Thread: exhaust dramas

I tore the front out of the round cat on a rock so just cut them both out and had replaced with straight through pipe. Only $120-, sounds better, flows better and most importantly post change dyno test has more power and same emissions.

New Cats are about $300 each. The sound you can hear is the internals of the cats which have broken up rattling about. If you don't replace them they could either clog or pass the pieces down further and cause a restriction.
If you want to go to headers they are $550 a set and will have to be modified to suit new cats and O2 sensors. You can leave the cats out but then you will be very illegal with the potential for large fines.

It may not be your cats. Check your exhaust manifold flanges. These can come loose and blow out the gasket, creating the noise you're talking about.

The flange connects to the manifold on each side of the engine, just above the cats.

Fixing these is a much cheaper proposition than replacing the cats.

I've recently replaced my whole exhaust as the cats went like yours. Got extractors fitted, with new cats (illegal for exhaust shops to not fit them), a single muffler and bigger pipe. Sounds heaps better but had real problems getting the job done properly. The shop cross threaded a couple of bolts in the head and even left one out and the pipe touched the vehicle in numerous places. Luckily (sort of) had the vehicle booked in to do the heads so they got helicoiled and they also modified the pipes to fit properly. Just make sure the muffler shop wants to do the job before they start as like anything disco, they are not easy to do.

Thanks for all the replies!

I can garentee it's not the flange gaskets that is causing the problem, they are brand new (2000kms old) when I rebuilt the engine, and diagnosed the noise to the cats using a mechanics stethoscope, there is no noise before the cats, but thanks for the suggestion though, it's good to go at it at all angles!

To prevent any further blockages I'm
Not going to be driving the car until I've replaced the failed parts, hopefully to keep costs down I can still save the muffler. And from the price is the headers that geedublya said I'm thinking I might stick with the standard headers, but going to ring a few places tomorrow to get a few comparisons, after the 10 grand that I've spent on repairs since I've owned the car (it should be alot more but I fitted the.rear suspension and rebuilt the motor myself) I don't really want to spend over a grand on the exhaust!

Thanks again for the replies, greatly appreciated!

Stick to the std cast units and have them ceramic coated (keep under bonnet temps down & stops rusting) and just have some better down pipes and the rest made up.

1.3/4" for the down pipes, have them flanged at the top of the Y and coated as well. 2" for the Y (coast as well if you want to help keep the floor cooler), and 2.1/2" for the rest.

I had similar issues with my V8 & found that my rattle was coming from a broken weld on the protection plates that surround the cats. Just got under her, held onto the plates and bashed away on the pipework with my other hand, did this both sides. So, when I went to pipe man & had the 44g drum cut out of the tubes & replaced with straight through pipe, he tacked the protection plates back on & bobs ur aunty. Sounds great but I'm thinking I might get the rear box cut out too now

If you are not sure that the noise comes from broken heatshields or internally, remove the y-pipe and test it. I replaced both cats with aftermarket: 2.25" Magnaflow, ordered from US (ebay) for $250 including shipping. Here is a link how to fit it: http://www.discoweb.org/cats/index.htm