in 2012 mazda released their SKYACTIV engine that runs 13:1 on 87 octane. So i agree with funwithfuel, there are more parameters that have to be considered.
Yeah. I'd check to see if the old Dodge has a DIG (direct injection gasoline) engine or not! The SKYACTIV Mazda engine is so far removed from what you've got there that there are no comparisons you can make. None at all.
