are there any materials that alternate between ferromagnetism and diamagnetism?
All materials that aren't effected by a magnetic field can be considered diamagnetic to a differing degrees. In the making of Alnico magnets , which are rather strong ferromagnetic magnets, the three elements added are aluminum, nickel and cobalt (that's where the name alnico comes from). All three of those elements are diamagnetic separately, yet combined they are very ferromagnetic The same occurs with the rare earth magnets. Neodymium alloy (Nd2Fe14B) is made of neodymium, iron and boron. None of the ingredients by themselves are ferromagnetic, but are extremely ferromagnetic (except iron) when the elements are combined
If you start removing exhaust parts without tuning your engine to the new exhaust set up you are not likely to gain anything and might even loose power.
Your exhaust is actually a way for the motor to slowly cool itself. When you turn your motor off the exhaust and the motor are still hot. Cool air cools the full exhaust then slowly cools the motor. The exhaust tip and possibly the muffler are ok to remove. Keep in mind the vehicle will become alot louder. If you take the catalayic converter off though that will cause your exhaust velves to ward then youll have a serious problem.
