So you want to start tuning ? Where do you begin ?

"Power is nothing without reliability".
So whats the point of buying loads of tuning parts, strapping them on and winding up the boost if the rest of the engines on it's last legs ? It won't last five minutes.
The rest of the engine must be up to the job if you want it to last.
Good build quality and attention to detail will make a reliable engine not necassarily the most expensive parts.
A Turbocharged A-Series can be made to produce over 200+hp and 180+ft/lb of torque, So the potential for power is huge. But obviously at this kind of power output the life of engine will be reduced, even if parts do not fail the engine will need regular overhauls to replace worn components. This may be fine for a race motor, but for a road car most people would like a bit more mileage from their engine before a rebuild.
Basically the higher the power output from your engine and the more often you use that power, the sooner the engine/transmission will need overhalling.

For information on building a strong motor check out the Engine Building  & Transmission sections.

To create power we need the engine to consume air, this when mixed with the correct amount of fuel provides the mixture which is compressed and combusts in the cylinders. In order for more power to be made we must make the engine consume creater amounts of this mixture. To do this the path the air/fuel mixture takes into the engine must be as free flowing as possible. So basically anything which restricts the flow in some way, will in theory harm power output. It is also the same for the exhaust side of things. This needs a free flowing exit so the spent gases can leave the engine, and a new fresh charge can enter the cylinders. We have the benefit however of being able to force the intake charge into the engine via a Turbo charger. So slight restrictions do not harm power quite as much as they would on a normally aspirated motor.

Tuning 2.