I've several threads and pics that show the cat placement in two places. I'm going to be running cats with my LG pros and on Lous website it shows that LG headers, cats, then x-pipe. But in the directions and on a lot of the how to installs i have seen posted it shows the LGs headers, x-pipe, then cats. Which is it??

 

It will work either way! I have seen them installed both ways.

 

Well, LG installed mine in Sep, 05 and they put the cats after the headers and before the x-pipe. They also used all 4 sensors. I believe this was a change about a year ago..

 

It will work either way but was recommended to place them after the x-pipe, of course I found this out after my install. I left them ahead of the x-pipe and everything is just dandy! I have an older version of the pro's so I am running sims for my rear 02 sensors (also no problems for at least 2 years).

 

I was on the phone with LGM the other day and asked the same question. The response was cats first then x-pipe. If I remember correctly this topic came up awhile back on the Forum. Traditional thinking is that the cats need to be near the header to get the heat they need. However, the RT cats don't need as much heat so LG recommended putting them after the x-pipe. I guess it really doesn't matter which way you do it!

 

If your using 4 O2 sensors with the LG setup you have to run the cats up front. The cats have to between the O2 sensors, with no crossover anywhere between the cats. I think there is a VERY slight performance (power not emission) advantage to running the cats behind the X-pipe.

 

This is exactly what i was thinking. The cats have to between the O2s to get the in/out readings. And i also thought that have the cats in front would/could only hinder a BIT of performance. My other question then is if i put cats up front do i still need the O2 extensions?? Thx for all the help guys, can't wait to get these installed and hear the new beast. Looks like i'll be setting it up like this:

 

The "best" thing to do is buy another set of rear O2 sensors and put them in the front and use the square 4 pin to flat 4 pin adapters. The rear O2 sensors have higher wattage heaters and since the O2 sensors are so far down stream with headers the lower wattage front O2 sensors sometimes will not work correctly and sling codes at you. I picked up a pair of Bosch rear O2 sensors at the local parts store for around $75 each. Many people have run the factory sensors with no problem, but many has had problems.

Be sure you get your O2 sensors hooked up correctly! The left front sensors must be hooked to the left side flat 4 pin connector, the right front to the right flat 4 pin connector. Don't cross them, it is easy to do the way the come out at an angle. But the rear left O2 sensor must hook to the right 4 pin square cable, and the right O2 sensor connects to the left 4 pin square cable. The rear O2 sensor do cross.

Also, is LG still shipping the fiber header gaskets? If so don't use them! Get a set of the older style factory GM gasket, they work great with headers and normally never leak. You shouldn't use the ones for your 2004 as they are oval ports. Just order a set for a 99 C5 coupe and you will get the round port gaskets.

 

You might want to also read on what the law has to offer. I don't know for sure, but I think I remember when I lived out there that the smog laws specifically say that you can not have a crossover pipe ahead of the catalytic converters.

 

That is true.

I installed the Cats BEFORE the x-pipe. My reason was so I could effectively use the rear O2 sensors. LG installed bungs into my X-pipe for the rear sensors.
When doing this I also needed extension cables for the front sensors to get them to the far end of the headers.

 

A couple years ago I installed the LG Pro's with the RT cats. The guys at LG said to put the cats first. Everything was fine except I could not get the exhaust tips to stay aligned because the connection at the cats wouldn't hold. To cure that I took my car to the local muffler shop and asked them to tack weld the connections to keep them in place. Lo and behold they welded the cats to the x and the x to the intermediate pipes all the way around the connections! That wasn't what I wanted but was okay since they were all straight. However, when I changed from the Stingers to the GHL's I had a bad alignment on the tips and of course I couldn't adjust anymore!

To fix that I've had to order a new set of cats, x and intermediate pipes, an expensive solution, but the tips are off so much I can't stand to look at them. My current setup uses the sims and works fine. In the picture above it looks like the x-pipe has a bung in it for the second set of o2 sensors. Am I going to have to take the sims back out and use all 4 o2 sensors when I get the new pipes?

 

If your currently using simms and are happy with that setup simply plug the rear O2 bungs in the new X-pipe. I picked up some really cheap ($1.25) import oil drain plugs which is 18mm X 1.5 and they worked great, even came with a little copper gasket. Since the drain plugs are not stainless you will want to coat them with a crap load of anit-seize. You may be able to find them at a quick lube place. The hardest problem I had was finding the oil drain plugs without the magnets, I didn't need the magnets since I was putting them in the exhaust!

 

My setup right now works fine and I really don't want to mess around with removing the sims, etc! Your idea sounds great - thanks for the suggestion!!

 

P.S. You said you found an import oil plug that fit into the bung. Would any bolt that fits work fine with anti-sieze on it?

 

Thanks for the great info, i do plan on using all 4 stock 02s and just wanted to be sure about the O2 wiring, so front is left-left, right-right, and the rears go left to right, right to left?? Also I didn't get any O2 extensions in my kit, was i supposed to?? I did note on one of the install pages that they said not to use those gaskets as well and i got the recommended LS1 gaskets, thanks. I'm planning on gettin these installed tuesday but now i'm not sure i can without the O2 extensions.

 

Did you not get any O2 extensions or adapters? You will need extensions or adapters to complete you install. The factory O2 sensors have 4 pin flat plugs for the front, and 4 pin square plugs for the rear. LG used to ship their headers with the 4 flat plug to 4 pin square plug adapter which was about 4" long. Then you threw away your front sensors and moved your rears sensors up front and used the supplied adapter to hook them to the front harness. That forced you to use O2 simulators for the rear or edit them out in the PCM. If your using all the factory sensors you need the flat plug to flat plug extensions of at least 12". But some people has had problems using the factory front sensors since they have lower wattage heaters. If you buy an extra set of rear sensors to run in the front you need the 4 pin flat plug to 4 pin square plug adapter. If LG didn't ship any plugs with the headers they should supply you with a set. You just need to figure which setup you want to run. I would recommend buying 2 more rear O2 sensors and using them up front. So you would be running 4 rear sensors, two up front two in the rear. You know you won't have any problems with codes. Hope that all makes since.

Your correct, up front left>left right>right, and for the rear left>right and right>left.

 

Yeah i want to run 4 O2 sensors, so guess i have to buy 2 more rear O2 sensors?? and get the adapters from LG. This is becoming a project. Didn't know i had to buy other 02s and adapters and other gaskets. what are the chances that with tuning the stock sensors will work ok??

 

Anything that will fit the hole will work as a plug. But I don't think that is a standard thread for bolts. It is the same thread as the really old huge spark plugs if you have any of those laying around. What ever you use it only needs to be about 1/2" long. I used oil drain plugs because they were the right size, thread, length, came with a gasket, easy to find, and the price was great. Below is a photo of my setup, I installed extra bungs for wide band O2 sensors in the top and I also installed two bungs facing down so I had easy pre cat access if I ever needed it on a dyno. You can see the drain plugs in the bottom bungs in the photo below.