Disintegrated Cat and Building a New, Quiet Exhaust
Joe Angell
I made a video showing how I built this new exhaust system, and how I discovered my destroyed catalytic converter.
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On a recent drive, I noticed a rattling sound coming from the back of the car. At first, I thought it was just a loose bolt or something similar, but it seemed to be coming from the exhaust. The most likely culprit was that one of the Car Chemistry silencers in the tail pipes had come loose.
Testing for Loose Silencers
I started by unclamping the tail pipes to remove them from the car. They should just slide out, but he clamps have crushed the pipes to the point that they had to be tapped out. I was able to use a rubber mallet on the passenger side, but the driver’s side required the 4-pound sledgehammer.
I also had to cut off a couple of braces from the driver’s side, before I could start hammering. Those were to fix a problem related to how the exhaust was hanging, but they weren’t needed anymore anyway.
Carefully removing the passenger side silencer with a rubber mallet.
The silencer itself, still firmly in the pipe.
Resorting to a sledge to remove the driver’s side pipe.
I found that both silencers were in tight. So tight, in fact, that I couldn’t get them out. I admit that I did forget that I’d riveted at least one of them into the pipe, which just might have been why I couldn’t remove them. I wound up ripping the cap off one of them, and simply crashing the other one. I wanted to upgrade the silencers anyway, and new tailpipes aren’t hard to build. That’s my excuse, anyway.
I pretty thoroughly managed this silencer trying to get it out. It wasn’t the cause of the rattle either.
Dropping the Exhaust and Checking the Cat
Since the silencers weren’t the culprit, I dropped the entire exhaust. What I found in the pipe to the collector was not what I expected. There was some kind of ceramic debris in there, almost like shavings. Tilting the exhaust resulted in a clear rattle from the driver’s side, which led me to the conclusion that the catalytic converter was ruined.
Since I was now replacing the cat, I cut it off with a chop saw and took a look. The honeycomb inside was cracked in half and freely rattled inside the housing. It probably wasn’t doing much for emissions anymore.
Dropping the muffler so that I can try to figure out where the rattle is coming from.
This debris appears to be what is left of my cat.
The honeycomb inside the cat is cracked in half, rattling around in the body.
Welding On a New Cat
I ordered a replacement cat and got to work welding it onto the car. I had to cut it down slightly due to the server space constraints for the DeLorean exhaust system. Only after I welded up the entire thing did I realize that I didn’t get it QUITE as straight as I had intended, and I had to cut my welds and do it again.
After cutting anything with the chop saw, I had to clean it up the burrs with an angle grinder (for the outside burns) and a Dremel (for the inside burrs). I feel like there should be an easier way to do the inside burrs, but this works.
Removing the outer burr with an angle grinder.
Removing the inner burr with a Dremel.
Unfortunately, I didn’t cut the cat straight and was foolish enough to weld it all the way on without a proper test fit. It was off by enough that I had to cut my new welds so I could bend it down, and then weld it back up again.
Definitely not lined up right.
I also had to cut a new elbow and weld on a new flange to mate it to the DeLorean Industries collector. I screwed up the first time and cut the elbow too short. I briefly tried a wedge of pipe to fill the game, but it really didn’t work very well.
The wedge that I tried to use to fill he gap between the flange and the blow. It didn’t really work.
For the second attempt, I added a 2.5” inner diameter pipe that would slide over both the cat and the elbow. This gave me some room to tilt the elbow and line it up with the flange properly. This time I tack-welded everything on the car before doing final welding on the bench.
The new elbow with the slide-over piece between the elbow and the cat.
Tack welding the cat on the car before doing the final welds on the bench.
The Muffler
I was about to put the exhaust back in the car when I noticed a huge gash in the side of the muffler. This is probably where the rest of the noise was coming from. It also explained the “animal fur” I found in the engine bay — it was fiberglass blown out of the muffler.
I didn’t notice this large gash in the muffler until after I welded the cat on.
“Animal fur” that is actually fiberglass blown out of the muffler.
Since I didn’t see this until everything was welded up, I had to cut off both my newly welded cat and the cat on the other side so that I could weld them to a replacement 2.5” Borla Pro XS dual in/out muffler.
