I've done some searching on here and haven't been able to find my answer. I'm pretty much looking to a diagram and an explaination of how the GS400 exhaust system looks like and works. At what part are the 02 sensors at? I know the car has quite a few mufflers/resonators and cats. For you guys that are running catless are you using 02 defoluers to not throw a CEL. That's why i'm really looking for the location of where the 02's are. Thanks

 

There's two on each side ( 4 total). One before the cat and one after.

 

So how far down(where) the exhaust are the 2nd set? Basicly I'm trying to see what I can replace with just pipe before reaching an 02 where I would throw a Cel.I'm trying to visualize what the entire system looks like but obviously having some issues here.

 

About 6" after the flange coming off the cat. It is well before the two into one collector. After the front flanges it necks down quite a bit. I haven't measured though. You could cut it off at the flange and run larger tube. You can buy O2 bungs on Ebay for around $10 a pair shipped.

 

I heard there is 2 cats in the factory system. Are they off after each side of the header(being close to the header)? I'm trying to replace as much of the oem exhaust without throwing a check engine light. I don;t know if you can get your hands of a diagram of how the oem exhaust looks like for me? I've been searching all over the web and can't come up with much.

 

Yes, they are off the manifold, well after the first O2. I'll have be back under it tomorrow. I'll take a pic.

 

Yeah if you could take pics section by section of the entire exhaust set up that would help me a ton and point out the locations of the 02's. Thanks a ton I really do appreciate it

Rob

 

Take a look at this. This is from a 430 but guess it might be similar.

 

Ok, thanks....

So the 2nd picture down there is that large pic that looks like a big H or maybe Y you could say. At the very bottom(where it starts as one) is that big thing a cat or a resonator or a muffler? Can you replace that entire thing with out it and have just pipe with out throwing a check engine light?

 

It's another cat but I don't know if you can replace it with a pipe and not have problems such as emissions when you have an inspection?

 

We only have an "check engine light" emissions in NH. If removing that 3rd cat and you WON'T throw a check engine light, then you'll pass. So I guess that's my final question. By looking at the placement of the 02 sensors, if I remove that 3rd cat will the car trigger a check engine light. Anyone that knows for sure one way or another please post up, thanks.

 

On the GS400's there isn't a cat after the Y, just a resonator/muffler. I also took a pic of the O2 on the drivers side. The tube diameter at the flange is 60mm. It quickly necks down to 50mm before the second O2. The Y connection is 70mm and also quickly necks down to 60mm going into the resonator. The tube diameter coming out of the second Y, going into the long resonators is also 50mm but they squeezed it to clear the unnecessary horizontal brace.

 

nice pics.....

 

Thanks for the pics....

I went to a local custom exhaust shop today. I have an appointment for tomorrow morning at 8am. They are going to replace the Y pipe that connects to the 2 cats and the Y pipe that connect to the oem mufflers with 2.5 inch pipe, no resonators and 2 flowmaster 40 series mufflers. Should that do the trick or am I losign anything? You mention that some of the stock pipe is 70mm (2.75) and triggers down to 50mm (2.00) I'm going to be running 63mm (2.50) all the way back.

 

I think the stock exhaust narrows down based on the theory that the exhaust cools as it makes it way from the engine and becomes harder to push out. By making it narrower it keeps it warmer and easier to push out. Wider is not always better. Or it could be the reason many cars have donuts for spares. $$$$.