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Last week my ZZP catted downpipe decided to part ways with its flex pipe during a track day, ending my day early. This is my 3rd downpipe I've now blown apart. I was wondering what other folk's experiences are with this? I'll give a little more detail. My factory pipe was removed at around 25k miles and I installed a used Hahn catted DP I purchased from a member here. I ran that pipe for about 10k miles on the stock tune. Then I tuned my car, 22psi trifecta tune (see sig for bolt on list), and ran ~30 runs at the drag strip and somewhere around 7 track days and 70k miles when it blew a hole in the flex pipe. I swapped the factory DP back on while determining how I was going to replace it. During that short time I blew a hole in the flex pipe on that one as well. So I decided to get the ZZP unit. That has seen another 5 or 6 track days and 35k miles before catastrophically failing by separating the flex pipe from the rest of the pipe and dragging it (causing the hot muffler tip to melt through my bumper).
Here's what's left of the ZZP pipe:
I don't have a picture of the flex pipe yet as I haven't been able to get my car in the driveway because of construction around my house. Here's a couple of pictures of the factory pipe and Hahn pipe both damaged:
I was wondering, is it possible there is extra load on the flexpipe because it's pretty much holding up the entire weight of the cat and mid-pipe? I was thinking I could weld on a hanger and attach it to where the DP and mid-pipe bolt together here:
As you can see here, the only hanger is at the other end of the mid-pipe:
As I posted in the other thread, from my experiences, flex pipes exploding/falling apart are generally due to having too much slop in the powertrain mounts. If you're still using factory engine and transmission mounts, that might be your problem... they might need replacing. The transmission mounts (front and rear) will be the likely culprits here, since they are what are meant to keep the engine from torquing itself out of the engine bay.
Do you still have the heat shield on the rear transmission mount? If not, that's going to be part of your problem.
I have ZZP mounts on the front and rear but I do believe there is a slight crack in the front mount. I haven't yet inspected the rear. The mounts have 45k miles on them. I do have the heat shield on the rear mount. The upper mount is the original factory mount.
I've always run the OEM top mount and I don't think it deals with engine torque really, but I could be wrong - been a while since I looked at its bushing. I'd check the F/R trans mounts.
If you have the ability to press things, I'd bet money they're just using a control arm bushing from some other GM car. Powell's first iteration used Volkswagen R32/Audi TT CAB's. I think he eventually switched to using Impala CAB's.
No idea what ZZP uses though, but they SHOULD be fairly easy to source. After looking at the pictures they have online, they do look similar to the R32 bushings, but those generally have some stuff cast into the rubber... they might be cutting/grinding it off to keep their secret safe though. I can measure my '86 GTI's bushings if you want though, to see if they're the same.
So I finally managed to get under the car and inspect things. First off, here's what's left of the downpipe:
Here's the front bushing, I couldn't get a good shot of the rear but it was in marginally better condition. While they show some splitting around the grommets I don't know how much that's actually affecting them. I measured the diameter with a calipers (without removing them) and found the OD is 54.5mm/2.15in.
I can measure my '86 GTI's bushings if you want though, to see if they're the same.
