In the world of high-flow exhausts, size really does matter. Not just for the sights and sounds—the components have to fit together in order to work. While you might know your ride’s horsepower off the top of your head, most of us just scratch our heads when it comes to exhaust diameters. Fortunately, sizing up your system is easier than you think. Check out this quick guide for straightforward advice on figuring out what kind of pipes you’re packing.
Outside Diameter vs. Internal Diameter
There are two types of measurements to pay attention to when you’re working with tubing: the external diameter and the internal diameter. The external diameter is the distance from edge-to-edge including the thickness of the tube itself. The internal diameter is the distance from edge-to-edge not including the tube thickness—so just the space inside.
- Most exhaust tips and mufflers use an internal diameter measurement because they usually slip over the exhaust pipe
- Most exhaust piping uses an external diameter measurement because it fits inside a muffler or tip
How to Measure Outside Diameter
- If the end of the pipe is fully exposed (not covered by an exhaust tip or fitted into a muffler), use a tape measure or ruler to measure from one outside edge to the opposite outside edge across the center point
- If the end of the pipe is blocked, use a pair of dial calipers to measure the distance
- If the end of the pipe is blocked and you do not have a pair of dial calipers, you can use a bit of arithmetic instead. First, find the circumference of the pipe using a tailor’s measuring tape (or a piece of string that you can then measure with a standard measuring tape or ruler). Then, divide the circumference by pi (3.14) to get the outside diameter
How to Measure Internal Diameter
- If the end of the pipe is exposed, use a tape measure or ruler to measure the distance from the inside edge to the opposite inside edge through the center point. For a more precise measurement, use a pair of dial calipers.
- If the end of the pipe is not exposed, you’ll have to cut the pipe to take a proper measurement
Inlet vs. Outlet
Exhaust fumes flow in one direction—from your engine back to the tailpipe. Some exhaust systems use different diameter tubing at different points along the path. For example, the tubing between the exhaust manifold and muffler might start at 2.5”, but then it might switch to 3” for the tailpipe. When you’re taking your measurements, make sure to check both the inlet sizes (the section pointing towards your engine) and outlet sizes (the section pointing towards your tailpipe).
How to Connect Exhaust Components
When one section of pipe fits inside another section, it creates a lap joint. You can use a band clamp or U-bolt to secure the connection or you can weld the joint for a leak-free fit. Many exhaust tips have band clamps built right in, but you can always weld for extra security.
When two sections of pipe are the same outside diameter, they create a butt joint. Band clamps and welding are the only options for making a secure connection.
Remember, if you ever have any questions about finding an exhaust component that fits, we have answers. Give us a call at 800-874-8888. Our expert pit crew is here to help you find the right gear for you ride.