New Exhaust = Worse Mileage?

If you can remember what the old exhaust looked like, and look at the new pipes in comparison. It’s most likely made of crush bent pipes. I’ve seen some crush bends that were made pretty severely restrictive. I’ve also seen some really goofy things like for example going from a 2.5” cat outlet to a 2” pipe the rest of the way back and just filling the gap with a porcupine mass of weld and weld wires sticking out.

I used to make exhaust systems and only used mandrel bent pieces. Even simply replacing some of the rusted out pieces, people would experience better mileage and better power. If your old exhaust had better bends or larger diameter pipes, that could be the cause.

Replacing exhaust on Toyota’s is usually simple because they bolt in. That’s why Toyota’s are common victims of catalytic converter theft.