If you're looking to increase power, the first thing you need to get is a tune if you don't have one already. You'll get the biggest power gain just from a tune alone! Without a tune, you'll see virtually no gains from other mods, especially a cat-back exhaust or air intake. Those two mods will give you the least amount of power gain out of all the mods available... So if you'll looking for real power, you need a tune, cat-less downpipes, bigger intercooler, turbo inlets with new filter system, charge pipe and BOV... do things in that order, and you'll be in for a huge surprise
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2009 Z4 35i 6mt, SpeedTech 6266 Gen2 turbo kit, Tial WG, VRSF 7.5 race IC, ER charge pipe, Tial BOV, Radium Fuel cell w/ surge tank and twin Walbro 525 pumps, Radium FPR and return line, Bluetooth ethanol sensor, Phoenix intake manifold w/PI, JB4 tuner, PR coil packs, Custom oil cooler, ECS Radiator, Spec 3+clutch, Mfactory flywheel, single 3.5" into dual 3" exhaust, H&R springs, 19" TSW wheels, 235/19 & 275/19 RE11 tires