PPE Header and Downpipe Installation
By: Willow 

Pre-Install Preparation:

To reduce chance of seizure of the nuts holding your stock Cat to the exhaust and header; and those holding the heat shields, you could spray WD-40 liberally on them a day or two before the actual install.  I did it only 1 hour before the real work began but was fortunate that no nuts broke. They have been known to break, esp. the 2 nuts holding the main cat to the exhaust.  Potentially the nuts in the worst condition would be those holding your Cat and exhaust together. My car is only 1 year old and it look well rusted.  The upturn edge of the flange only make things worse by making a water holding tray of sort so that retained water has time to work on the rust.  It is out of reach, about 12inch downward away from the top of the left side of the exhaust heat shield. [Editor's note: Products like Liquid Wrench or PB Blaster do a slightly better job of loosening rusted nuts than WD-40]
I inserted the supplied tiny straw into a larger straw to direct the jet spray towards the nuts.
The second sets of 3 nuts (holding Cat to header) to be prep has to be accessed from the bottom.
The 6 nuts holding the heat shield should also be WD-ed. (Shown in next two pics)

Tips: It is best to do the spraying when your engine has cooled (at least an hour) as you'll need to wriggle your arm and spray can thru the narrow gaps. Touching some parts is almost inevitable, to my arm's dismay.


Heat-Shield and O2 Removal:

This process is only being described with a 2-sentence instruction in PPE's installation manual. It frustrated me the most as I had to hunt for the screws holding the 3-piece shield while the engine bay was still very warm and I had to hoist my car up and down a couple of time to locate them all, WD-40 the rusted ones and and remove them. (12mm)
4 screws hold the top heat shield in place, 2 side screws hold the 2nd rear facing piece. Only 2 of the 3 shields need to be removed, the third comes off with the header.
This is the "upskirt shot" of the nut pointed to by the left dotted arrow in the previous pic. Another nut is on the opposite side of the flexible pipe.
We didn't have a proper o2 sensor removal tools, but knew that they are 22mm. I can't reach the hex-ring of O2 sensor with an open-faced spanner with the heat shield still in place, yet can't wriggle the heat shield out with the two O2 sensor still attached due to them pointing at different angles. [Editor's Note:  The proper O2 removal tool is a deep well socket with a slot in the side of it for the wire to come out.  They are available for about $10 US.]
I found that by lifting the heat shield  slightly, I could insert the open-faced spanner to reach the hex and loosen it with just 1/4 turn, then unscrew it by hand.
After the left O2 is out, I could rotate the top heat shield and reach the right O2 sensor.
After disconnecting both o2 sensor connectors and removing the top heat shield, the 2nd heat shield comes off easily.

 
Main-Cat removal:

Main Cat is a straight forward removal as long as the nuts aren't thread seized.
Spray some lubricant (WD-40 again) on the rubber hanger (3) before removing nuts (1) and (2). It will help greatly in the retaining rod sliding out later.

Remove both Cat-to-exhaust nuts labeled (1) first; then remove the three Cat-to-header nuts (2), supporting the weight as you remove the last nut as it would swing down hanging on the rubber hanger (3).

Using pliers or flat head screw driver, slide the retaining rod out of the hanger(3).
A little surprise. It seems that JDM Cat does not come with a 3rd O2 sensor!  You Yankees would have to look for it and remove it before the above steps.

This cutout is where US spec may have your O2, which is not in JDM as shown in this picture. 

 [Editor's Note: Nope, it is where the pink arrow is]
 

Header Removal:
While the car is still hoisted (or jacked up), remove the two nuts holding the brackets that is secured to the header. (Not needed for holding PPE header) 
From the top, remove the 5 nuts holding the header, and slide the header out and down from below.
 

PPE Header install:
After throughly cleaning both sides of the gasket, the engine block where it goes on, we applied this gasket paste for a secure fit.   

[Editor's Note: The gasket is intended to be installed without any sealant of any kind]
With no O2 sensor to insert for JDM model, we manage to buy a fitting nut that screw on flushed. An old O2 sensor w/o wire would have worked but I didn't want it to impede airflow unneccesarily.
The PPE header then goes in (There's just enough space to maneuver it in from the top). The 5 nuts is enough the hold the much lighter header w/o heat shield (9 lbs vs 19.2 lbs) securely. Gasket paste that oozes out and any oil on the pipes are thoroughly wiped to reduce smoking during start up later.
 

PPE Downpipe Install:

Insert the rod on the downpipe into the rubber hanger.

Place the supplied gasket at the end to be connected to the exhaust. (You can just see it where the arrow points). Loosely screw on the 2 original nuts so that you have some freeplay to position the other end into the header. (The PPE instructions indicate bolting onto the header first but I find this way easier for me.)
Couple the downpipe end over the header end and rotate the two brackets to line up.
There are 2 bolts of differing length supplied, the shorter one with a spring within. At first I thought one of the bolt was wrongly shipped, but from the picture below, you'll see that as the 2 pipes are at a slight angle, the distance between the 2 brackets at both ends are different, near at the left side in the pic.

After these are tightened, go back to tighten the bolts connecting the downpipe to exhaust.

 

Precat O2 sensors wiring modification

The O2 sensors wires have to be modified so that the signal from 1 sensor goes to both adapters. An extension wire is supplied for the mod.

After plucking out the two precat O2 sensors, you have to cut both at about 2-3 inches from the adapter. You'll eventually need only 1 sensor and both adapter. Keep the spare sensor in case it is needed in future. After stripping the outer rubber wrap, I cut all 4 wires at where the arrow points.
Though crimping connectors are provided, I decided that a good soldering job is more secure and reliable.

Remember to slip in the supplied heat shrink wrap beforehand.
 

After soldering, individually wrap each solder point with black tape. Then pull the heat shrink over them and shrink it.

Which wires to connect to which are clearly indicated in PPE's manual. It is the same for both adapter and the sensor. You can see that the end of the wire to be connected to the O2 sensor is already marked by PPE with a label at point (2). (Label already removed in the pic).

(1) is connected using "crimps" which is already attached by PPE. I soldered connections at (2) and (3).

Then screw the O2 sensor into the bung (at the collector of the header) and route the wire back to both connectors. Small cable ties are supplied by PPE to hold the wire in place.


O2 Conditioner for Main Cat signal

As my JDM does not have a sensor for the Cat, I did not have to do anything here. I took a look at the Zip Lock bag containing the Conditioner and the instruction is clear and look simple enough.