You’ve made the decision between short and long pipes for your preferred exhaust system, chosen which finish you want, and now you’ve come to picking out which size diameter your headers will be. The biggest header is the most “free flowing” so it’ll offer the best performance, right? It’s not that simple.
There are several options for diameter size of your aftermarket headers, but the two most common are 1-3/4” and 1-7/8”. Before choosing which, you must understand the basics of header sizing. A head pipe with a smaller diameter will offer a higher velocity of exhaust flow. This is typically optimal for relatively-stock builds or for low-to-mid RPM performance. Larger pipes, on the other hand, will allow a larger flow capacity, but at a lower velocity. That said, drivers with fire-breathing builds needing to pump out as much exhaust as possible choose this design, or those looking to maximize top-end power.
Headers with a 1-3/4” diameter are the most common among enthusiasts using their Challenger for daily driving—and for good reason. Likely, these cars aren’t fully equipped with internal modifications, so there’s no need for a massive amount of flow capacity. In fact, the higher velocity flow associated with the 1-3/4” pipe will offer more performance at city-driving RPM—say under 4,000 RPM.
On the contrary, 1-7/8” headers are perfect for those looking for outright speed. The lower flow rate and higher flow volume will benefit a Challenger in the high RPM range. This larger diameter will also suit builds with internal engine modifications that pump out high horsepower. A smaller diameter will cut off flow and rob the car of power.