60-70 more WHP and 70-80 more lb/ft of torque.