I have read what you guys say about the boring of the throttle body to 60mm how much performance does it add? what does it doe for fuel economy?

 

Well, what happens is the motor takes in more air, the o2 sensor reads leaner than normal and compensates by adding more fuel. This in turn lowers your overall MPG. Don't think about it as just adding more air because the computer will automatically compensate for it all the way to it's highest map setting or threshold.

 

Any idea on the performance gains?

 

My fuel economy stayed virtually the same .. As long as you are not running it wide open all the time ...
I bored the TB and port matched the upper /lower plenum and extrudehoned the plenum at the same time added around 12HP from the previous dyno reading