[olddog]

At first thought, I assumed the reason aluminum blocks made less power was thermal conductivity. Aluminum will transfer heat away at a much higher rate than cast iron. Then after thinking about it, these are sleeved engines and the cylinder wall is typically ductile iron or some other iron. So thermal conductivity is not it, but it does matter on heads.

Seal issues is what I have read. If true then a sleeved cast iron engine may have similar issues. I honestly do not understand why this may be, but I do not question the observation made by so wide a group of engine builders.