Dynabob

Thinking about taking off the front y-pipe on my 89 this weekend and cutting out the pre-cats and welding in some pipe. Anyone ever done this at home? Any tips? Welding is no problem for me.

65Z01

One of the restrictions of the stock front Y is indeed the two pre-cats; the other is the waffle bends in the 2 1/4" pipe which considerably narrows the pipe.

AGENT 86

I was going to do it myself, had a look and decided to leave it to the pros. Plasma cutter made quick work of removing them. They then bent the pipe and flared the ends, slipped on and mig welded them. I was out of there in 30 min

Greg88

Here in California, our cars are subject to a visual inspection as well as a "sniff" test at the tail pipe. Cutting the pre-cats was not an option. My pre-cats had partially dissolved in my '88 Coupe when it had about 160,000 miles. The debris went straight to the inlet of the main cat. There the debris blocked about 80% of the screened opening. My Vette lost a lot of power, especially above 3,500 RPM.

I had to find a way to un-clog the exhaust and keep Mr. Smog Test happy. I dropped the "Y" pipe and completely punched out the pre-cats. I was able to run a chain through each pre-cat and drag it back and forth. This broke loose all the remaining material in the pre-cats. Now, even though the pre-cats are hollow, they will pass the visual external inspection.

Of course, I still had to install a new 3-way main cat (from Random Technologies) to ensure my Vette would pass the tail pipe sniff test. It passed easily. In fact, it got lower emissions readings than it got when the pre-cats were functional.

Added bonus: I recovered all lost horsepower and maybe even gained a few extra by dropping backpressure below factory level. Also, the sound of the exhaust is a little louder and deeper.

I did this procedure about 3 years ago and I am still very happy with the results.

Good luck!
Greg S.

GIJoe

Both of my pre-cats blew their load within a week of each other. I just pulled the main cat off, pulled out the stuff that came from the pre-cats...then while I was at it, rammed out the main cat...so baiscally i have a free flowing system right now..it sounds much better too (a bit raspier) and seems to have gained a bit of upper end hp too

Plasticman

I did this recently. It turned out real well, but takes some time. It is not visible, so the Smog ****'s would never know.

1. Undo the shields at one of the crimped edges. Lift the exposed edge, and peel it away slightly, so that the 2 shield halves can be separated, and then slipped off the shields from the cats (only one edge on each cat needs to be separated). There are small tack welds that are easily broken (in my case). If the tack welds on your cats are stronger (better), then you may have to drill them out, or use a Dremel tool.

2. I then drilled three 1/2 inch holes in the top of each cat. One hole towards each end of the cat (about an inch inward from each end), and one in the middle.

3. Using a large screwdriver and solid metal rods (and a BF hammer), I was able to break apart the cat matrix material. The 3 holes allowed complete access to the length of the cat to the screwdrivers/punches.

4. Note that there are "sealing" rings at each end of the cat matrix (a total of 4 rings for the 2 pre-cats). These rings need to be removed also so they don't come loose later, and get into the main cat. Could cause a rattle or minor blockage. The rings can be difficult to get out, but once the screwdriver edge catches it, it can be deformed and comes out the pipe.

5. After the Pre-cats are gutted, I put a steel slug (from a metal electrical box) over each hole, and welded the holes up. I then painted the welded up area with some high temp aluminum paint. Then reinstalled the shields, and recrimped the edges (I also retack welded the edges), and painted the shields and pipes.

Hope this helps,
Plasticman

jackdaroofer

Probably just a cheap to buy the pipes without the precats...stainless should be under $200

BigTodd

Pre cat's gone, and muffler eliminators, the only thing left is the main cat, my 88 sounds like a Vette should sound.

Runum

I bought some 2 1/2" mandrel bent J tubing from Summit and fabbed my own precatless front Y pipe. Using a plasma cutter and mig welder it cost about $100. I can email pics of it if you want. I do run a Random Tech 3" main cat and I have passed emmisions every year(2) so far. Good luck with yours.

gear-head2

I would suggest that "hollowing out" the precats may actually hurt performance as the exhaust velocity slows as it enters the now larger precat chamber and then has to speed up again. I think the right way is to replacing them with a straight pipe.

jsinga

I did mine like GIJoe after a pre-cat grenaded and plugged the main cat. Used an old piece of 1/2 in iron pipe about 6ft long and BFH. Bent the pipe until it fit down the Y pipe and hammered away.
Cost "$0"

js

yellow dragon

my local exhaust shop could not legally pull out the pre-cats for me, but thats here in washington so i hope its different elsewhere