The Right Angles

The Right Angles

Today’s blog post title almost sounds like the next big nerd-rock band. However, we’ll be discussing music of a different sort on the blog today.

That music comes to us by the way of a custom exhaust setup that we’re building for a customer’s V12-equipped Mercedes-Benz SL600. You may have seen the earlier posts, in which we fabricated the header merges, part of the midpipe and the hangers for the rear mufflers. Now it’s time to deal with the middle. As we discussed last time, when cutting a Y-pipe, the single-exit side is always in an oval shape. So, in order to return to the standard cylindrical configuration, we have to attach a transition that changes shape from oval to circle. And that’s exactly what we’ve tacked on below:


With the transition in place, we started running the last part of the midsection. As the customer is requesting a custom sound with oodles of civility (he won’t be the primary driver of the vehicle), we’ll be incorporating yet another pass-through resonator just before the rear axle. It’s at a bit of an angle to fit underneath the car’s body, so now we have to fashion ourselves a bit of a pie-cut to run to the front end of that next pass-through resonator.


As with all our exhaust work, there’s plenty more measuring than there is cutting. After fitment is where we want it, we’ll remove the tape, clean the pipe and tack it all together. It’s a stronger hold than the tape, but still removable with a small cutting wheel if we really need to adjust something.


However, fitment is all good with the already-tacked parts of the midsection, so now it’s time to focus on the transition from the final pass-through resonator to the mufflers tucked under the rear bumper. This is going to be an extremely tricky cut, as we have several things we need to accomplish:

• The exhaust needs to snake through an opening in the suspension components that only a circular pipe can fit through.
• The exhaust must then bend upwards and to the right in order to meet the Y-pipe that will send the exhaust gas through the final pair of mufflers.
• The exhaust must ALSO transition from a circular shape to an oval before connecting to that Y-pipe.

Tricky indeed. It needs to change shape and angle all at the same time. After some thought, we came upon a solution that will meet all our criteria without cutting down on exhaust flow with extremely restrictive bend angles. It’s time to make some (again, oddly complicated) pie cuts!


Essentially, we’ve cut a piece of oval exhaust piping into a number of small, acute-angled pieces that will comprise the bends we need to meet the Y-pipe. However, since we need to start as a circle, we’ll also be shaping each piece of the pie cut a little wider than the one after it. Seeing as how the inside area of both the oval and circular pipes are the same, therefore it stands that each oval piece can be slowly hammered out to a circular shape over the course of the transition, without losing an inch of exhaust flow. So we set about slowly widening each piece of the transition by hand, until we had a piece that changed both angle and shape simultaneously.


Now, argon backpurging is absolutely necessary with these welds. Given the sheer number of welds required in a pie-cut piece, any sort of oxidization on the inside of the bend will cause the exhaust gas to get extremely turbulent, which will cut down on both power and sound quality. Therefore, we cranked up the argon and got to welding. When we were done, we made sure everything was still in the shape we desired — which it was — and then placed it back underneath the car. Fabrication tells us that it’s easily one of the most difficult exhaust pieces that they’ve ever made, so you can imagine how happy they were when everything fit together nicely. Hard work pays off!


Seeing as how there’s a number of welds packed tightly together, we couldn’t help but give you a solid close-up shot of the welds. After all, it wouldn’t be the Fluid MotorUnion blog without a little weld porn, now would it?


There isn’t much left for Tom’s SL600 exhaust, and we still have plenty of other action taking place at the shop, so come on back to FMU’s blog tomorrow for even more excitingly fresh content! Have a great day!

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