I've heard that if you pull the CAT off and break all the honeycomb inside, it'll make the exhaust deeper/louder. is this true? if so, what side-effects would I encounter if I was to do it? EG-Extra fuel consumption, lesss performance etc.

thanks in advance,
-ian

I've heard that if you pull the CAT off and break all the honeycomb inside, it'll make the exhaust deeper/louder. is this true? if so, what side-effects would I encounter if I was to do it? EG-Extra fuel consumption, less performance etc.

thanks in advance,
-ian
1) Will sound tinnier
2) doesnt do anything for performance on a stock 2nd gen (4cyl V6, whatever)
3) your muffler is very different to mine, so could posibly make it sound louder, cant hurt.

']1) Will sound tinnier
2) doesnt do anything for performance on a stock 2nd gen (4cyl V6, whatever)
3) your muffler is very different to mine, so could posibly make it sound louder, cant hurt.

I'm not looking for an increase in performance, just dont want to lose the little power that IS there.lol.i'm just looking to make it louder without spending a great deal on it. Will it increase my already horrible fuel consumption?

I'm not looking for an increase in performance, just dont want to lose the little power that IS there.lol.i'm just looking to make it louder without spending a great deal on it. Will it increase my already horrible fuel consumption?

If you want to make it louder, take out any middle muffler or resonator you have and replace it with pipe. Cost me $40 to do it.
So i have from cat back just pipe to 2 mufflers and as type40, Boozer and Nemesis can tell you its pretty loud

Replace it with a straight pipe.

']If you want to make it louder, take out any middle muffler or resonator you have and replace it with pipe. Cost me $40 to do it.
So i have from cat back just pipe to 2 mufflers and as type40, Boozer and Nemesis can tell you its pretty loud

i was standing behind it when you started it...yes it's relatively loud. thanks for the info bout the resonators, dint think about 'em. lol

$10,000 fine from the epa if they catch you

$10,000 fine from the epa if they catch you

coolness = priceless

']coolness = priceless
lol

don't hollow out your cat, otherwise the RSPCA will have you arrested for animal cruelty. Also you are a sick weirdo if you do :bowrofl:

it's definitely illegal to hollow any kind of cat.

don't take this the wrong way, but dont be an idiot. don't touch the cat unless changing to a higher flowing unit or it is stuffed. if you want it louder, remove secondry mufflers if there is any there or change the main muffler.

running without cats is for leaded fuel, older diesel and race cars.

A cheap upgrade is to find a larger cat of a car with a larger motor from the wreckers. Example find a cat in good condition from a V8 Commodore or Falcon and fit ti to your car, it'll pretty much be high flow on your engine.

In a previous car I owned (not current car), I needed a new muffler - so got a sports muffler fitted.
When i picked it up, the guy said she's a bit louder than expected, because my Cat was hollow - just the shell - totally clean inside.
As neither myself or the previous owner (person I trust) had touched the Cat - we guessed it had disintegrated by itself and had been spitting out bits with the bigger bits being what had destroyed my muffler. Something like that :confused:

End result was that I had an exhaust system with an illegal hollowed out Cat BUT I had not been the one to hollow the cat out - it had done it itself.
I wonder what would have happened if I had been pulled over for an EPA check in that case.

In this case, the exhaust was not tinny - it was deep and loud. But this may depend on the car and what other mufflers, etc. are on the exhaust.

My advice would be to buy a sports/hi-flow Cat if you want to.
Hollowing out a cat could be a defect/fine you could do without.




$10,000 fine from the epa if they catch youIs it really that much??!!! :shock:

Is it really that much??!!! :shock:

from what i have been told, yes that is the case.. but you know people can be like...

Don't hollow it out.

If you want to gain noise/power buy a hiflow one and get it fitted.

Unlike the EGR cat converters are worth-while.

if u have ugly stock cat thats half dead can make a world of difference, turbo cars benefit, but yeah in the end, big fat fine for a big fat hollow meow.

through the grape vine is $5000 per cylinder.... same as running race fuels on the road totally illegal.

TBH you will probably loose alot of your bottom end due to the lack of backpressure...
And ists also been said that you can loose power with a Hi Flow cat if not running forced induction. Go to a larger standard type cat if anything. A common occurance is backfiring on backoff with hollowed out cats.

through the grape vine is $5000 per cylinder.... same as running race fuels on the road totally illegal.

