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Posted by Eclipse98Spyder, Oct 18, 2006
Bolt-on Tech - 4G63 intake, exhaust, intake manifold, ignition, fuel system, cooling, etc.
Just look at getting a new OEM cat, OR pick up an aftermarket one with a carb certification.
If there's a way to clean it, then it beyond me. Usually you just replace a clogged cat and call it a day for another 100k or so.
1) Steel rod through the center
2) Test pipe
3) Replace the cat with new.
The catalytic converter contains a ceramic catalyst, not pieces of metal.
ceramic honeycomb coated in precious metals like platinum which eventually it all melts and blocks the holes in the honeycomb. so your both right.
But you all got it more or less.
As an N/A gutting the cat may be ok. I wouldn't recommend it for a turbo car though. But if it were me, i'd just replace it and call it good for a while.
rich- unburnt fuel firing off inside the cat melting it down.
Just out of curiosity, why do you not recommend it on a turbo car?
"The best exhaust is no exhaust", under that principal you want as clean of a flow as possible. Hence why we opt for mandrel bending over press or crush bent.
Think about it, you're going to flow a gas through a pipe, that pipe will then open up into a larger chamber, then close back down. Where that pipe closes back down the exhaust gasses will be trying to squeeze back down. Causing them to run into eachother, and into the walls of said chamber creating turblance. This turblance will hinder flow as the exhaust gasses continue to bombard around trying to go from big to small. Again, the same reason a press bend is bad.
But in an NA car, you don't have to worry as much about this, because though it will increase flow to a point, it still will be creating back pressure.
But if you're that worried and want a test pipe, just hack the cat shielding off, and tack it around the test pipe, so it looks like a cat.
If your cat is bad replace it, that is the nest solution.
Gutting cats years ago when they still were filled with pellets offered a power increase because the pellet style cats were so incredibly restrictive. This just isnt the case with modern honey comb style cats.
Granted, the open chamber creates turbulance in the exhaust but the catalyst in the converter actually creates more restriction. Even with the catalyst still intact, the flow patten is almost identical to that of a gutted cat. The catalyst just adds restriction to the turbulence that is created by the larger chamber. Airflow through a gutted cat will surpass that of an intact cat. Turbo or non turbo, this still applies.
May pass inspection but will the sound db be louder? I would almost assume so
Honey comb style cats have linear flow paths through the catalyst which keep the exhaust flow straight through the cat. Very similar to the honeycombs in our MAS's. Remove them and the air no longer flows as linear and causes turbulance.
so the cat is oval in the middle and tapers down at both ends right? the honeycomb is only in the center full size section. The exhaust goes in a 2 inch hole. has a big cone expanding to 7 inches or whatever oval, goes through the honeycomb then comes out and has the same turbulence again as it all trys to go out a 2 inch hole.
the honeycomb directs it STRAIGHT through it doesnt angle it towards the inlet/outlet or do anything to increase flow.
when i gutted mine i wouldnt say it got louder but the tone changed. got a bit more agressive sounding and you can hear when the stock internal gate opens now.