Just got thinking about this. I'm sure Jarod is right - 4.2 is the limit for this engine - cylinder spacing in the block is tight. Audi would need to re-tool and basically make a brand new engine to get more capacity = very expensive.

Also piston speed is already at its limit at max revs to there can't be more power to be had by letting the engine rev higher.

This only leaves an increase in torque to get more power. To get 10% more power you need 10% more torque. Not being an engineer I don't know if this is possible but there was speculation that ValveLift combined with reduced internal engine friction (new materials) could give this extra kick.

To get more low down torque and better fuel figures a forced induction 4.0 is the better solution but I'm not sure Audi care so much about this for the RS cars. Can't wait to find out. I'll be looking seriously at the next RS4 and I'm sure this RS5 is going to give us a preview or what will be in the B8 RS4.

Marv