...reverting exhaust gases at cruising speeds? I have a v8 engine that got better mileage at highway speeds with a radical cam than the street version. Is this because of the reversion causing the engine to burn less fuel? This engine is EFI and is tuned lean for cruising. I know the common thought is that more vacuum equals mileage at cruise speeds, but this increases pumping losses; plus the exhaust reversion would essentially make the cylinders smaller. Am I right in my assumption? Please help me out here.