Modifying CAT convertors

[Zoro]

Hi all,
has anyone removed the original cat convertors and drilled out the "guts" to improve performance. Obviously its illegal (if you get caught) but is this an option rather than buying the high flow ones?

[sand_man]

yeah my boss did it on his 5L (he's an idiot).
It made no difference.

[GOTMYN]

Yeh I did it and I lasted a week before I went and had 2 new ones fitted along with a complete new system.
Removing the contents of the cat made no change to the performance, maybe worse, and gave it a tinny sound!! One of the few things I will that I wasted my time with!

Hope this helps.....

[V85000i]

depends though, if you don't have the cash just yet to get a new one, bashing the old one out will improve performance on a 100,000km+ car, because they get worn out and block up, it happend to me, on my old car, it couldn't rev over 3000rpm, discovered it was the CAT, bashed it out and went better than it ever did, but on your car being new, it might not do much.

[GOTMYN]

If your going to do it, don't just empty the cat and bolt it back on... doing this will create a lot of turbulence in the system and you will loose high rpm power!! At least fit a piece of pipe through the guts of the cat, to stop the air entering the cat and spiraling inside it before it exits to the rest of your system..

[Cobez]

Or just buy a high flow one.

They aren't expensive and it saves trouble from the law if you get busted.

[Not_An_Abba_Fan]

Not to mention all the crap you are spewing into the environment without a cat.

[sand_man]

dumb idea full stop

[vr_owner]

a highflow one fitted cost my brother $350. for a 3inch... not sure what brand.

[AttaBoy]

Don't do it. Do it the right way - buy a high flow unit.

If you can't afford it then save up.

[jules]

Not to mention all the crap you are spewing into the environment without a cat.

on anything more than 10 years old, i can't imagine the cat doing anything. the precious metals would be inert or worn away by then.

not that this would be any kind of defence from the EPA

[greenfoam]

I've gteched a 1/4 mile with my car (back when it was slower) with a blown out cat that came with it = 14.7 changed it to a good cat = 14.7. It makes no difference on a near stock car and that was a 5 litre

Edit, I will say though if anyone tells you a bashed out cat makes your car go faster, they are just imagining things because it will make your car quite alot louder and infact it's pretty easy to tell which cars have hollow cats just on the sound, I guess people think louder is faster

[greenfoam]

on anything more than 10 years old, i can't imagine the cat doing anything. the precious metals would be inert or worn away by then.

not that this would be any kind of defence from the EPA

The cats on VN's are solid not just coated like some newer ones, they will last forever or untill they hit something on the road and break into pieces. The metal in them alone is worth 50 bucks at a scrap yard. The reaction that cleans the exhaust doesn't take the metal away

[jules]

a catalytic converter works by means of a chemical reaction. the catalyst is the precious metals inside it, such as paladium and stuff i believe.

by definition the more exhaust flow through, the less catalyst there will be. however i have no idea how long it takes to wear out in practice..

[STEALTHY™]

Don't Risk it.

Pay $200, or pay $10,000 plus maybe jail time.



Its soooo obvious when a car has a hollowed out cat, if i can smell it and i'm not even looking for it, then mr police man is defiantly going to notice.

[Not_An_Abba_Fan]

By design a cat will wear out, it needs to be replaced at intervals. By law a cat had to last a minimum of 40 000kms, now I think it is something like 80 000. The precious metals do indeed wear out, cats need to be tested to see if they are still working. 10 years old or not, if the cat is not working, it needs to be replaced.

[AttaBoy]

By design a cat will wear out, it needs to be replaced at intervals. By law a cat had to last a minimum of 40 000kms, now I think it is something like 80 000. The precious metals do indeed wear out, cats need to be tested to see if they are still working. 10 years old or not, if the cat is not working, it needs to be replaced.

And yet they don't get replaced because mostly they are overlooked by owners and most mechanics. A cat usually stay in there for the lifetime of the car.

[Boonz]

a cat converter will work doesnt matter how old it is.... its just how effectively it works for its age that matters... most people wont pay the money to change a cat over at regular intervals. simple as that. they dont want to pay $200 minimum for something that in their eyes is still doing its job and isnt stuffed... i see this happen all the time with all kinds of parts that are actually worn out.... its frustrating to watch really

[greenfoam]

a catalytic converter works by means of a chemical reaction. the catalyst is the precious metals inside it, such as paladium and stuff i believe.

by definition the more exhaust flow through, the less catalyst there will be. however i have no idea how long it takes to wear out in practice..

The chemical reaction doesn't use up the metals in the cat, unless you bash the cat on a bump or the cat gets damaged but running rich or getting too hot it will last forever x 10 it's the truth I swear

[naf33n]

how can you afford a vy ss and be to tight arse to get new cats put on???

[adam69]

Gutted mine a while ago and it sounded crap and made no difference in power.Glad to get rid of it.

[Bilbs]

i agree with the general oppinion of this thread, dont bash it out, they sound ****, go no better, and when you cosider that im only paying 800 for a TWIN 1 1/4 with 2 metal high flow cats, 2 mufflers, and 2 resonators, add it all up, and the cats wont be much more than about 170 or so each

[Not_An_Abba_Fan]

The chemical reaction doesn't use up the metals in the cat, unless you bash the cat on a bump or the cat gets damaged but running rich or getting too hot it will last forever x 10 it's the truth I swear

An exhaust never stays hot enough to burn all the contaminants in a cat, the cat itself doesn't actually wear out, although this is how it is often described. Exhaust contaminants build up over time and reduces the effectiveness of a cat. Doing a temperature test is probably the easiest way to tell if a cat is still working as it should be. As the exhaust passes through the cat, it heats the precious metal coating, this burns most of the harmful stuff, if this precious metal coating is covered in crap, it won't heat up to burn what it should. Also the ceramic brick that is coated by the precious metals will break down and stop flow, also stuffing the cat.

[Bax]

Interesting, I never really cared how a cat worked. But that's good to read.

I just got myself a 3" hiflow in mild steel for 160 bucks. Stainless was 280.

[Not_An_Abba_Fan]

For future reference, I do stainless hi flow cats for $190.