When you Turbocharge an engine you give it more air, which has the effect of heating it and causing it to loose its density. The reason being that when you Turbocharge an engine you give it more air, which has the effect of heating it and causing it to loose its density.  This is why an intercooled Turbo engine is more efficient than a standard Turbocharged engine.  An intercooled Turbo engine puts out ± 20% more power than a standard Turbocharged engine.