This thread and its posts touches on another important question:

How much are EPA regulations on automobiles alone actually costing the typical citizen?

How much $ would be saved by the typical citizen if their vehicle's engine was optimized for fuel economy?

Another related question:

How much UP
would NOx, CO, and HC go
if all engines were optimized for fuel economy?

It might be a small percentage increase like 10% to 20%
and that might be only for NOx..

Hidden things are bad for Democracy.
This is a general principle.
( there can be exceptions for Military Security)

When you buy fuel it is hidden from you how much extra you had to buy due to the EPA.

When you buy a product or service it is hidden from you how much of the price was due to the 35% Corporate Income Tax.