Project SR E30: Part 8 – Fabricating a Custom Stainless Steel Oval Exhaust

Part 8??? Wow, we are getting close to the end now! Can we make it a 10 part series? 

If we had to pick one thing on this car that we are most proud of it would have to be the exhaust. It truly is just a work of art. We really outdid ourselves on this one.

So you may be asking, why did we go through the trouble of fabricating an oval exhaust? It’s quite simple actually. We were forced to by chassis constraints.

BMW engines have the exhaust outlet on the right side of the car. Nissan engines have the exhaust outlet on the left side of the car. This means that the E30 chassis has provisions (a raised floor section) to run an exhaust on the right side of the car, but not the left. If we were to make a round exhaust, it would end up protruding 3″ past the frame rails and scrape on every bump on the road. If we didn’t go with oval pipe, we would be stuck with awful ground clearance.

Full disclaimer: this is my first time TIG welding. I actually bought a TIG welder specifically for this project. I spent about a month practicing before finally diving into the exhaust.

Stainless Oval Mandrel Bent Exhaust Pipe
We bought some really cheap 3″ stainless oval piping on the internet. We made sure to buy it in mandrel bends so that we wouldn’t have to pie-cut the entire exhaust. We also made sure to get two 3″ round to oval adapters to allow us to mate our exhaust to the turbo elbow, and so that we can add a muffler.
BMW E30 SR20DET Turbo Elbow
Our first challenge was to make the downpipe section that connects to the turbo elbow. We ran into a lot of issues here after discovering that the Nissan turbo elbow only works with a 2.5″ 3 bolt flange. It is not possible to mate a 3″ pipe directly to the turbo elbow. Having not accounted for this, we were in trouble.
RB25 Downpipe Modified to fit an SR20 swapped BMW E30
What is this monstrosity you might ask? This is a mutilated RB25 downpipe. We found it digging through our junk drawers and realized it had a 2.5″ flange with a 2.5″ pipe that quickly steps up to a 3″ pipe. This allows us to add our 3″ round to oval adapter at the bottom.
SR20DET BMW E30 Downpipe
We had to add a pie cut to make the downpipe fit. Unfortunately, the way this downpipe happens to be constructed, it actually adapts the 2.5″ pipe to an oversized 3″ which is then slipped over the actual 3″ mandrel bend and welded in. This sucks for us because that is the exact spot where we need to place the pie cut. This means that one side we are forced to fill a huge gap, and on the other side, we have to weld to two layers of pipe that are welded together. It’s a very odd weld, and it won’t look pretty. Lots of filler required.

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