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Discussion Starter #1 (Edited by Moderator)
Okay - I spent about 4 hours today reading threads that I found using the super snappy 30+ second search engine on this site (PHP - bleh) and I've compiled what I think will be a good 'What you need to know before you start' type checklist for a header install.

Common problems seem to be:
1. Stuck O2 sensors - which are pricey to replac (saw one quote for $290/sensor)
2. Problems removing the header (go through the top or the bottom?)
3. Poor fitment (not so much as of today but back in 2003 this looked like an issue)
4. Exhaust leaks
5. The dreaded Check Engine Light (again - not so much anymore)
6. A tinny / vibrating noise (sounds like a vibrating heat shield) coming from under the car at various points throughout the RPM range if the stock Y pipe is mated to the aftermarket header.

Tools you will likely need before you start:
1. A soldering gun for the O2 sim installation (to prevent CEL) and of course a wiring diagram (more on this later)
2. A 'breaker bar' to get hard to remove / stuck nuts off
3. PB Blaster (lubricant to remove stuck nuts)
4. Anti-seize (to make future removal easier - why don't OEM's use this by default!?)
5. You definitely want to go invest $8-$10 in a O2 sensor socket for a standard socket wrench. This is a socket that looks not un-like a spark plug socket - but it has a line cut down the side where you can stick the wire for the sensor. Trust me - these things are on VERY tight and you don't want to strip these trying to use a spanner wrench etc. I bought a 7/8ths today and it was a bit loose - I have seen other people say they think it's a 20 or 21mm socket. The guy at Meineke only had 7/8th's ones and that's all Meineke uses I guess - they may not make other sizes. :(
7. Your headers may have an extra hole in them for a wideband O2 sensor or some other reason - if you have more than 3 holes on your headers - you need to go to Meineke and get a plug for the exta hole(s). They gave me some for free and apparently this is somewhat common. There are also two kinds - one is a 'flush mount' dealio that screws into the header flush and uses an alan key setup - the other kind is more of a traditional bolt you can use with a socket wrench - haven't decided which one I'll use - probably the bolt so that I can get more torque - don't want it to vibrate loose.

Tips and Tricks I picked up reading the threads:
1. Remove the OEM headers from the top unless you have a lift making bottom access easy.
To facilitate removing the header through the top I strongly recommend removing the lower catalytic converters heat shield before attempting as it gets stuck down low on the control arms or engine bay if you do not. Also remove the engine cover so that you don't break it. People removing from the bottom have found it easier to remove some sort of brace before doing so but I took mine out from the top and all I had to do was remove the lower cat's heat-shield which required removing a bolt and un-crimping some cheap aluminum with a pry bar (its crimped all the way around the cat).

2. I'm assuming given the horror stories I've read about stuck O2 sensors that you want to remove these FIRST while the pipes are still bolted to the engine / car. Tips for removing stuck sensors include:
1. Put PB blaster on all the O2 sensors and the header nuts 30 minutes before removing to try and loosen them up. Don't get any gunk on the tip of the sensor itself.
2. If the O2 sensors are stuck - don't get mideval on their ass - try heating up the headers / pipe by either running the engine for a few minutes to get them hot or by using a blow torch (yeah -because we all have those sitting around right?). Also - if you manage to get the sensors loose but then during removal they get stuck again half-way out - do NOT force them - you will completely strip the threads on the sensor and ruin your OEM headers. If they get stuck - screw them back in and get the engine / headers HOT and try removing them again. I didn't do this and had to buy two new O2 sensors ($74 a piece for the universal Bosch's). The sensors hardest to remove were the top ones near the engine.

