[userbinator]

The difference is that tuning an IC engine is pushing components into/past its designed safety/mechanical thresholds.

It's not uncommon to find models with a wide range of power outputs but the exact same mechanical parts, and the only difference is the program in the ECU. Before electronics, the difference might be in a few small parts[1]. If you spend long enough staring at parts catalogs you can easily spot such things.

[1] One of the examples that immediately comes to mind is with diesel engines --- you can change the fuel injectors to tune power over a very wide range, limited only by your acceptance of fuel consumption and emissions. All the load-bearing parts of the engine (block, rotating assembly, etc.) are exactly the same: http://forums.aths.org/Attachment20581.aspx