Exhaust decision

On the sort of side tracked rallycross E 21 build. I drove it in to work yesterday and was thinking about how I wanted to run the exhaust. Of course there's a hole list of other things that need done before I get to the exhaust but I'd like to get a parts list together so I can start pricing things out.

The stock exhaust is nice and tucked up under there however it's heavy and leaving some much needed power on the table. So far I'm thinking header, high flow cat and a glass pack which leaves me with routing.

The stock system twists and turns up through the rear suspension with very little room to spare. Ideally I'd like a side but that creates a couple issues.

Ground clearance, I'd like to use oval tubing. But where I would have to route it is directly under the gas tanks. I'd be concerned about heating up the fuel and because it would be the lowest point of the undercarriage catching on something and getting ripped off or shoved up into the fuel tanks.

Or I could just run it straight back with a turndown before it gets to the rear axle. But with a gutted interior it will be really boomy on the inside.

Which way would you go?

I would do everything in my power to keep stock routing. Side exits look hack on street cars that were not built for them and are clearance issue as noted.

By the time you buy oval tubing to build something, you could probably source a nice full exhaust using round tubing.

Stock routing with a turbo type muffler (ansa, hooker, magnaflow, etc), header and high flow cat.

as the E21 has an IRS suspension.. why not just route the oval tubing below/next the diff and out the back of the car?

That said, BMW is -very- good at designing exhaust systems. I am not sure about the E21, but the later models do not leave much on the table in the way of power.. they are very heavy though

93gsxturbo wrote: I would do everything in my power to keep stock routing. Side exits look hack on street cars that were not built for them and are clearance issue as noted. By the time you buy oval tubing to build something, you could probably source a nice full exhaust using round tubing.

This. I had a side exit exhaust on the Dart for a while, and the ground clearance issue was a PITA. Didn't help that I had not come up with adequate support for the part sticking out the side, and sometimes it would vibrate its way a couple inches down and have to be pushed back up.

Ok points taken. I don't know the numbers off the top of my head but even a couple hp on top of the hundred it makes now will be very noticeable.

A guy in the E21 community developed an exhaust for his autocross car. Very nice system that has tested to perform as well as the much more expensive ones that are on the market. He made a deal with a vendor who sells them for him. If I keep the stock routing I'll likely go with this system.

Are there any pictures of under the E21? I like side my side exhaust on my nissan but don't want to be talking out of my blow hole and recommend it without seeing what your dealing with.

I used round tubing until the final foot or two, then I merged the 3in into two 2in bits of tube to get under the pinch weld/ rocker. No clearance issues with this yet.

It's very flat , the floor pan is the lowest point of the undercarriage once you get to the rear of the front cross member which is only about an inch lower.