3. Using the proper gaskets is absolutely critical if you want to do the job right! Most aftermarket headers these days seem to come bundled with an aftermarket y-pipe as well. The Y-pipe connects the header to the B pipe (going from 2 pipes down to 1) and usually does not have a catalytic converter built-in to it (like the stock Y does) instead it has a resonator where the stock cat would normally be. In my experience with the Alphawerks header + Alpha Y, after several months of driving, I found the 'drone' and loudness of this setup to be too annoying for my daily driver, especially when considering there is probably no noticeable performance gain to be had with this setup. Given this some people install only the new header opting to leave the stock Y pipe on (which I recommend the car stays quieter and since you have a catalytic in the exhaust flow its less smelly). If you install both the header and an aftermarket Y - you will want to use the flat gaskets that came with the header + y-pipe at the header -> Y connection point. If you decide to install only the header and to keep the stock Y pipe - you will want to use the stock Lexus gaskets at the connection between the header -> y-pipe. Do NOT use the gasket that came with the header for this connection - it was likely designed to be used with the flat connection between the aftermarket y-pipe that came with the aftermarket header. The stock Lexus y-pipe is not flat - it has a recess around each of the two pipes where two round 'O-ring' gaskets are supposed to fit. If you do not use the proper, stock Lexus gaskets you will probably have an exhaust leak that may result in a raspy, 'tuning fork vibrating against an aluminum can' type of sound at various spots throughout your RPM range as you accelerate. You will probably also lose some low-end power / pedal response. If you lost your stock gaskets you can get them from your local Lexus dealer for $7/gasket. Here's a link to a thread with some pictures that shows what happens if you use an aftermarket gasket at the header <-> stock y-pipe connection.
You can see the black smoke that has burned in on the gasket in between the two pipes in the middle, where it was leaking out the top which results in the noise and loss of power. Don't do it - stick with the Lexus gaskets if you use the Lexus y-pipe - it's that simple.

4. If you decide to use the stock Y pipe and the aftermarket header - due to the increased flow of gas coming into the stock Y pipe - you will more than likely hear a tinny / raspy / vibrating noise coming from under the car (although it may sound like its coming from the engine bay when in the car). Even with no exhaust leaks you may still hear this. If you do it is more than likely coming from the catalytic converter. I had an Alpha header and a stock Y and I put the car on a lift and had a shop employee rev the engine while I walked around under the car listening. The noise is definitely coming from the stock catalytic converter. I had Meineke cut the resonator out of the Alpha Y pipe and insert a catalytic converter. The resonance from inside the catalytic is still there but its definitely quieter when driving and doesn't resonate / vibrate / rattle as much. A higher quality catalytic (perhaps one encased in thicker metal) may eliminate this problem.

My stab at installation instructions - now that I've done it.

1. Unplug the battery - let it drain while you work - this resets the ECU (someone mentioned hitting the brakes a few times while unplugged to 'discharge' the system).
You'll need it un-plugged for the O2 sim wiring later on anyways.

2. Remove the engine cover and air intake tube and start working on getting the O2 sensors un-screwed (again - PB Blaster 30 minutes before this and try starting with a cool engine - if it doesn't work try again with the engine hot). You will most likely need a breaker bar and an O2 sensor socket. Do NOT screw up the sensors on removal - it's a huge pain in the ass getting new universal ones wired in. If you do end up ruining some sensors - you can get Bosch universals for $74 at any autoparts store. You simply cut the sensor from its wiring harness and wire in the new sensor. There are 4 wires. One wire is the signal wire, one wire is ground and two wires are heater wires. The instructions that came with the universal O2 sensors didn't have information on how to map the wires from the Toyota O2 sensor to the Bosch (it had other makes). I found this site to be invaluable:
The 2001 IS300 is the 2nd one down from the top under Toyota 4-wire. The ground wire is white, the signal wire is blue and the other two wires are the heater wires. That's all you need to know to map those over to your universal sensor.

3. Remove the lower cat's heat shield for easier removal of the headers. I tried getting the headers out without doing this for a few minutes but it was very obvious this needed to be done (either that or removing the throttle body - and removing the heat shield was very easy from underneath the car with it on jack stands).

4. Unscrew the old headers and try getting them out through the top (If you are on jack stands and don't have a lift) with a friend helping you. You shouldn't need to move the engine or remove any extra parts if you do step 3 above.

