So I realize that the engine produces pressure but most of the time this pressure is 1:1 with the boost pressure when the turbo is actually doing its job (higher engine speeds/loaded). This raises the question about how you can gain efficiency if the boost you make is used for drive pressure which means the pistons do have a force to shove the exhaust out to drive the turbo. Now a book I have says it also uses the heat from the exhaust which is apparently one of the key factors in reaping the benefits of a turbo. My question is, how? I wouldn't think hot air on it's own would do anything at all. But the pre and post turbo temperatures are 300F apart so apparently it's using it somehow, I just don't get how. Anyone care to enlighten me?