[BongoBennie]

Originally Posted by serialk11r

Ehhhh...
Forced induction often does not result in a lighter engine. Often times they throw in heavy iron blocks which ruins any sort of weight saving. For example the iron block 3S-GTE weighs more than a 3.5L 2GR-FE (with a cam swap easily makes well over 300hp). Turbo/supercharger hardware can add 100 pounds to an engine that was only 250 pounds to begin with.

To get a high power/weight ratio engine you first want a small stroke, maximum possible revs, and then very high boost (hey what do you know, F1 is running the smallest possible stroke, as many rpms as the regulations allow, and when turbos are around, as much boost as possible). With the <1 bar boost that most cars have the turbo barely adds to the power/weight ratio of the powertrain, especially because of the increased torque which needs a stronger transmission.

Now you can nitpick and say certain setups such as a centrifugal supercharger are extremely light, but forced induction is typically going to lower the engine's thermal efficiency under load.

Anyhow my point is naturally aspirated engines are used in racing for a reason.

The idea of turbo engines being lighter is that you can use a much smaller engine.

http://www.youtube.com/watch?v=fqqJs0mqH9M#t=143