5. After removing the OEM header - see if the gaskets on the engine manifold are in good condition and able to be re-used. My 2001 IS300 had metal gaskets that were very thin and were in good shape (i.e. not stuck / bent / warped etc.) so I re-used them vs. using the slightly thicker aftermarket gasket that came with the header. Your headers should have also come with a gasket you can use if you like.

6. When screwing on the header nuts make sure you use anti-seize before putting them back on for your eventual turbo / supercharger installation that won't keep your aftermarket headers. :)

7. Install the O2 sensors - make sure you anti-seize them. Also if you have an extra hole in your headers - plug it. On some early Alphawerks headers you may have an extra hole by the firewall due to a design flaw. You can plug it with a plug you can get for free (usually) at your local Meineke muffler shop.

8. Wire up your O2 sim (most header / y-pipe combos come with the O2 sim included) - you need to do this regardless of whether you replace the y-pipe or not since you have removed 2 catalytics (if you only replaced headers) or 3 catalytics (if you replaced headers AND y-pipe). If you do NOT wire up an O2 sim during the header install you will definitely get a check engine light as the result of a catalytic inefficiency code within roughly 500 miles of driving. You can go to Autozone to have them verify the code with an OBDII reader and then wire up your O2 sim and reset your ECU to make it go away.

9. Think about what you want to do with the Y pipe. The Y pipes with resonators are very free flowing. You lose some 'punch' off the line but they are very good on the highway. The downside is that they stink (no cats anywhere) and they are loud (resonator) at cruising speeds. The stock Y pipe provides for more low end torque so its better off the line and provides more head snapping punch. It is also a lot quieter at cruise and stinks far less due to the fact it has a catalytic. However it will more than likely have a mechanical resonance coming from the catalytic converter (I'm assuming due to the fact that its got more air coming at it due to the free flow design of the header) that you will more than likely hear when driving under normal conditions. Its all a trade-off. One option you can pursue is taking the y-pipe with the resonator to a muffler shop like Meineke and having them hack out the resonator and weld in a catalytic. I did this for $170. The aftermarket Y pipes are definitely better than the stock Lexus Y and will mate up to the header better.

Regarding O2 sim wiring: SophieSleeps posted a great pin-out for the various model years for wiring O2 sims - I took pictures of her 2001 model diagram next to the actual wiring harness and then took some close-ups of the actual wires to make things easier for DIY'ers:

NOTE: These are 2001 model diagrams / pics ONLY!
The Sophiesleeps pin-out diagram next to the actual wiring harness in the engine bay can be found here:

Here are close-ups of the actual wires from the diagram - this is the left-most wiring harness on the sophie-sleeps diagram that needs to be modified (the white wire for bank2 sensor2):

Here are close ups of the other two wiring harnesses (the 2nd and 3rd from the left on the sophiesleeps diagram) that you need to modify:

NOTE: I haven't actually wired O2 sims in the above pictures yet!

That's it!
Other things to note post installation is that the headers may / will 'smoke' for a few minutes as the car runs. They are burning off 'stuff' that got on them (human sweat, grease from your hands, etc.). This is completely normal - the smoking will stop after a few minutes. They will also likely turn a nice burnt orange / purpleish / bronze sort of tint after a while - this too is normal.

Okay - now for the links to the threads that I found most helpful after hours of searching:

1. Solder
2. PB Blaster + anti-seize
3. Unplug battery. :)

O2 sim hookup diagram for 2002 models and later only!

Another great diagram for wiring an O2 sim - don't know what model / year this refers to though.[url[/url]

Great pic of an IS300 header install:

Removing from top or bottom?
Great advice - grinding, cutting, braces, moving the engine - oh my!

