I have been thinking a lot lately about how to go about adding power to a stone-stock platform; Subaru WRX or EVO VIII mostly. At the core of my mental tug-of-war are two philosophies of tuning-freeing and generating.
These mindsets may seem opposed based on the aggressiveness or lack of aggressiveness behind each but very often freeing is the launching pad for generating. With the big-power promise of the generating camp one loses the inherent reliability of the freeing method. Tuning is, and always shall be, an endeavor governed by compromise.
Freeing is a milder, basic bolt-on version of tuning wherein factory restrictions are eliminated which results in the freeing or "unleashing" of power. In turbo applications we are talking about downpipes, up-pipes, high-flow cats, exhaust systems and intakes. Depending on the design and condition of the OE pieces there is a great deal of power potential hiding in the background. These proposed mods address pumping losses, i.e. the amount of work the engine has to exert to expel spent gasses through the system. By easing the losses more power is freed to work the tires. Some parts, like downpipes for instance, can also impact boost by moving gasses through the turbine and past the wastegate more efficiently, which can add a pound or so of boost at peak. The final player on the freedom side of the ledger is the almighty boost controller.
The boost controller is the crossover modification. You can ask for more boost but must consider the capacity of the stock fuel system, the tuning regime of the engine, the efficiency of the stock intercooler, and remember engine reliability is at stake. So watch that air/fuel ratio.
Generating is scrapping some of the more critical parts and systems on the engine and adding bigger, better (prettier?) parts in their place. Folks in this camp swap out turbos, move to more aggressive cams, enhance the fuel system, upgrade the tuning strategy, put the whip to that boost controller, and employ forged internals to stand up to the challenge.
An unfortunate byproduct of this big boost infusion can be felt, literally, in the drivetrain. Depending on the car and its intended usage a good deal effort and money may need to be invested in this subsystem.
The boost-induced adrenaline rush that is an aggressively tuned turbo car pulling at the reigns in anger is profoundly tempting. When it works it's awesome. The key is to know your car, know your budget and be ready to exercise a truckload of self-restraint because once you start feeling that free power it's easy to get "launched" into the generating camp.
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