Due to the change in the MAF housing the computer "thinks" the car is getting LESS air then it really is... We know that the MMR will flow more air than the stock air box. But if you look a the graph you can see that the computer is reading the MAF Counts, and showing the MMR is LESS than STOCK... As a result the computer supplies LESS fuel... even thought there is MORE air... This causes the engine to run leaner... this give you the power gain... but it is by running leaner....