How much power does a turbo take?
Recently when browsing through this technical forum I have noticed the topics of supercharging, turbo charging and the problems posed by “lag” being discussed.
I recall the question being raised, how much energy does blower actually take from an engine? Whether “blower” was meant to mean supercharger or turbo I am not sure. When asking the question “how much power does a supercharger take?” the answer must of course be “a bit of horse power, after all you can’t get something for nothing!” This is because the compressor is powered mechanically by the engine but the added volumetric efficiency more than makes up for mechanical loss.
However, has anyone ever thought how much power a turbo takes away? A turbo consists of a compressor which is powered by a turbine which is propelled by exhaust gasses. Although it sounds strange and I am sure not every one will agree with me, a turbo could be looked upon as a second engine altogether. One could say it is a gas turbine engine which is mated to a piston engine. In a piston engine mechanical power is produced by the expansion of gasses in the cylinder. But it is also true that the turbine in the turbo is an expansion engine too. The exhaust gasses are hotter than that of the atmosphere after all. Think of it this way, a gas turbine engine can reach very high power levels, massive when compared with that of a piston engine. A turbo is merely a gas turbine which bleeds off most of its power to a crankshaft, via some pistons in it’s combustion chamber (a number of cylinders).
Once a turbo is viewed from this perspective, one realizes the question “how much power does a turbo take?” is irrelevant, as it is an entirely different engine altogether. This point is backed up by the fact that rally teams often introduce fuel into the compressor of a turbo to reduce lag. This may be achieved by cutting the ignition briefly or directly spraying fuel in!
I should point out that Keith Duckworth (founder of Cosworth and very bright chap) used this argument to try and ban turbos from F1, as gas turbines and two engines were both banned at the time. It was only after reading of this in a book that I realised just how much turbos and supercharged engines differ.
Last edited by M Doe; 07-02-2004 at 09:26 AM.