Torque + Fuel economy

You can get more torque from the slanty, but normally aspirated, to be significant, it comes at a price of more rpm, more stall and more gear.
All of these run counter to better fuel economy.
Torque + fuel economy, is a tough nut to crack.

Chrysler figured it out pretty good with the lean-burn SYSTEM, and the Dart-Light cars. It's all about light weight, Effective cylinder pressure, and a tiny 2bbl carb with lots of airspeed thru it at low-rpm.. Their only shortcoming was the lack of adequate timing.