Where do you draw the line?

[dkjones96]

This is really because of another post I saw:

Originally Posted by maxxgraphix

Disconnect the EGR. Get a high flow CAT and muffler.

The EGR actually won't even increase mileage when disconnected and if it was working properly this will decrease mileage, FYI, but getting a high-flow cat (or none at all) will leave more pollutants in the exhaust and will pollute more than if the car in question leaves it on and suffers a bit of economy loss.

I guess it really depends on what your mods are for, pure MPG or more earth friendly. While you might think those are synonymous, they aren't, and I'm just wondering where people start to say 'This will give me better mileage, but will pollute more'.

I tend to leave my mods to ones that will pollute less and/or the same while increasing mileage. The mods I do to my car most of the time don't even use new parts, they are off junkyard cars so I'm not paying a company to pollute making me a new electric fan assembly when an automaker already has for the used one that might end up thrown away needlessly if I don't use it.