2000 Boxster Exhaust Mount failure

[911monty]

Yeah I saw the Wevo's mentioned and was thinking along that line but was first wanting to eliminate possible binding in the system. If you can take some high resolution Macro photos of the bolt failure point and post them for analysis. Tension, shear and hysteresis fractures have some very obvious failure images.

[911monty]

I have some additional thoughts on this and will explain in basics for thought and the collective input.
As earlier stated the engine, trans and exhaust are designed as a unit or structure. This structure is suspended on elastomeric mounts to isolate vibration (harmonics) from the vehicle body and the driver. You have probably noticed an increase in vibration to yourself and I suspect your mirrors after the WEVOs were installed. The engine package however was designed to deal with these harmonics. Rotating equipment creates harmonics, Most engines deal with these crank harmonics with a viscous or elastomeric damper mounted on the crankshaft end called the harmonic damper. Porsche uses the dual mass flywheel to control these harmonics. An interesting thing about harmonic vibration is that you can beef up one point i.e. the Wevo mounts, but the harmonics are transferred to some other point, such as your exhaust bolts. The harmonics to fatigue metal at the rate you seem to be experiencing would have to be in the order of >16k Hz. This should create some rather uncomfortable buzzing in your car. My question to you is by any chance are you running a LW flywheel?

[Pbastian]

I agree with you, now, after I have learned all this over the course of several weeks. I won't have any pics of the failed bolts at the moment, but I have a few things to add to this conversation. Technically, the jury is still out, because I don't have the car back, and won't find out for some time if those bolts will fail again. But, the shop where the car is now to be repaired said that the failed bolts were welded into their carrier, which is a mistake made by the previous mechanic. I think the stock installation had the bolts loose in the carrier. The carrier itself is welded to the muffler, but the bolts are just encapsulated in the carrier, and loose, and then connected to the upper mounting bracket. So, if the bolts were welded to their carrier on top of the muffler, then I can easily see where this would create issues, perhaps even with the Wevo's in place. Still, because of the "balance" created by the original engineering design, I am going back to that. Stock trans mounts are going in, Wevo's are coming out and muffler is being repaired and reinstalled.

We shall see...