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How to Build a Through-Frame Exhaust System
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How to Build a Through-Frame Exhaust System

Views:3     Author:Site Editor     Publish Time: 2019-03-18      Origin:Site

Exhaust design is often a tricky process. You want to keep the pipes as close to the body as possible for maximum ground clearance, but there are so many obstacles in the way that often force you to go underneath the frame, and you end up dragging your mufflers or header collectors across every speed bump. If you have an X-frame chassis, used in just about every car from the 1930s to 1960s, then you have even fewer options—unless, of course, you go throughthe frame.

Many early X-frame cars had a single exhaust that was channeled through the chassis, like this 1941 Lincoln Continental featured here. The original exhaust went through the driver side of the frame but only had a 1.5-inch diameter, so it wouldn’t exactly work for a modern, high-flow exhaust system that could support a 6.0-liter V8. For this setup, you need to cut and channel the exhaust on both sides in order to get all those gasses out from under the vehicle.

Going through the frame is fairly simple- you basically just cut a hole, but we are not building a daily driver. This is a high-end show-and-go vehicle, so the underside needs to look just as good as the top side. To clean up the pass-through areas, we used some 3-inch steel tubing and 3/16-inch plate steel to close up the holes in the frame around the exhaust. The framerails are just large enough to accommodate the tubing without sacrificing any strength, and we are boxing it all in, to add a little strength.

This is a more complicated exhaust design not only because of the frame, but also because it is 100-pefcent custom. You can’t just order up a pre-fab kit with all the right bends in all the right places. Sure, you could take it to the local muffler shop, where they would bend mild-steel tube, but those are not mandrel bends, so they get kinked and stretched, which doesn’t look good, and more importantly, they don’t flow as well. To simplify the building process, we ordered a 2.5-inch, stainless-steel builder’s kit from Magnaflow. The kit provides a bunch of different mandrel bends and long tubes, so we can “stick build” our entire exhaust system. That means we cut and weld most of the bends to fit the chassis.

All of the tubing in the Magnaflow kit is slip-fit, so you have some options on how you put it all together. The majority of the system was welded together, with the exception of the mufflers, which we clamped together with the supplied slip-on sealing clamps for easier replacement down the road. The tailpipe sections were also slip-clamped, and the front connections utilize a pair of stainless-steel flex joints with V-band clamps that will be attached to the downpipes coming off the engine. Using this kit made the entire process much easier than trying to guess what bends you might need for piece-meal ordering.

The bulk of the work on this project was routing the pipes through the rear suspension. We had to move in toward the center of the vehicle, up and over the rear axle, and back out to the tailpipe exit (which is through the body), without interfering with the suspension operation and servicing. For such a large chassis, there is not much room for routing tubing.

This project requires several tools, including a MIG (or TIG) welder, a bandsaw, and the standard hand tools. You can get away with a chop saw, but you will run into a complicated cut that will require you to V-cut pipe to facilitate an increase in bend radius, or cut in the middle of a bend, which is more difficult to do on a standard chop saw. Even a handheld bandsaw can do the job, if you clamp the tubing well and have a helper to assist in cutting straight. An inexpensive, used hobby-quality bandsaw with a fine-tooth blade (14-24 TPI is best) can be found for around $100. They are worth their weight in gold.

We spent a couple of days laying out the exhaust and modifying the frame, then a couple more days laying out the rest of the exhaust system. When we finished welding it all up, each section was wrapped with DEI exhaust wrap. This was done to help keep the heat in the exhaust so it doesn’t transfer into the cabin of the vehicle, and to help quiet any potential rattles where the tubing passes through the frame. The tubing is all secured so that it does not move; the flex joints at the front of the system absorb most of the engine’s vibrations, but it is still a moving vehicle, so the wrap will help stifle any errant rattles. We also wrapped the mufflers because they are so close to the floor pans.


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