Bad cat = screwed! ;(...but their is a silver lining in this!
Thanks for the help though! I'm installing my headers tommorow so the heat shields are going anyways. You know of any 'easier' way to get to them?Ok, going from memory here but I contacted (almost positive it was Eastern) about there direct fit replacement cats for the GS400 and confirmed that they use a ceramic core instead of the stock and more expensive metal substrate core (OEM). While ceramic functions it will not flow as well as the stock core. Unfortunately I am unaware of any direct fit aftermarket cats with the metal substrate cores.
Secondly, the GS400 only has 2 catalysts. The GS400 does not have a cat in the Y pipe. The GS430 has 3 catalysts with one in the Y pipe.
The stock Y pipe is slightly under 2 inches OD. Using a catalyst with an outlet pipe size of 2.25" will create some flow loss as it will create a "step" between the cat pipe outlet and the Y pipe inlet.
One contributing condition to catalyst failure is fuel mixture. Too lean increases exhaust gas temperature and too rich increases catalytic action both conditions can increase in cat operating temperature. This reduces catalyst life. Tuning our engines to a leaner operating condition to increase power MAY reduce catalyst life. OEM are definitely my first choice but at $1k each they will not be my replacement choice.
Catalyst flow is a combination of catalyst core material, shape, area and cell count. Generally the LOWER the cell count per inch the LARGER each cell is and the HIGHER flow the core is. This is especially true of metal substrate cats that use a metal "foil" which wraps in a spiral fashion that resembles a "screen" as you look at it. Ceramic cores are usually even rows of small square holes with the area between each hole being thicker than the thin foil of the metal core.
Below is a high flow metal core and a high flow ceramic core. Notice the larger holes on the spiral shaped metal core. The pictures are not to scale. Try to imagine the metal core diameter being the same as the ceramic and you should get the idea of the higher flow.
Secondly, the GS400 only has 2 catalysts. The GS400 does not have a cat in the Y pipe. The GS430 has 3 catalysts with one in the Y pipe.
The stock Y pipe is slightly under 2 inches OD. Using a catalyst with an outlet pipe size of 2.25" will create some flow loss as it will create a "step" between the cat pipe outlet and the Y pipe inlet.
One contributing condition to catalyst failure is fuel mixture. Too lean increases exhaust gas temperature and too rich increases catalytic action both conditions can increase in cat operating temperature. This reduces catalyst life. Tuning our engines to a leaner operating condition to increase power MAY reduce catalyst life. OEM are definitely my first choice but at $1k each they will not be my replacement choice.
Catalyst flow is a combination of catalyst core material, shape, area and cell count. Generally the LOWER the cell count per inch the LARGER each cell is and the HIGHER flow the core is. This is especially true of metal substrate cats that use a metal "foil" which wraps in a spiral fashion that resembles a "screen" as you look at it. Ceramic cores are usually even rows of small square holes with the area between each hole being thicker than the thin foil of the metal core.
Below is a high flow metal core and a high flow ceramic core. Notice the larger holes on the spiral shaped metal core. The pictures are not to scale. Try to imagine the metal core diameter being the same as the ceramic and you should get the idea of the higher flow.
Lexus Champion
Joined: Feb 2001
Posts: 3,124
Likes: 32
From: Texas
All I know is the replacements I bought looks exactly like the OEM ones they replaced. The outside shell is even the same. The inlet and outlet pipe sizes are the same. I know and knew at the time when I purchased these aftermarket cats that it has a ceramic substrate and NOT the oem metal type that has precious metals in it. IMHO, with a 10yr old car it would be stupid of me to drop $2400 bucks just for new cats with perhaps slightly better flow. I am all about performance and I would be the first one to say that I have not noticed a difference in performance...perhaps because I went from failing oem cats to new aftermarket cats. All I know is, it works, the car rides fine, I am able to pass NYS inspection and I do not get anymore CEL codes. All while saving a TON of money. IMHO this was the most intelligent choice.
Lexus Champion
Joined: Feb 2001
Posts: 3,124
Likes: 32
From: Texas
Haha. It'll be a hard feat to find a pile of leaves that tall here in SoCal. Thanks for the help though! I'm installing my headers tommorow so the heat shields are going anyways. You know of any 'easier' way to get to them?
JBrady, as always you're posts rock! I really hope it isn't my cat going and it's just a loose heat shield because i'm NOT going to pay $1k each for OEM cats and really don't want to lose any power with aftermarket. Is there a way to test and see if the cat's on it's out of nine lives?
Thanks for the help though! I'm installing my headers tommorow so the heat shields are going anyways. You know of any 'easier' way to get to them?JBrady, as always you're posts rock! I really hope it isn't my cat going and it's just a loose heat shield because i'm NOT going to pay $1k each for OEM cats and really don't want to lose any power with aftermarket. Is there a way to test and see if the cat's on it's out of nine lives?
