"Turbos use power that is otherwise wasted out the exhaust pipe"
Arrrggghhhh... I really hate it when people say that when they are comparing them to superchargers!!!
Its a load of crap...
Putting a turbo on an engine robs a fair bit of power, its like having an extremely restrictive exhaust. It causes a lot of back pressure between the engine and the turbine which makes it harder for the exhaust gases to leave via the exhaust port and so a greater volume remain in the cylinder after the exhaust valve has closed. This means that the combustion process is less efficient, because this gas takes up the volume that should be filled with fresh air/fuel mixture. However the Turbo is forcing in additional air and so that outweighs the losses due to the added backpressure.
It doesnt however mean you are getting something for nothing! I think the fact that a lot of companies that are fitting aftermarket turbo conversions seem to think this is the case shows their knowledge is prehaps somewhat limited!
While Im on the subject... a Rotrex supercharger, which is basically the compressor side of a turbo mounted to an extremely efficient planetry gearbox that runs off the crank pulley, will sap less power than the average conventional turbo and it wont generate anywhere near as much heat which means that average intake temps will be lower which again means more power.
If you look at the turbod and supercharged Saxos as things stand at the moment the supercharged ones are getting better power figures even though they are running the same levels of boost.
Another thing with turbo is they spin up at a set rpm and only produce max torque for a very limited time before it starts to fall away. For most smaller road going Turbos every time you change up a gear you are actually using less and less of your peak torque and as a result you arent accelerating as quickly...
The only way to get round this as they do in motorsport is to use a large turbo that spins up at high revs and so you get the full effect of the torque in every gear... only problem with that is massive lag, which realistically isnt great for a road car, especially one not designed for the stress a turbo will put on it.
You only have to look at a power graph for a Turbo car to see that there is a very large change in power over a very short space of time and thats what puts a strain on pretty much every component in the engine and transmission. think about the easiest way to break a piece of string, you can apply a big force over a long period of time and it wont break, but yank it quickly and itll snap. Plus turbos generate a lot of heat because the spin upto such high speeds and again that will put extra strain on the engine.
Superchargers have their downsides as well, its just I cant think of any right now... Well apart from the fact that ultimatly they wont generate as much boost as a turbo, but in most cases that wont be the limiting factor itll be the strength of the engine and gearbox that dictates how far you can go.