xr4tic

I recently installed a <a href="http://www.randomtechnology.com/">Random Technology</a> high-flow cat. Part number 922510 (as listed on the site) and is for 99-01 A4s.
I got it from <a href="http://www.lightningmotorsports.com">Lightning Motorsports</a> which is a Random distributor, and sells for about 10% less than through Random.
Cost was $315 + $10 shipping. Random didn't have any in stock, so it took about 3 weeks before I got it.

<b>Performance:</b>
So far about 2000 miles of driving (over half that mileage is highway), no check engine lights, and it definately pulls harder to redline then before. This a plus since I have the taller 2.8 gears. After installation, I found myself cruising the highway at 75-80mph in 3rd gear, and running it up to 100 mph (6500 rpm) just for the heck of it I didn't notice a big change in spoolup, it has slightly better off-idle response, but it would probably make a more noticeable difference on a K04.

<b>Comments:</b>
The cat is 50-state legal, and is made of stainless steel. It is perfectly legal to install as long as the stock cat is at least 5 years or 50,000 miles old. It's illegal to remove a properly functioning cat, but it's hard to prove a cat is bad, and a good excuse is to say that you accidentally ran leaded race gas for a while and destroyed your cat (or so I've heard

For the price ($325) I expected a little more. I measured the inlet and outlet inside diameters, and found they were slightly smaller (about 0.1") than stock, but the actual pipe length was shorter on the inlet, and centered on the outlet, maybe that helps with the flow.
Maybe the newer model cat has smaller inlet/outlets?

RT
Inlet: 2.4" id
Oulet: 2.05" id

Stock:
Inlet: 2.5" id
Outlet: 2.125" id

IMO, I think they should have used 3" od inlet and 2.5" od outlet, or at least same size pipe. Most of the people considering this upgrade have aftermarket exhausts anyways.
Plus, it requres a slight mod to fit properly (see below) It also required new bolts (3 bolts, 3 nuts, 6 washers, 3 lock washers)
I think I used 5/16" bolts, about 1.5" long (they required 1/2" wrench, I think 8mm bolts would be the metric equivalent)
New gaskets are recommended as well (you don't want to have to pull it apart AGAIN do you?) and I beleive Random has an install kit that contains new gaskets available separately.
The price is cheaper than the other options though(custom, TAP, and EVO)

I think Juan and CMH were talking about making a cat and dp, it might be worthwhile holding out and see if it gets done, and how well it works.

My car is a 97, and I thought they were all the same. I was wrong.
Apparently, the downpipe and cat were changed sometime after 97 (not sure when, 99.5 maybe?) Luckily, I had a downpipe from a 99.5 on hand (Thanks Doug!)
If you have an older model, you should be able to get your hands on a newer model downpipe from someone who has installed a true cat back exhaust (Borla for example)

Cat comparison:
<img src="http://home.comcast.net/~xr4tic/images/rc_compare.jpg">

<img src="http://home.comcast.net/~xr4tic/images/rc_compare2.jpg">

Downpipe comparison:
<img src="http://home.comcast.net/~xr4tic/images/rc_dps.jpg">

The 99.5+ dp is shorter. If you look at the inlet flange on the RT cat, it has more of an angle, which is why it the dp is shorter.


<b>Removal</b>
First, remove the cat to downpipe bolts (13mm I think)
Remove the O2 sensors (22mm, 7/8" will work in a pinch) Be careful not to twist the wires too much and strain them (I ripped open the wire jacket on one of the wires. Oops)
Remove the cat to turbo nuts (17mm, a "shorty" wrench is a BIG help here)
Pull the cat out.
If you need to remove the dp too, then loosen the exhaust connector below, and also the spring mount.

The cat to downpipe bolts are a PITA, and I could not get them off (even with it out of the car I couldn't remove one of the bolts). If you cant get them off you will have to pull the dp out with the cat. If this is the case, make sure no small children are around, because you may begin swearing. A lot.
There are two ways:
1. From the top:
Remove the dp connections from below, slide the cat off the turbo, and start pulling, twisting, cussing, until you get it out. You also have to be careful of the flex joint, if it bends too much, it can break. Mine did, but I had another dp, so I wasn't worried.
2. From the bottom:
Easier, but takes longer.
Remove the dp connections from below. Remove the driveaxle heat shield, remove the trans mount (make sure a jack is under the trans, jacking the trans up may provide more room)
Slide the whole unit out. Sounds easy, but the bolts for the heat shield and trans mount are a PITA to get to (I think they are allen bolts as well) But you are less like to break something this way.


<b>Installation</b>
Okay, now that everything is out, the rest should be easy, right? Not exactly.

I went to put the cat on, but one of the seems/lip hit the exhaust manifold. Time to grab the hammer. Maybe the newer model manifolds are different?

<img src="http://home.comcast.net/~xr4tic/images/rc_mod2.jpg">

<img src="http://home.comcast.net/~xr4tic/images/rc_mod.jpg">

It's a lot harder to get the nuts back on, because there is less space to get in there.
Once that's done, you need to install the downpipe. My old cat had nuts welded to the back of it, the new one does not. The order goes bolt/washer/flange/flange/washer/lock washer/nut. This requires some patience, it's pretty tight in there, and you will drop the bolts/nuts/washers a few times.
If you removed the cat/downpipe from below, this will be easy since you can do the same thing for installation.
Then just finish up. I found I could not attach the spring mount to the exhaust because of the different downpipe. Must be the mount changed as well.

Installed pic
<img src="http://home.comcast.net/~xr4tic/images/rc_installed.jpg">

Sammay

I was wondering is the high flow cat that you have going to pass smog?

And do you think I can replace the cat with a bypass pipe (tube), so I don't have to spend $3xx for a high flow cat?

xr4tic

It is 50 state legal.

A bypass tube is not. A bypass tube will also give DTCs for the second oxygen sensor being out of range. I think you can get a custom chip to get around that though.

Sammay

What is that stand for?

xr4tic

Diagnostic Trouble Codes, which cause the Check Engine Light to come on

ftodc

If you can have someone do a little fab work you, you can get a high flow 2.5" or 3" universal cat from Summit Racing or Jegs for a little more than a $100. In the end it may not be that much cheaper(after paying for fittment) but you would get a true high flow cat with larger inlet and outlet.