Mar 13, 2008 update to the BMW 325is project car

Spec Exhaust Excitement

Judging the cut location for the downpipe was easy with the the Spec E30 exhaust next to it; we used the hanging bolt location as our index.
A large fiberglass cutting wheel made short work of the downpipe tubes; you can see the first cuts at the bottom. We did have to use a reciprocating saw to get the remaining metal that the cutting wheel couldn’t reach.
We used a Dremel with a sanding drum to give the tubes a bit of taper at the lip. Then we rubbed some motor oil around the edge to help the downpipe tubes slip into the Spec E30 exhaust flange.
With some help from a bench vise, we were able to line up the downpipe tubes with the Spec E30 exhaust flanges and slide the assembly together. We then snugged down the clamps that were provided with the exhaust.
We’re eager to hook up our Innovate Motorsports wideband air/fuel gauge, so Tech Editor Per gave his welder a bit of a break from the Saab 99 to help us attach the O2 sensor bung.
The bung has a small plug for when the O2 sensor isn’t plugged in, but we’ll get that installed before we take it to the dyno.

Our friend Rennie at Redline BMW came through for us with a replacement downpipe, so we were able to finish up the Spec E30 exhaust install this weekend. The trickiest part of the operation was fitting the two downpipe tubes into the Spec E30 exhaust’s flanges. In a nutshell, we figured out where to cut the tubes, used a fiberglass cutting wheel to slice through the metal without deforming it, Dremeled away some material from the outer edge to make fitment easier, and then slid the downpipe tubes into the exhaust flanges with a dash of good ol’ 5W30 motor oil to facilitate things.

Once we had the BMW downpipe securely fastened to the first of the three parts of the Spec E30 exhaust, we mocked up the fit and then took the pipe assembly over to Per so he could weld in an O2 bung for our upcoming Innovate Motorsports air/fuel monitor installation.

Bolting the downpipe to the exhaust headers is a bit of a pain; we used plenty of weird extensions, angle drivers, air-driven impact wrenches and manual gear wrenches in the process. The middle and rear segments slipped together with ease by comparison. Ours is a very early version of the exhaust, so it only had one rear hanger for the rubber doughnuts in the back. Apparently the newer versions use dual hangers and forgo the middle-section hanger, so we might weld on a bar of steel to mimic the newer style.

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