TBH you will probably loose alot of your bottom end due to the lack of backpressure...
And ists also been said that you can loose power with a Hi Flow cat if not running forced induction. Go to a larger standard type cat if anything. A common occurance is backfiring on backoff with hollowed out cats.


i hollowed out mine a while ago before i had the 2.5 and it had more of a bleh bleh bleh sound and when i backed of the accelerator it backfired through the exhaust. i fitted a new stock cat and got the 2.5 fitted and it sounds better and still backfires through the exhaust (i love that sound). its just not worth it though A. a big fine and B. defectable.

Dont be stupid, risk vs reward makes this one a no brainer

and it's bad for the environment

Dont be stupid, risk vs reward makes this one a no brainer

and it's bad for the environment

not being stupid. i was asking so that I DIDNT make a stupid mistake...

thought thats what these forums were all about. :doubt:

thanks everyone for the info.

i heard a while ago, of people basically sticking broom handles up thier exhausts to bash the crap outa the cat because they thought that it was hurting performance - but when they punched holes thru thier cats the engine, ended up hurting performance and increasing fuel usage...

basically... dont make holes in the cat!

i heard a while ago, of people basically sticking broom handles up thier exhausts to bash the crap outa the cat because they thought that it was hurting performance - but when they punched holes thru thier cats the engine, ended up hurting performance and increasing fuel usage...

basically... dont make holes in the cat!

1, its damn near impossible to do this through the tailpipe because of mufflers/bends.
2, in 99% of cases it wont make economy or performance worse.

But yeah you got the last point correct! "dont make holes in the cat!" :D

I purchased mine off a stock KR verada and it was completely empty....:s So i guess im in the same boat as puck

']I purchased mine off a stock KR verada and it was completely empty....:s So i guess im in the same boat as puck
I'm dobbing you into the EPA...:P

1, its damn near impossible to do this through the tailpipe because of mufflers/bends.
2, in 99% of cases it wont make economy or performance worse.

But yeah you got the last point correct! "dont make holes in the cat!" :D

i was able to do it on my other car, the broom thing...i coud get a 1"x1" of pine up to my front pipe, i had the whole straight pipe thing happening years ago on the 180. 1 bend at the diff, and was 3.5"ID staino pipe no muff or res or cat

hollowing out my cat on my other car, cost me performance, since it all didnt come out and a large chunk was wedged in sideways.

for a 2nd gen v6, the manifold and front pipes are going to cause to much restriction for a hollow cat to make any diffference. On a non-turbo there is no such thing as too little backpressure, the less backpressure you can obtain, the more ignition timing you can wind in, to a point ofcourse, this in turn resolves the problem with loosing bottom end torque with a larger dia. exhaust.

just buy a high flow cat it will get a bit louder.

Btw a hollowed out cat still has 2 restrictions. The enlargment and shrinking in pipe diameter.

My hi flow is a 2.5" so the honeycomb sits at 2.5" from memory. Would flow better than a hollow im betting.

Ps my car is really quite loud. The dohc is half the cause.

cats are there for a reason, if you want to do something with it get a high flowing one, not that expensive, dont just hollow it out.

I had a big burn mark on my Charade from following a GTi-R around the track which dropped its cat on to the Charade. It happens when you lean mixtures out and really get up a car.

I had a big burn mark on my Charade from following a GTi-R around the track which dropped its cat on to the Charade. It happens when you lean mixtures out and really get up a car.

and this has what to do with anything? :gtfo:
i hate cats.

instead of hollowing it out just run a section of piping up through the cat. this has the effect of making it straight through and it looks stock from the outside no copper would see the difference.

You can smell the difference though - its pretty obvious.

Cat's (not the sort that meow and like milk) run within a set temperature range, if you hollow them out or put a pipe through, they won't then be at the set temperature.

All the epa (or whatever they are now called) do, is test the temperature of your cat at normal engine operating temperature, if it is not within the range, they know something is up.

Then it is $10000, thanks for coming. Like everybody says, it aint worth it.

The EPA, AKA the fun police :badgrin: can also order a 3 or 5 gas analysis to be performed on the car too IIRC.

It would be a pretty easy matter to measure the temp of the cat with one of those non-contact laser thermometers...