The O2 sensors AFTER the cats will throw the codes IF any leaks are occuring in the system which would allow MORE oxygen then specified. This is why and exhaust leak will make the ECU "think" a good cat is below par. Make sure to use new gaskets, tighten evenly and securely.
The manifolds have heat shields and the cats have heat shields. The header install removes the manifold shields only. The cat shields stay on. When the cats are off look at the internal cores. They should look like the picture I just posted. Hold them up to the light and you can see light through the cores. If so, they are fine, reinstall. If they are damaged, melted, loose particles, no light... replace.
The O2 sensors AFTER the cats will throw the codes IF any leaks are occuring in the system which would allow MORE oxygen then specified. This is why and exhaust leak will make the ECU "think" a good cat is below par. Make sure to use new gaskets, tighten evenly and securely.
The O2 sensors AFTER the cats will throw the codes IF any leaks are occuring in the system which would allow MORE oxygen then specified. This is why and exhaust leak will make the ECU "think" a good cat is below par. Make sure to use new gaskets, tighten evenly and securely.
Lexus Champion
Joined: Feb 2001
Posts: 3,124
Likes: 32
From: Texas
There is a gasket between the manifold/header and the cat and there is a gasket between the cat and the Y pipe. They are slightly different sizes, larger at the 3 bolt, and are round rubber type gaskets. Call the dealer directly and they can pull up the numbers (I have them elsewhere) and are around $10 each.
I am quoting jbrady, "The stock Y pipe is slightly under 2 inches OD. Using a catalyst with an outlet pipe size of 2.25" will create some flow loss as it will create a "step" between the cat pipe outlet and the Y pipe inlet."
This inner step, from the exhaust manifold to the aftermarket cat, could possibly be minimized with some basic exhaust shop labor. Take a ~footlong section of 2" i.d. standard exhaust pipe. Then using the flange/sleeve maker end of a standard exhaust bender you could stretch both ends ever so slightly until they fit tightly against the inside wall of the south-end of the aftermarket cats, 2-1/4" inner diam. Then just cut both stretched ends off this pipe into whatever length/depth seems appropriate for the inner part of these aftermarket cats then add a few tacks and its not going anywhere.
If you consider that the step is really ~1/8" all around the inner diameter and the steel piping you use as a sleeve is rougly 1/16" then you have smoothed this transition out some. Prob. better than the orig 1/8" wall creating a ocean surf/ backward effect with the air. This is still likely more work then many exhaust shops would want to do but the difference in these cats ~$400 for both vs. ~$2000 for oem, you have a good bit of cash savings to pay for a hour or so more of labor.
This inner step, from the exhaust manifold to the aftermarket cat, could possibly be minimized with some basic exhaust shop labor. Take a ~footlong section of 2" i.d. standard exhaust pipe. Then using the flange/sleeve maker end of a standard exhaust bender you could stretch both ends ever so slightly until they fit tightly against the inside wall of the south-end of the aftermarket cats, 2-1/4" inner diam. Then just cut both stretched ends off this pipe into whatever length/depth seems appropriate for the inner part of these aftermarket cats then add a few tacks and its not going anywhere.
If you consider that the step is really ~1/8" all around the inner diameter and the steel piping you use as a sleeve is rougly 1/16" then you have smoothed this transition out some. Prob. better than the orig 1/8" wall creating a ocean surf/ backward effect with the air. This is still likely more work then many exhaust shops would want to do but the difference in these cats ~$400 for both vs. ~$2000 for oem, you have a good bit of cash savings to pay for a hour or so more of labor.
Last edited by ChampGS3; Jan 26, 2011 at 07:38 PM.
Hey guys, i actually found an exhaust leak in the transition right before the second y pipe. This could be what's making that sound. But there is also a ticking type sound from the front left manifold area. I'm starting the header install tommorow so we'll see if that clears anything up. I'm guna use plenty of the copper gasket silicon i got.
Just as an aside...however somewhat releated to this thread. As far as exhaust leaks go, can anyone recommend a type of sealant to put in, around and between seams/joints where pipes bolt together. I think I have had the same exhaust leak for ever and when I was gettng my headers installed a while back my mechanic said that the flages can't be tightened anymore...and there still is a slight leak on the passenger side IIRC. The exhaust leak sound is VERY noticable for the first 5 minutes upon start-up. After that you barely hear it when the car is warmed up. It kind of makes the car sound like an old-school muscle car (it's the best way I can describe it). The exhaust tone smooths out after the car is warmed up a little. No CEL/codes ever came up...perhaps it's because the leak (if there is even one) is so small.
In any event is there any type of selant you can recommend?...even if permanent that's fine; I don't plan on ever removing these headers.
In any event is there any type of selant you can recommend?...even if permanent that's fine; I don't plan on ever removing these headers.
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sepukku
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