The "lumps" will be beneficial thru out the entire RPM range of the engine. They will greatly enhance the throttle response at lower RPM, and make the engine operate more efficiently. They possibly could improve MPG because they also create a higher velocity of air/fuel mix thru the bowl into the cylinder causing more complete fuel burning. The premium fuel requirement is mostly a function of your compression ratio, and is not affected by having or not having "lumps" installed in the cylinder head. Feel like I just did an Infomercial(LOL)!
