I guess nobody had fully comprehended what I was attempting to say. That's my bad. Please allow me to try again. The same engine with a supercharger or a turbo will always make more power at the "Same" level of boost when running the turbo option, because the turbo does not use any of the crank horsepower to drive the compressor.

True, you can make more boost and additional power by either spinning the existing compressor faster or installing a larger compressor. Eitherway, you use up a significant amount of horsepower just to spin the screws in the supercharger. That is never the case with the turbocharger since it is driven off the hot exhaust gases. It is very true that turbos concentrate heat in the engine bay and that must be dealt with. But heat is potential horsepower and if you can put it into the engine, you can capture at least some of it at the wheels.

Another somewhat unrelated observation that I have made is that in hotter ambient temperatures, a turbo car is affected less than a supercharged or N/A car. When the air is hot, less dense and the oxygen molecules per cubic foot are lower, most N/A or supercharged engines make less power. That is because no matter what else you do, less air is being forced into the cylinders under hot ambient conditions. In the case of a turbo, they are also affected but since they are controled not by the speed of the crank but by the exhaust and the wastegate, the only major difference that I have seen is that it takes more RPM's to reach full boost and to a lesser degree, it sometimes will make less boost for the same conditions unless the boost controller is adjusted. The same thing takes place if you drive to a higher altitude. The turbo suffers less power loss. That is why when adjusting for Density Altitude, the turbo cars get less compensation.

If you track the absolute pressure on the intake tract of a supercharged car, it will always make less boost at hot temps because it is spinning at the same rate regardless of outside temps and there is no practical way to adjust that. On the other hand turbos have a sort of self adjusting system so they can partially compensate for this within a certain range of operating conditions. I have an old turbo bike that runs about 17 psi boost. At sea level it takes 4000 rpm to make full boost. The same bike at 6000 ft elevation takes ~6000 rpm to reach full boost. Once up to full boost it runs just like it did at sea level, while its N/A counterparts are sucking wind. At some elevation height, it would no longer be able to spin the compressor fast enough to make full boost, but at least where I live, that is not an issue.

Irish