...as far as i can see my EEC4 cover is the same width as the 4x4 one.

4x4 = 460bhp

EEC4 = 520plus bhp

So the xtra power is gained from the bigger elbow on the EEC4...quite obvious!....SO it seems the elbow size is the restricting factor....so how does putting a spacer on have any difference in bhp capability to a 2wd/4x4 cover?