You cant put cats directly behind headers
05-08-2010, 06:41 AM
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You cant put cats directly behind headers I bouught my 2002 Z28 new and one of the first mods I contenplated was an exaust syetem. I bought a new set of kooks long tubes and brought the car to a local muffler shop that did custom stainless exaust. I told the manager that I wanted him to install the headers and weld cats, pipe and mufflers. He told me that "you cant put cats directly behind headers" as they will dislodge the honeycome. I didnt think that sounder right. I would up buying a kooks catted y-pipe and a B&B triflow cat back and installing myself. All was fine until I recently took the car to the track after installing 243 heads and a TR230 cam this winter and I have had a header rattel ever since I came back from the track. Last night I removed the y-pipe and sure enough one of the honeycombs was just floating around the cat. Is this typical? Was the manager correct in is statement or just a random example? Id like to hear your experiances before I order up another $500 y-pipe. For now I just gutted what I have but eventually I may need to go back to cats.
05-08-2010, 07:50 AM
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It is possible for a catalytic converter with a ceramic or cordierite substrate to melt/deform when exposed to that kind of heat. Look into a cat with a metallic core.
05-08-2010, 11:05 AM
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Factory cats are much larger than aftermarket ones which in turn absorbs or can handle more heat. It seems to makes sense. Your new H/C produces more flow and hotter temps so having to them mounted right off the headers probably made them hotter than what they were designed for which is why they failed.
05-08-2010, 04:42 PM
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You're unlikely to make enough heat to melt a zirconia
honeycomb. Headers cool the exhaust gas more than
factory logs anyway. But thermal shock is another story.
Go from idle-cool to full heat in a couple of seconds,
and it's like squirting water on a light bulb.
Spun-metal "high flow" cats, like come with the Jet-Hot
Y-pipe, seem to "disappear" over time despite being
maybe 2-3 feet back from the header collector.
Metallic substrates will fare better with thermal
shock, but don't expect them to last forever.
It's not like 2 more feet is going to save your ***,
how much heat can you really shed at WOT when
the gas spends way less than a second traversing
that extra distance?
You might consider next time, having the shop put
flanges on the cats, and fab you some flanged pipe
to match, so you can save the cats for when they
matter and keep them fresh.
honeycomb. Headers cool the exhaust gas more than
factory logs anyway. But thermal shock is another story.
Go from idle-cool to full heat in a couple of seconds,
and it's like squirting water on a light bulb.
Spun-metal "high flow" cats, like come with the Jet-Hot
Y-pipe, seem to "disappear" over time despite being
maybe 2-3 feet back from the header collector.
Metallic substrates will fare better with thermal
shock, but don't expect them to last forever.
It's not like 2 more feet is going to save your ***,
how much heat can you really shed at WOT when
the gas spends way less than a second traversing
that extra distance?
You might consider next time, having the shop put
flanges on the cats, and fab you some flanged pipe
to match, so you can save the cats for when they
matter and keep them fresh.
