Basic Performance Upgrades. These modifications are: A full length three inch down-pipe (with or with-out high flow cats), 3″ (75mm) or bigger cat-back exhaust system, raised boost (18psi), and the required boost cut eliminator (GReddy BCC) needed to achieve that boost without activating the factory fuel cut-off at 14-15psi. These are the modifications that have proven to provide the best HP-to-$$$ ratio.
What does the + mean when someone says BPU(TM)+? And what is APU?
That stands for any additional power producing modifications other than the basic BPU(TM) modifications. One “+” refers to Adj. Cam Gears and under-drive pulleys, the second “+” refers to a Fuel controller, ECU upgrade, etc. For instance, a Supra with the BPU(TM) modifications, plus a front-mount intercooler, would be called BPU(TM)+. If you added cam gears to that, it would be BPU(TM)++, and so on. The “BPU(TM)” term is used until you have an upgraded turbo(s). Then it is referred to as APU, advanced performance upgrades. This designation pretty much covers every modification that can be performed.