Question: what is the difference between 1 7/8 and 1 3/4 headers?
Answer: The main difference between 1-3/4” and 1-7/8” headers is one-eighth of an inch. That doesn't sound like much at all, however, a Mustang's engine will notice the difference. Too large of a diameter can have a negative impact on engine performance. ... A larger diameter header can evacuate more exhaust.