Do they give better gas mileage? Why/why not? After a header install, does cars usually run more rich or lean?

 

You usually get less mileage after the header install because people can't keep their foot off the gas

Theoretically you would get better gas mileage because you are making it easier for the motor to get rid of the exhaust. As far as rich or lean after headers I'm not sure........

 

I agree with FastZ theoretically you may see better milage however, I keep my boot pretty close to the carpet so my milage stayed the same.
As for rich or lean; back in the carburated days you would change the jets to fatten the mixture up a little or the engine would run lean.
My LT1 is doing fine since the O2 sensors are keeping the mixture in the right ballpark.

Mike

 

I didn't notice a difference.

 

anyone have some highway numbers with the cruise set? thats the only solid method to tell the difference IMO.