turbo is not free power
Turbos are not free power, as some will claim. A turbo is a turbine-driven supercharger and to drive something requires horsepower. The turbine needs velocity, volume, heat and pressure to operate. The first three won't make any boost. It's pressure that makes boost. The first three help with greater efficiency. The pressure in a turbo is measured by the difference in intake manifold pressure and exhaust manifold pressure. This is referred to as the exhaust-to-intake pressure ratio. Most turbos operate at a 2:1-to-3:1 ratio, meaning that if 10 psi is in the intake manifold, the exhaust manifold will see 20 to 30 psi. (The GN operated on a 2.5:1 ratio and the 300ZXTT had a 2.7:1 ratio). Some racecars make PR better than 1:1, but they're still making backpressure. Backpressure is a restriction, and a restriction is not free power.
Thus why the word "free" in reference to the turbocharger boost was in quotations, to indicate that I was simply referencing, not laying claim.
I fully realize that you can't get something from nothing (Which would be the full application of the term "Free" in reference to boost generation), but the turbocharger is still more efficient even if only by sheer virtue of a reduction in the number of state changes that must be made to supply the desired output.
It is also "Free" in that it tends to avoid a great many of the parasitic loss points associated with mechanically driven forced induction setups, such as the belts, pulleys, gears, chains, or whatever else you use to drive the setup. Yes, you have the increased exhaust backpressure over a mechanically driven supercharger (which places no restriction in the exhaust), but this is offset by other factors which increase the turbocharger's efficacy over the supercharger under the conditions where the turbo is more desirable (typically, mid-range and top-end power. I don't think I've ever seen a turbo used to boost low-end power specifically).
