“Measure twice, cut once.”

It’s some of dad’s greatest advice, and it certainly applies to assembling a custom exhaust system and components. Here’s another great piece of advice for building an exhaust system: Watch the video below.

Our Summit Racing Quick Flicks video covers the basics of choosing the right exhaust pipe diameter, including

  • Difference between inside diameter (I.D.) and outside diameter (O.D.)
  • Exhaust clamps and connectors
  • Exhaust connection tools

Some of our favorite and most creative swear word combinations have been crafted over a set of mismatched exhaust tubing. Keep your exhaust installation (and language) clean—watch our video now!


Hi. I’m Mike, and on this installment of Summit Racing Quick Flicks we are going to discuss exhaust pipe sizing.

When building a custom exhaust system out of miscellaneous components, it is important to understand how the industry sizes different components that are going to be necessary to build that system. Exhaust piping, mufflers, collector reducers all are going to be sized differently from one another to ensure compatibility and to make sure they mate up with one another.

What we are going to discuss is the difference between the measurement of these items when it comes to OD in comparison to ID and what components are going to go ahead and fit together with one another as an end result.

The first component we are going to discuss in building one of these systems is exhaust piping. Most exhaust piping is going to be measured using OD dimensions which is outer dimensions of the pipe or the outer diameter. That means if you were to purchase a three-inch pipe—let’s say like the one we have here—the outside diameter of this pipe would actually be three inches. This creates a situation where this pipe is designed to be a slip fit or slip into a component that has a three-inch inner diameter.

That will essentially create what is known as a lap joint between those two components where one fits within the other component. This is important to understand because sometimes you have to connect one pipe to another, say from a collector reducer over to the pipe itself. This creates a situation now where the two items cannot actually be slipped in one another and it makes it not possible to have that lap joint like we mentioned. This is known as a butt joint. Exhaust system components such as mufflers and exhaust tips normally use inner-diameter dimensions on the piping used to build these components. Most of the time, this does create a lap joint fit when it comes to connecting this pipes to these components in the system.

The most common type of connection when connecting a piece of exhaust piping to a component such as a muffler is what is commonly known as a lap joint connection, which essentially means that we are going to be able to insert the pipe into the component as shown here.

This type of connection is probably easiest to deal with as well because you can typically take a standard saddle clamp or the proper band clamp and get these two connected to one another, or you can just weld the seam between the two for a leak-free fit. These will always have some measurable leakage though if using a clamp to connect the two, because what will happen is you will always have that seam between the two components that is going to give it the ability to have just a small amount of leakage between the two.

The other type of connection used in a system is what is known as a butt joint meaning that both components are going to have the same outer dimensions as one another. Exhaust piping is a common area where you are going to encounter this. This means that when you try to go connect the two pieces you will notice that if gives you a seamless fit but at the same time you are going to have trouble getting the two components connected to one another without the proper clamp or being able to weld the two components together. This can prove to be difficult for the do-it-yourselfer who doesn’t own a welder, is at home in their own garage trying to build a system independently of buying a preformed system specific to their vehicle. Here at Summit Racing, we carry a couple different clamp designs that are going to be used depending on the type of joint you are trying to connect together.

The first two we are going to be focused on are lap joint connection clamps, first being the saddle clamp which we are probably most used to seeing. This clamp here is going to use a U-shaped bolt essentially and a saddle bottom which is basically going to crimp the two pieces of pipe together to create the seal. We do have another option though which is what is known as a band clamp, and a lap joint band clamp is going to be evident because you are going to notice that one side is going to be visibly larger than the other. It’s literally going to taper, meaning that you have one pipe that is going to be fitting on the inside of another. These do not clamp as much as they hold the two pipes stationary and create a full 100-percent seal via this seam internally here. These are the more desirable of the two clamp designs because you don’t get any distortion of the pipe when they are connected together.

In comparison, when connecting a butt joint connection, your only option in the clamp world is going to be to use a band clamp—the reason being is that a saddle clamp will not have enough meat to connect the two with a saddle clamp design.

If you look at the difference between the two-band clamps out there, you will notice that the lap joint has the tapered end on it whereas the band clap used to connect the butt joint. It’s going to be the same diameter throughout. There is no tapered edge. It’s the same internal diameter. This is a good solid way to connect the butt joint, but the best way to connect the butt joint is via welding.

 There is a way also to go ahead and convert your butt joint over to a lap band joint. We sell this tool here at Summit Racing Equipment. This is a tubing expander that is basically going to go ahead and create the extra clearance internally inside the tube to make it so that whatever component you’re trying to connect will now slip into the component you are expanding. This is a good option if you want to go ahead and use the saddle clamps as an end result to build your system. 

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Author: David Fuller

David Fuller is OnAllCylinders' managing editor. During his 20-year career in the auto industry, he has covered a variety of races, shows, and industry events and has authored articles for multiple magazines. He has also partnered with mainstream and trade publications on a wide range of editorial projects. In 2012, he helped establish OnAllCylinders, where he enjoys covering all facets of hot rodding and racing.