I didn’t need to order new pipes from the muffler to the cat, because I already had two that I hadn’t used from The original build. These had 3-disc Car Chemistry silencers already installed in them, too.
Building New Silenced Tail Pipes
I cut new tailpipes from some 90-degree bend pipes I’d ordered for the purpose. I used the old pipes as a reference to get the length right.
Using the old tail pipe as a reference for cutting the new pipe.
I replaced the 3-disc silencers from my old build with new 4-disc ones Car Chemistry. As before, I welded on both caps to further reduce the noise levels.
Welding caps onto the new silencers to further reduce the noise.
The big addition this time was stainless steel wool between the discs. Since the exhaust gasses could push the wall through the holes in the discs, I added circles of stainless steel mesh between the wool and the silencer. It turns out a DeLorean front wheel bearing is the perfect template for cutting these circles. It took a fair bit of trimming to get everything installed, but it went fairly quickly.
The DeLorean’s front wheel bearing makes a perfect stencil for cutting the mesh.
Installing the stainless steel on top of the mesh circle.
Inserting the finished silencer into the tail pipe.
The new silencers include set screws, while the originals relied on you to either rivet or tack weld the silencers in place. I used a stepped bit on my drill press to make the holes for the screws. I used blue LockTite to reduce the chance of them vibrating out, but that might just burn out from the heat of the exhaust. I almost made sure to put the screws in the top of the pipe to further ensure that they wouldn’t fall out, but I screwed up one of them and put the hole on the wrong side, so I had to drill a new hole and weld up the old one.
Drilling the hole in pipe for the set screw. I did this before installing the silencer, of course.
To fit the tail pipes in the muffler, I needed to restore the muffler’s outlets to their original 2.5” inner diameter with a pipe expander. The old clamps had crushed them and made it difficult to insert new pipes.
Using a pipe expander to restore the muffler outlets to 2.5” inner diameter.
Test fitting the new tail pipe.
I installed some new exhaust tips to finish out the tailpipes, I used new exhaust clamps to mount them to the muffler.
Mounting the New Muffler
Before welding anything up, I had to figure out where the muffler was going to sit. The tailpipes served as a guide to get the height right. I then used two Alignment Devices (ie: blocks of wood) to make sure the muffler was far enough away from the main pulley while not being too close to the rear fascia. I then tacked on new exhaust hangers. Now the muffler would tilt from the hangers once I removed the Alignment Devices.
The Engine to Pulley Alignment Block.
Tack-welding the hanger to the muffler.
I welded up the passenger side cat first. I had to cut it down a little more to fit, but other than that it went on fairly easily.
The driver’s side was less cooperative. I again failed to cut the cat at the correct angle and had to fill the gap. If not for the fact that I’d already welded the flange to the other side, I could have just rotated everything, but now I was stuck.
My solution was to reuse the wedge I had cut for the flange elbow, before I just cut a new elbow. It fit perfectly.
While this worked, it’s not exactly pretty. There’s a kink in the pipe where the wedge filled the gap. It works fine — it’s just a bit ugly.
It’s not the prettiest welding job, but it works.
Heat Shield
Neither the stock heat shield nor the DeLorean Industries one would mount to my new exhaust, so I reused my Heat Shield Products Muffler Wrap from my old exhaust. This serves the same purpose, redirecting the heat away from the engine and back towards the muffler. I bought some new 30” stainless steel zip ties to secure it. Rather than using pliers, this time I used a proper stainless steel zip tie tool.
Clamping the warp to the muffler with metal zip ties.
Results
This new muffler is a lot quieter than the old one. For one, it doesn’t have a large gash in it and the cat isn’t rattling around anymore. But with four silencers — two stuffed with stainless steel wool — the car is far quieter. It’s not exactly quiet, but it’s not obnoxious or even all that loud. I don’t have to turn the radio up as much, and I can have a conversation at low-to-medium speeds.
At high speeds, I think road noise is where all the noise is coming from, as I can barely hear the engine over it unless I’m actively accelerating. However, the last of the low-frequency droning is gone, and I can comfortably drive for hours.
I’d say it’s around the same noise level as a stock exhaust, while also being less restrictive — while I have silencers plugged with wool in the pipes, I don’t have the crossover anymore, nor the old manifolds. Not that I’ve done any kind of performance testing on it or anything, but I am quite happy with it.