Using your thermo co-efficient as the multiple (.89), it's probably closer to a 3.8L n/a motor (assuming an 85% V.E for that engine- could be less or more though, of course).
There are just too many variables- look at an F430: 4.3 litre, 490hp, and meets Euro IV emission standards. You could have won an F1 GP with that less than 40 years ago.