Engine blocks used to be made of cast iron, but they&#x27;ve pretty much all moved to aluminum because of 1) weight, and 2) that higher thermal conductivity.  IANAME, but IIRC the problem with iron&#x27;s lower thermal conductivity is that it created hot spots which could cause pre-ignition, so you had to use lower compression ratios to avoid this. Aluminum has more uniform temperature so you can boost the compression ratio, which gets you more efficiency and power.