Heres a thought on passing emission test

[Power Hungry]

One thing about drive cycles and relearn procedures is that they handle a relatively specific set of driving conditions... Mainly "closed loop" light to mid throttle fuel curves. Open loop fuel, timing curves, camshaft curves, shifting (points, not pressure), torque management and other functions are not controlled by the relearn procedures. Timing is controlled by knock sensors, but that's another story.

Much of the perceptible performance gains under hard acceleration come from timing curve and open loop fuel curve adjustments. Much of the fuel economy gains come from timing curve adjustments and changes to shifting strategies. At cruise, there is little fuel change outside of correcting for CAI discrepancies. This is why we can make more power and still be able to pass emissions test with ease. Modest timing curve adjustments can lead to reasonable improvements in fuel economy, but it also weighs heavily on fuel quality and octane. I have seen as much as a 2-3 MPG difference in fuel economy depending on which brand of gas I run or which station I fill up from. Performance difference is negligible though, at least for the old butt-dyno. The Expy always runs like a scalded dog.

Now... don't ya feel smarter?