Butterfly Valve Modification
 

I recently found this on a truck site and was wondering if anyone here has had any experience with trying this out. The GMC 4.3L engine throttle body butterfly valve has a curved "lip" called a diffuser on the downward leading edge. The mod I read about was to cut the diffuser off so that the valve was flat. The effect was to increase power by letting in more air sooner. And increase fuel economy by keeping a very light foot on the gas pedal. Any thoughts or experience?

How hard you press the pedal has no bearing on fuel economy. If you allow more air in the engine with less pedal pressure, the O2 sensor will just tell the computer to add more fuel. I'd be very skeptical. Think about it. If GM could get more power and better economy from such a simple modification to the design, don't you think they would have made it that way from the factory?

I could see more power but am having trouble with the better fuel economy.

also realize that the engine will be louder. A big reason that an intake or throttle body modification isn't done by the factory is for the noise. Many factory intakes have built in "Mufflers" so that the intake isn't that loud. John Q Public doesn't like noisy cars and that is who the car manufacturers cater to.

I scare my step-daughter when my car gets above 4,000 rpms because it is loud and I "MUST BE SPEEDING". A free(er) flowing car is by definition louder.

There is a modification on my yaris where you swap out a throttle body with that of the corolla (larger openning) and it gives it about 2-3hp but there again, louder.

Jay is right. Since invention of oxygen sensor, formula is very simple:
more oxygen=O2 picks up engine running lean=ECM corrects by pumping more petrol in.
You simply can not bypass that. The only thing you can do is to use aftermarket chip that fools either O2 sensor or ECM that mixture is not lean. But then what good will it do, running lean all the time? Eventually, you'll damage something and costs will over weigh what little gas you saved.

From years of experience with frugal driving, I know ONE thing that WORKS well. CHANGE YOUR DRIVING STYLE. Get a MPG displaying device of some sort "in your face", I am aware of some that even work with cell phones. THAT will be what is called a "habit modifier", as you start chasing better mpg. Soon enough, new habit develops.
Good example would have been my son. He has MAzdaspeed, which is a turboed sports car. He drove with Scangauge connected for several months, and managed to establish solid 36mpg on a car that is rated for 28 at the best.