At some point will there be a consise post as to what we need in total to do the headers right (Y pipe, unbolting engine for install?, EGR?, Heat shields fitament, ETC) and a complete price for a kit with everything we need?

I am interested but the length of this thread gets me dizzy...



1. Does the engine need to be unbolted?
2. Can the stock heat sheilds remain?
3. Is there an option to have them delieved heat coated?
4. Will the Y pipe be sold with the headers?
5. What and why would I remove the EGR?

Did I miss anything?

I agree 100%. If you are going through the trouble of replacing the manifolds w/ headers you might as well go the small extra step and have a new front exhaust pipe (i.e. y-pipe) fabricated. Then bolt up a cat back system and beat the s#*^ out of 540's all day long.

It's going to cost me lunch but I'm trying to get my parts guy to make a call to his distributor to compare y-pipe's so we don't have to battle the friggin heat here in Texas by making the comparo ourselves!

Until there is an actual guinea pig questions 1 & 2 will remain unanswered. The repair manual does not have a procedure for removing the exhaust manifolds. However, when removing the heads the exhaust manifolds remain attached until the heads are removed. Hopefully head removal won't be required and a more reasonable method can be used.

1. Unknown, expect to at least remove motor mounts. Actually removing the engine is not anticipated. This is for GS400s. Earlier LS400s and SC400s have already replaced headers without removing engine. I also think the 430s will be easier due to their stock manifold design.

2. No heat shields.
3. Most if not all of the headers will be Jet Hot coated.
4. Not at this time.
5. None of the 1998 and newer cars have EGR, non issue.

That would be great. Let me know what you find out.

Head removal will NOT be required. Access is the only limitation. Removal of the stock heat shields is the biggest hurdle. Once they are out of the way the rest is not bad. This is for 1998-2000 400 engines. The 430s have a narrower manifold which leaves more access room.

On 1998-2000 GS400s you will need headers only. Y pipe recommended. I may be able to offer a Y pipe but I am making no promises. The stock one will work but will be somewhat restrictive. I recommend 2.25" piping on the duals and 2.50 or 3.00 for the center pipe. No complete "kit" is planned.

Waiting for the GS430 still whats the story with this ???

Not sure if this has been mentioned in all the discussion on Y pipes, but I assume you would want to replace the "center" cat (at the end of the Y pipe) with an aftermarket hi flow cat? Random Technology makes some nice products for example, I've used them in the past. Would need to have a flange welded on for the mid section pipe to bolt to...
I know the cats at the end of the manifolds flow well, but this could be a choke point?

Actually, on the GS400s it is a 60mm/2.37" resonator. Yes, upgrading to a slightly larger center pipe and duals is a good idea. Just keep it below 2.25" on the duals.

Hi John, I have two questions:

1. So you recommend 2.25" piping for the pipes that make up the Y pipe, 2.50" or 3.00" for the center pipe (or in my case a 2.50" X-pipe), and then finally 2.25" on the duals leaving the center pipe (in my case the X-pipe) to the resonators?

2. What exactly is the function of the resonators? Is it just to reduce the "loudness of volume" of the exhaust sound? If it is, are we talking a lot of noise, if I removed the resonators and replaced them with 2.25" pipes straight to the mufflers (and of course on the opposite end they are joined to the 2.50" X-pipe)?

I was at my mechanics place yesterday getting the oil and filter changed and I verified that there is enough space for the X-pipe I bought that I want to replace the center cat with.

John, are you sure it is just a resonator? The reason I ask is that I was told by two different Lexus techs that it is actually a cat. Not that they are infallible but still.... If it is just a resonator, I'm wondering how necessary it would be to keep? In other words, it seems like it would be easier to leave off as long as the exhaust sound is not too loud. I'm pretty happy with the Carson Tuned sound level now...
With all your work on these exhausts lately, I would imagine that you are correct on this issue, but it would be nice to know for sure.

It is a catalytic convertor.

This is definitely news to me. The Lexus diagrams that I have do not list the GS400 or my car for that matter. I have never seen a picture or in person of a 3rd cat on a 1998-2000 model year Lexus V8.

Please post a picture. this must be a California required part and possibly Canada?

I doubt this catalyst is too restrictive. If it were mine I would probaby just cut the cat of the factory pipe and weld it to an upgrade pipe. This is only one weld and would be relatively easy to reverse if needed.

Also, Hameed, I would not recommend a 2.5" X-pipe. The idea is to keep velocity high. The bigger diameter will slow the gases. It will work just not as well. Please post a pic or email it to me.

Sorry to ask but.... what is the new date to ready for the headers for the 400's that we know we have a test pair for at this time. ?