Installing Stock Cats with LT Headers
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02-21-2012, 10:40 PM
Join Date: May 2006
Location: Gilbert, Arizona
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Installing Stock Cats with LT Headers
Since this has been brought up, and I am tired of going back and forth between 3 different threads trying to explain it, HEMI1980, I'll go through the setup that is currently on my truck.
Lets start by taking a look at the stock system from the cats back
As you can see in these two pics (not off my truck) the catalytic converters are welded on, not bolted. They are bolted further up the system to the stock logs. If you were to install shorties that is where they would bolt up to, no moving of anything just plug and play. Those who want to keep the cats with Longtube headers though should note that if you simply cut the cat and keep the existing piping from the cats back you would be pushing that piping pretty far back, close to if not into the transmission pan.
So what are the options.
One way is you can get an adapter to convert the 3in collectors down to the 2.25/2.5" cat pipingand then have a shop fab up a custom Y pipe that isnt nearly as long as the stock setup to make more room, pick up a magnaflow Y and have a better flowing Y pipe. IMO though, that is keeping a lot of the restriction from reducing the pipe size so much.
Another, like I have on mine, is to do a bit of fab work.
I have a set of Pacesetter LT's
I picked up a Pacesetter ORY (Off-Road-Y) Pipe, it's made entirely out of 3in piping, so no reductions.
(ignor the swaybar kit in the box)
Take the piping that connects onto the header collector and mark both sides evenly about 4-5in down and cut the pipe. (Sorry no pics of this step but you will see in a few).
Next cut the cats off the stock piping taking note of direction and side. Take the piece of piping you cut and put it on the end of the cats and trace out a circle. Cut the cat on the trace mark or slightly under, this will give you a 3in opening on both sides of the cats.
Get both cats situated on the header collectors so that the drain plug is pointed down.
Then mock up and tack together the rest of the piping onto the other side. and weld it together. I chose to weld together the enitre Y assembly, however, I left the connection to the header collectors and connection to the straight pipe leading to the muffler attached via clamps. This makes it easy to tear down the engine for additional mods such as heads, swapping headers, swapping mufflers. Also weld in some rear O2 bungs for the rear O2 sensor and, if you have one, the bung for a wideband O2 sensor.
The end result looks like this
Connection to the header (suggest that if you clamp it to the header you cut reliefe cuts in the connection on the Y pipe so it is easier to remove)
Connection after the Cat
Welded rest of Y
Of course you can also choose to go with no cats and make life simple, I however found that with no cats I lost a big chunk of my lowend. Added them back it and the lowend came back.
You can also buy some Magnaflow High flow cats and do a 3in ID on the inlet so the header collector just slides onto the Magnaflow cat and a 3in OD on the outlet so the pacesetter ORY can slide over it and install them that way.
Regardless of choice, there are options for having Longtube Headers on your truck without sacrificing the cats. Hopefullly this clears up some confusion on the subject.
Lets start by taking a look at the stock system from the cats back
As you can see in these two pics (not off my truck) the catalytic converters are welded on, not bolted. They are bolted further up the system to the stock logs. If you were to install shorties that is where they would bolt up to, no moving of anything just plug and play. Those who want to keep the cats with Longtube headers though should note that if you simply cut the cat and keep the existing piping from the cats back you would be pushing that piping pretty far back, close to if not into the transmission pan.
So what are the options.
One way is you can get an adapter to convert the 3in collectors down to the 2.25/2.5" cat pipingand then have a shop fab up a custom Y pipe that isnt nearly as long as the stock setup to make more room, pick up a magnaflow Y and have a better flowing Y pipe. IMO though, that is keeping a lot of the restriction from reducing the pipe size so much.
Another, like I have on mine, is to do a bit of fab work.
I have a set of Pacesetter LT's
I picked up a Pacesetter ORY (Off-Road-Y) Pipe, it's made entirely out of 3in piping, so no reductions.
(ignor the swaybar kit in the box)
Take the piping that connects onto the header collector and mark both sides evenly about 4-5in down and cut the pipe. (Sorry no pics of this step but you will see in a few).
Next cut the cats off the stock piping taking note of direction and side. Take the piece of piping you cut and put it on the end of the cats and trace out a circle. Cut the cat on the trace mark or slightly under, this will give you a 3in opening on both sides of the cats.
Get both cats situated on the header collectors so that the drain plug is pointed down.
Then mock up and tack together the rest of the piping onto the other side. and weld it together. I chose to weld together the enitre Y assembly, however, I left the connection to the header collectors and connection to the straight pipe leading to the muffler attached via clamps. This makes it easy to tear down the engine for additional mods such as heads, swapping headers, swapping mufflers. Also weld in some rear O2 bungs for the rear O2 sensor and, if you have one, the bung for a wideband O2 sensor.
The end result looks like this
Connection to the header (suggest that if you clamp it to the header you cut reliefe cuts in the connection on the Y pipe so it is easier to remove)
Connection after the Cat
Welded rest of Y
Of course you can also choose to go with no cats and make life simple, I however found that with no cats I lost a big chunk of my lowend. Added them back it and the lowend came back.
You can also buy some Magnaflow High flow cats and do a 3in ID on the inlet so the header collector just slides onto the Magnaflow cat and a 3in OD on the outlet so the pacesetter ORY can slide over it and install them that way.
Regardless of choice, there are options for having Longtube Headers on your truck without sacrificing the cats. Hopefullly this clears up some confusion on the subject.