Living in Maryland forces me to at least try and maintain an emissions compliant car. I realize there's a lot of mods that can be done without adversely affecting the emissions output of the vehicle. Assuming everything is in good working order, what types of mods really affect the emissions levels a vehicle is putting out ? For instance, would increasing the displacement (as long as it's within the limits of the intake/exhaust systems capacities) necessarily cause anything to go amuck ? I'm just looking for some generalized guidelines on things that stretch a car's abilities to reduce emissions. Thanks!

Kyle

 

but, to make the engine run right (even at idle), you have to provide more fuel, that in an of itself will require cause increases of emission. Other changes that factor in are increased compression (raises NOX readings), advanced timing (same thing) and longer cam durations (CO readings).

Increasing the capability of the engine to flow more air (by using headers and some headwork) can often pass testing without problems.