[Richard L]

If you can push up more power per litre, you will be on a winning path but you are limited by fuel octane. Higher octane will enable you to run higher compression ratio hence higher incylinder temperature and pressure.

Water/methanol injection will enable you to cross that octane barrier. Water reduces incylinder temperature during evaporation as well as regulating the frame speed, reducing the chance of knock. Superheated steam will also raise the cylinder pressure resulting in significant torque increase. Addition of methanol aids inlet cooling as well as lifting the octane of pump fuel.

Your highly stressed engine is well suited for this, hence I am taking a special interest on this.