Free Mods? Hmm? Every Mod I have done has cost me something. For me the foil Delete was quite easy. A cordless Drill and a Wire Wheel. Really gave the tube a polished look. Took about 20 min-->Total. Hardest part was taking the tube out and installing it back. Cleaned and Polished. I'm sure I gained 5 more HP. Maybe!!
ZooDad? -->That idea made me go by a new Intake. Not Free! But Nice Insurance. Really a great Filter system.
Free Mods--->Keep your air filter and housing clean and Intercooler and radiator clean and clear of debri & Correct Tire Pressure. I would say good maintance habits, but that's not ever free.