Coming from a racing background, I'm VERY pleased that no matter how hard I drive my 06 HCH, i can't get WORSE that 30 MPG.
To me that is amazing, as my Indy Car is lucky to get 3 MPG.
An engine is really just a big "air-pump", and anything you can do to make the air flow easier, the more efficiency (MPG) you will get. The additional benefit is an increase in Horsepower. Both of these upgrades are simple and don't require any special adaptions or knowledge to perform. Any reliable shop can easily do them for you.
The first two upgrades that both have improved my MPG by about 5 MPG was to get rid of the highly restrictive small exhaust and run a full size exhaust directly off the OEM Cat. If you want a quiet car, this is not a good choice, but if you want the air to flow and the MPG to soar, try this.
Aero Turbine 2540i Muffler direct to OEM Cat. (no resonator)
(Keep your OEM resonator and muffler close by as your wife might make you put it back on when she hears your Hybird "Roar" into the driveway though)
The other side of this MPG upgrade is how cleanly and powerfully you can get the air IN your engine. Several intake packages may work, but I know that the following quality intake was a simple bolt-in project for my 06 Hybrid.
Fujita F5 Short Air Ram Intake SR-1923
AND - with all the extra power, you won't have to look at the ugly butt of the Prius any more - because they will all be behind you.
