[malibuguy]

It all depends on driving habits. If your driving the car so lightly...then exhaust mods will typically not benifit. Now say if your really running the vehicle hard...say a gas truck towing alot...then yes the added flow area of a proper custom exhaust can result in better FE.

I lose about 2-3 mpg on my Yaris with my full custom exhaust...stock is a perfect 1.75" mandrel bent exhaust with a calibrated spring loaded valve in the muffler. When im hypermiling i dont go past 2500rpm. However my 2" mandrel bent exhaust does make a major HP improvement on the top end