Great pics of an Alphawerks header install before and after with dyno numbers:

The raspy / tinny / vibrating sound you may hear with a stock Y pipe and aftermarket headers can be found here:

Link to Das Galloway's analysis of whether or not removing the stock y-pipe makes any noticeable performance difference.
It doesn't look like it makes much difference but it is noticeable mostly off the line. When I installed my header initially I swapped out the Y-pipe as well for a cat-free setup. It was loud, there was a very annoying 'droning' sound at 55-60mph cruising speeds, and it was smelly at lights. After a few months, given Das's analysis that there should not be a very noticeable difference, I swapped the Y-pipe back for the stocker. I noticed an improvement in off the line acceleration / initial punch. Also when I swapped the stock Y-pipe back, I didn't put the stock Lexus gaskets back and as a result I had a massive exhaust leak at the header <-> Y-pipe connection initially that made things 'noisy' (to say the least). You could feel the air puffing against your hand if you held it near that connection. It was that bad. Not surprisingly the car sounded like crap and power was down (which led me to believe the stock Y made a huge difference). After I fixed the exhaust leak by purchasing new gaskets from Lexus, the car was noticeably quieter at WOT and my power / responsiveness I had lost was back - it's just like it was when I had the aftermarket Y-pipe - so I have to agree with Das's analysis. If you're going to track the car or not use it as a daily driver - swapping the Y might make sense (if for no other reason than the sound) - but if its your daily driver and car you haul your wife / kids around in - I'd stay with the stock Y pipe - but you may have to live with a raspy / tinny noise emitting from the catalytic converter in the stock Y.

7,564 Posts
i would remove the header from the Top. i have not yet removed it from the bottom, and looks like i have to take the lower chassis apart to pull it through there. Its like trying to get a "Y" through an "O", since the headers are 6 pipes into 2. Remove the intake of course, engine cover, and unclip the o2 sensor harness in the back for the bank 2 sensor 1. it might be a good idea to unbolt the two or was it 3? 10mm nuts(2) and one 10mm bolt that holds the wiring harness and bottom throttle body mount in place.

YOU MUST undo all the o2 sensors first before taking the header out. or else you might break the o2 sensor. spray liquid wrench religiously on it, let it soak, then get a 21mm open end wrench, or the special 21mm O2 sensor attachment, and tap it with a hammer to break it lose. the header and o2 sensor has to be cold or VERY VERY cool. or else you will weld the threading together and strips the hell out of it.
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6,606 Posts
Here's the REAL DEAL to removing the header.

Don't bother taking off the heatshield. And definitely take the header out from the top unless you like doing more work. I've done this now on 3 different occasions and it has worked effortlessly everytime.


This will give you enough clearance to manuever the header out. For just a bit more clearance, have a friend pull the motor towards the driver side although that is not really necessary if you pull it out at the right angle.
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1,042 Posts
Discussion Starter #4
Update: I wired up my O2 sim that came with the Alpha header a couple weeks back and I've since put 500mi on the car with no CEL. By way of comparison after installing the header + y I got a CEL within 250 miles (I believe I got the PS 0420 Catalytic Inefficiency code) so I think I can declare victory. :)

All I used was the 2001 sophiesleeps wiring diagram. I cut the two signal wires and taped them off, and then connected the 2 signal wires from the O2 sim to the harness end. ThenI spliced in to the power and ground wires using a t-tap connector I bought at Advanced Auto parts for like $1. Took about 30 minutes start to finish and everything seems good.

4 Posts

Hello, did you pass smog or not? Let me know how you did
because i got the o2 sim hooked up for about 200 miles and no check engine cell light. Will I pass? email me back at [email protected]

Update: I wired up my O2 sim that came with the Alpha header a couple weeks back and I've since put 500 miles on the car with no CEL. By way of comparison after installing the header + y I got a CEL within 250 miles (I believe I got the PS 0420 Catalytic Inefficiency code) so I think I can declare victory. :)

All I used was the 2001 SophieSleeps wiring diagram. I cut the two signal wires and taped them off, and then connected the 2 signal wires from the O2 sim to the harness end. ThenI spliced in to the power and ground wires using a t-tap connector I bought at Advanced Auto parts for like $1. Took about 30 minutes start to finish and everything seems good.

1,042 Posts
Discussion Starter #6
Holy old thread revival, Batman! Umm... I don't have to pass smog because I live in 'the south'. :) NC used to do a pipe test but now they just do an OBDII scan - so, yes, I would pass that. SC where I live presently doesn't even do e-checks anymore - not even OBDII. :)

424 Posts
What specs do you torque the bolts to? How many lbs/ft?
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