Or you can increase the compression ratio, right? But then you need to run higher octane fuel to avoid detonation. Still though, at the end of the day you have a higher horsepower engine, and in theory also have better fuel economy, because you can drive at lower RPM's to achieve the same horsepower rating.. umm right?

 

So if i get an O/R X pipe and a nice tune I can see 45MPG in my car????? but would be in trouble if they even did an emissions test on me? (Ky does not require annual checks etc)

 

No, it has good emissions. That car along with a couple others are a good example showing that cars can be built to have very good fuel economy & power without going hybrid, granted they had to modify the engine quite a bit to achieve that.
catalytic converters do help, but they don't fix it. Quite a few people have used a tune alone with no converters & passed emissions, but those tunes aren't with power in mind.

If you have a way of tuning the car, yes. The amount it will go up will depend on how your car is currently running & how lean you can run it without issue. Tuning a friends car .2 lower than surging point resulted in a 4mpg increase for him. Make sure you only do it to your cruising conditions, running leaner will cause it to burn hotter which isn't an issue when there isn't much air/fuel in the cylinder, at wot or heavy load it can cause lots of damage. Running rich under those conditions help keep temperatures down to avoid damage. I personally try to aim for around 12.9-13.1 at wot if n/a 11.9-12.1 at wot if forced induction & lean it out as much as possible at cruising rpm/load until it starts to surge then back it off a few points. (which in most cars is anywhere from 16-17)
That all depends on your engine setup. If you're getting away from how much the engine will take in in a given time there are multiple routes you could go to increase power & fuel economy. The idea behind most is moving where the engine is most efficient to a lower rpm, then making up for it in different areas. I have an 8:1 compression ratio in my ranger & can get away with 25psi on pump, raising my compression would significantly lower the boost I could run or hurt my timing whereas just adjusting it to run leaner would help my fuel economy without hurting power. In some situations, higher compression may be a good option. There are quite a few crazy ideas out there for it; there was a company a while back putting notches in the combustion chamber to raise turbulence which by their testing helped quite a bit & the customers they had seemed very happy with the results. One of the guys there was playing with modifying his cam to make his engine more like a miller cycle engine where the intake valve stayed open partially during the compression stroke to have a lower compression ratio with a high expansion ratio. It's increased economy at the cost of power. I'm unaware whether he finished it or not, that's been a few years ago.

You would fail & you would have to fix it then take it again (at least that's how it is in most states) There's no testing where I live.

 

no testing here either.