This hopefully will help in future questions. There will always be new people to engines. I made this for my other home, at florida3s and thought I would share it here.
First off, you may be wondering...
"What is a precat"
A precat, or pre-catalytic converter, is like a filter for your exhaust fumes, much like your main cat. For those new to motors and 3S's, a catalytic converter is like a honey comb like compound placed inside a metal tube, as part of your exhaust. A catalyst is a chemical which speeds up or reacts with another chemical in chemical changing state. So, in turn, a catalytic converter reacts with your exhaust gas to lower nitrogen oxides, and carbon dioxide, which both are normal compounds from your raw exhaust fumes. With a catalytic converter, your car is safer for the enviroment.
Your next question may be...
"If I have a main cat, why do I have precats"
Good question. The answer is, your catalytic converter contains rare metals such as platinum, to work correctly. Metal expands when it is heated, and thus, it must be a certain size to work correctly when you are driving around town to the local Taco Bell, city driving. When you first start your car, your cat has not had time to heat up, and does not do its job filtering your exhaust, because it has not expanded. So what do they do? They stick in "precats" directly after your exhaust manifold, that way your car is not polluting the enviroment during warm up. That whole 3-5 minutes....
After your main cat finally warms up, you have no need for your precats right?? That's right!! But!!! They are still there, and still restricting your exhaust. They are pretty much permanent.
Now I know you are asking yourself
"Does my 3S have precats?"
Here is the list.
1st Gen 3000GT's/Stealths (1991-1993)... The TT models do. N/A's don't, although they are both called fed-spec.
2nd Gen 3000GT's/Stealths... Sometimes. Some 3S's in 1994 and 1995 were "hybrid" and kept the fed-spec feature. The Cali-spec were thrown into the mix with precats, if your car has an O2 housing as described below. All 1996's had cali-spec.
3rd Gen 3000GT's - Yes... Now fully cali-spec.
"Why did you say they are permanent?"
They are, to a degree. I call them permanent because of the use of O2 sensors. You have 2, or 4, in your Cali-spec. The first, or before your precats, are used to tell your ECU if your car is operating correctly by measuring the O2 in your exhaust, directly after your exhaust manifold. The sensors past your precats are used to make sure your precats are doing their job.. Damn them!
"What can I do about them?"
Gut them! Take off your downpipe, chisel out the icky honey comb stuff, and leave your O2 housing clean as a whistle...
"Won't that throw a check engine light, since you just said the O2 sensor was there to make sure it was doing its job?"
Not if you get an O2 simulator (
www.3sx.com), which sends the correct voltage to your ECU from the O2 sensor, making it think everything is working correctly, even though you just took on a big DIY job.
The 96+ are the only ones that need the 02 sims
"Why gut your precats?"
The answer is simple. If you have a twin turbo, you will notice your turbos spooling up much quicker. Personally, I have a N/A, with just a K&N drop in filter.. woo hoo. My peak RPM for power used to be 4,500 and drop. After gutting my precats, I pull hard up to 6,000. It also sounds bad ass.
"Is it hard to gut them?"
It was fun for me, took me about 9 hours with my buddy, goofing off. I started at 6 p.m. and finished early 3 a.m. using just a chisel.
"What about a test pipe? I hear about them on FL3S all the time."
A test pipe just replaces your main cat, which is 24 inches of the same crap. I am waiting for mine from 3SX, and hopefully I will pull way hard up to my redline with the combination of kitty-less-ness.
"What's the catch?"
It's not exactly legal... But we live in Florida, and no smog checks.. But this is a mod of the... off road racer?
If you live, or move away, and only have your modded 3S, and on your way to Taco Bell realize you aren't street legal and realize you have a smog check coming up, just get it checked after driving your car around for about 30 minutes where your main cat is working at its fullest. Tisk Tisk for you driving an enviroment polluting car.
And most importantly
"Where are the precats?"
The precats are located after your exhaust manifolds. After the gas begins to hit your downpipe, it actually runs into your O2 housing first, which is part of the downpipe. The flange meets up with the 2.5" or 3" manifold, and with the precats inside, looks like a bloated tube. After the exhaust finishes being cleaned, it finishes through the rest of your now straight downpipe, to your main cat. You can tell if you are fed-spec or cali-spec by looking beneath your exhaust manifold and determining whether the downpipe remains one diameter, or "bloats" and increases with diameter.
*You will only be able to check the front, because the rear is hidden by a lot of engine stuff..
"Where can I get more information and pictures?"
Here is the sight for gutting them. Even if you don't gut them, you can see what the O2 housing looks like, as well as the downpipe, and so on.
http://www.3si.org/forum/f1/gutting-...h-pics-318074/