1STVETTE90

After removing the cat what is the process of hollowing it out, i do ytou just take a pipe and start pounding?
Thanks,
Rick :cheers:

Past_VNE

I have heard that you take a section of reinforcing bar (like for concrete) and pound it through :smash: and eventually all the guts will come out. However, I live in Indiana and we have no emissions, so we have easier ways of getting around that, like welding on a straight pipe and recycling the cat. I have also heard that you can weld covers onto a straight pipe to "fool the mirror guy" if you live in a state like that...Delaware is a good example. Once you do get it opened you will notice that it is louder and performs better too. Just a note, make sure the cat casing is very clean before you put it back together, catalytic converter dust can instantly ruin an engine if it gets pulled back up during a high rpm deceleration. Good Luck!!!

Matt383

I have cat replacement pipe I bought for my '88 along time ago. Never used it. Still shrink wrapped. It was sold as a "test" pipe, or an "off Raod" pipe. Has the fittings to bolt right in.
I'm pretty sure it fits 86-89 vettes. Not sure about '90. Basically you'd have to ask if your car has the same cat as an '88. I was going to post it in the parts for sale section. If it works for you and you want it let me know. I'll post it next week I guess. Any way. Good luck! :cheers:

scorp508

86-91 have the same exhaust fittings so it should work.

ScottsLS3

Its depends if it tries to run or not. If you have your buddy hold it still its not to hard!! :reddevil

dscottr

Hollowing your cats can cause backfiring! I bought my car about 8 months ago, and every time I would get on it and let off gas - pop and bang. Big time annoying. Not just gurgles, I got some real loud bangs, every once in a while. Come to find out the cats were gutted and acting like expansion chambers for gas fumes. This is how it was explained to me. I am no mechanic myself, but I am deleting the cats entirely this week.

The Dingo

Wear a breathing mask when you start hammering the guts out. You can breath in some really nasty stuff if you don't.

USAsOnlyWay

If you are removing the cats completely, but still want to fool the mirror test, I have heard of people welding straight put inside of the muffler and then onto the exhaust system. Thus, no popping and the looks of a cat.
Just an idea....

P.S. If you want more info on the popping sounds there was a whole post about it just a week ago or so.... :flag

Nathan Plemons

Couple of things to point out here. First and foremost, if you do "gut" a cat do it correctly and put a straight pipe through it. If you do this it will function just like a straight pipe. If you do not you are introducing a potentially large amount of turbulence to your exhaust flow and you can ACTUALLY HURT YOUR PERFORMANCE.

Imagine having your exhaust enter into a large chamber where it is going to want to expand then try to force it back out a smaller hole. Either remove the cat and put a straight pipe in it's place or put a pipe through the middle of the cat if you need to pass a visual inspection. Otherwise don't bother.

The "backfiring' is also just a side effect of having a freer flowing exhaust. Ask any person with headers or no cat and they will tell you the same. Essentially the cat is serving as another muffler and you hear it more without it. The situation is made worse if you are running slightly rich and if you have exhaust leaks.

Here's how it happens, first you are running a little bit rich so at WOT you are loading up the pipes with unburnt fuel. When you let off the gas the computer does something with the timing advance and it's possible that for just an instant it fires in a way as to ignite the unburned fuel in the exhaust, causing the loud noise you hear. A few small exhaust leaks help this process along because there is more air in the exhaust along with the unburned fuel. If the exhaust is free flowing enough then you will actually throw a flame out of the tailpipe!

How do I know this? First and foremost I've done it. My car with long tube headers, an x-pipe and flowmaster mufflers has been on the dyno. I had a multitude of small exhaust leaks and the car was running pig rich. The exhaust in the shop made your eyes burn. In any case on my last pull when I let off the gas I fired a 3 foot flame out of both tips. Unfortunately I didn't get to see it because I was driving, but just ask LCVette, he had the same thing happen and has the picture to prove it.

Secondly I've seen it happen at the track before. One of my friends has a Supercharged Mustang that he was racing one night. I was talking to him and asked him what he thought it would run. He said "not as good as it can, I've got it tuned very rich to be on the safe side. It'll probably throw a flame out of the tailpipe when I shift" I didn't really think anything about it at the time until I saw him run. As it turns out I was standing directly behind his car when he took off down the track, when he hit the 1-2 shift he threw a nice flame out of the exhaust.

I later asked him about it and he explained exactly why it happened, something about how when you let off for a shift or suddenly decrease the load on the engine it does something with the timing. I should have paid more attention, I'll have to ask him again some day.

In any event it happens with any car given the right conditions. The cat just quiets this down, sometimes so much that you don't even hear it. A hollow cat just amplifies the sound as opposed to a straight pipe that just carries the sound.

blk90rdstr

This is what i did, and it is the way to go better sound runs great. Yes its gonna gurgle when you let off it but its not really backfiring. Kinda cool actually. I did the hollow cat on my 84 with some dynomax mufflers it ran better but way too loud. If you just want to hollow it you dont got to remove the cat. Just drop the cat-back exhaust and hammer rebar thru it to break the honeycomb media into little chunx. Start the car and rev it up to blow out the chunx. Repeat till empty if necessary. But if possible get the cat sleeved :smash:

GlockLT4

See my website ....

CentralCoaster

Usually if you grab it by the tail, and swing it into a cinderblock wall a few times, its bones will break into small fragments. You might need to lay it on the driveway and use a brick or hammer for the skull. You can then remove most of the fragments with long-nose vice grips without really cutting a big hole in the carcass.

Not sure how this will help your performance though..:U

USAsOnlyWay

Ok, so I was going to sleeve my cat....then I started reading all these posts about the loss in low-end torque, especially for L98's... :skep:

I know this is a little bit OT but I figure if we are talking about hollowing em out might as well talk about the downsides....so my question:

If I have straight pipe back to mufflers, will that be enough back pressure to maintain the low end torque but still free up the flow some?
(86 L98 stock)

And just straight up, is that true or not!?! :confused: Why or why not?
TIA:flag

TA

I can't comment on the effect of gutting the cats on a LT1, but I can tell you there is a definit power gain on the L98 (at least there was on my car). I do not have dyno proof of this, but at the track I gained a solid .10-.15 after gutting the main cat. :yesnod: I guess its possible that my cat was bad and that was what accounted for the gain, but I don't believe this to be the case as I saw no signs of a clogged cat. Later along, I replaced the front y-pipe with a unit w/out pre-cats and again I saw another solid gain at the track. Well worth it, in my opinion, if your area allows it.

_freakmonkeydogboy_

:lolg: :rofl: :lol: :thumbs: no that's funny stuff....