[Mcgarry97geo]

Originally Posted by ShadeTreeMech

assuming a new air intake allows as much air into the engine as it can get, you're likely to increase compression a bit, sure.

But a higher compression ratio requires higher octane fuel, otherwise the ECU will retard the ignition and lower your MPGs.

Trust your ECu; if it's getting good info from good sensors, it's designed to get the best fuel mileage possible within the contraints of the engine design. If you trick the ECU to run leaner, you'll burn pistons, valves, your head, or all the above. Run too rich and you waste gas.

However, if you run warm air into the intake, you can sometimes improve things, all depending on the engine. Otherwise, without redesigning the engine, there's not much to be done.

Ok that clears things up. I've decided not to put one in since any gain in mpg would offset the price for replacing parts.