I will not argue that EGR can't reduce knock in an engine, it clearly does that, but it does so at the expense of efficiency. The whole point of increasing compression is to bring the oxygen and fuel molecules closer together to insure more of them light and burn during the power stroke, adding non combustible gasses to the mix again spaces those molecules farther apart and they take longer to burn (after the power stroke is complete) and less of them will burn because they are not next to each other. What would be the point of raising compression if you then have to dilute the mix and keep it from burning as completely? Also since you are pumping more gas mass (actual gas not gasoline) through the engine it is wasting more energy through pumping loss. I have done a bunch of experimenting with and without EGR and have lost MPG every single time and can not fathom it not costing HP either.