cat removal for extra power?

[lunchie]

A mate of mine up north just brought a new car (V8 sti), I know what a bastard right? am very jealous.

Anyway he is getting its ecu remapped for more power but was also suggesting removing the catalytic converters in the exhaust and replacing them with steel sections of pipe. Reason for this over a full exhaust is that he doesn\'t want to make it more noisy if possible.

Do you guys reckon this would liberate more power or not?

[ADIKT]

Would most likely free the system up a bit. But to get full benefits he\'d be better to go 2.5 or 3" straight through with a couple resonators in there

[lunchie]

yeah I told him as much but he is flatly refusing to go any louder, stock sti\'s are not exactly quiet as is so I can understand where he is coming from I guess. I imagine it would help boost spool a little quicker too would it not?

[lunchie]

at first I would have told him just to do the whole exhaust but after living with my flatmates stock v6 RA for the last year I was surprised by how loud a stock sti exhaust really is

[johnny5]

Change the downpipe keep the rest and the noise will be fuck all above normal

[Marky]

Yes absolutely it will free things up, it will make it louder also, and I\'m not 100% on the legalities of removing it on a car that new

[Guest]

Dont think you can legally remove them that late. Nuke the light and bash them out. Also you can have a 3" exhaust quiter than stock. Being T/S EL theyll be damn quiet off boost anyway. Loud is a honda with no turbo to shut it up.

[johnny5]

is there a law on removing them bro? removing it wont make it much louder at all at least it didnt with my bug eye then I realised without going bigger I was missing out on unreleased power thats when I went to full 3inch if hes really worried about noise resonators and a quiet muffler will do him. but he can get all the benefits of the above ny just doing the downpipe to a 3 inch jobbie such as

http://www.trademe.co.nz/motors/car-parts-accessories/performance/suspension-braces/auction-593922363.htm

Then keeping the rest stock pretty sure the cat is on the down pipe closer to the heat the better and faster it starts working

[Pappu1]

Agree with Johnny5

Replace downpipe keep rest of system stock

Wil not make alot of sound difference but work wonders for spool and bit more top end

[optmspotts]

 johnny5 said:

http://www.trademe.co.nz/motors/car-parts-accessories/performance/suspension-braces/auction-593922363.htm

This works out cheaper. (Link)

The top (more expensive one) has a high flow cat. The second, cheaper one is just straight pipe - same as the $700 one being sold by Redline. Can work out just under $500 incl shipping iirc.

EDIT: Also, where are people getting this stuff about might be illegal to remove cats on later models?

[johnny5]

 optmspotts']

[quote name='johnny5 said:

url=http://www.trademe.co.nz/motors/car-parts-accessories/performance/suspension-braces/auction-593922363.htm]http://www.trademe.co.nz/motors/car-parts-accessories/performance/suspension-braces/auction-593922363.htm[/url]

This works out cheaper. (Link)

The top (more expensive one) has a high flow cat. The second, cheaper one is just straight pipe - same as the $700 one being sold by Redline. Can work out just under $500 incl shipping iirc.

EDIT: Also, where are people getting this stuff about might be illegal to remove cats on later models?

was wondering that also bout the cats maybe if you live in Australia

[Flat4]

Removing the cat will make it louder if he\'s worried about noise

[newsuba]

Was discussing this just last week.

Basically, if the car left the factory with a cat it has to have a cat to run on the road.

And a word of warning - most modern cars won\'t run properly if you remove the cat.

One Euro dealer told me of a customer who removed the cats on his expensive SUV only to find the ECU having a spazz and putting the car into permanent limp mode.

The fix was two replacement cats at ~$1600 each.

Ouch.

[Kiwi_Fozze]

removing the cat on my v7 sti had little effect on sound. it was more agressive rumble as opposed to a strangled rumble. bit more crackle. no noticable increase in volume, just a different tone.

if ECU throws a fault, find a friendly member with a tactrix cable to give the tune a bit of a tickle to get the best performance from the downpipe change, and turn off the "CHECK ENGINE" light that a cat removal MIGHT throw up.

mine didn\'t throw a fault, happy

[optmspotts]

Another downpipe: http://shopping.kinugawaturbo.com/kinugawadownpipesubaruimprezawrxstispecctwinscrollvf36vf37vf42jdm.aspx

[johnny5]

 newsuba said:

Was discussing this just last week.

Basically, if the car left the factory with a cat it has to have a cat to run on the road.

And a word of warning - most modern cars won\'t run properly if you remove the cat.

One Euro dealer told me of a customer who removed the cats on his expensive SUV only to find the ECU having a spazz and putting the car into permanent limp mode.

The fix was two replacement cats at ~$1600 each.

Ouch.

yup I have seen those downfalls in some cars namely a Ve commodore that started to have problems after the cats were removed. the O2 sensors started playing up from what my workmate said will ask how he got around it cant remember

[Kiwi_Fozze]

Space the oxy sensor out of the exhaust a bit. Anti fouling spacer iirc, big thread on nasooc about it

[johnny5]

 kwi_fozze said:

Space the oxy sensor out of the exhaust a bit. Anti fouling spacer iirc, big thread on nasooc about it

wonder if that worked on his comoodore? Will check up with him.

[Marky]

Some cars have 02 sensors before and after the cats for the purpose of watching they are actually functioning. The vast majority of jap imports do not have this, it\'s more very late model stuff and more commonly euros

Short answer is it will absolutely increase power, as it\'s the equivalent of sticking a steelo pad into your exhaust. However the question on some cars is how much is gained - some cars already have such efficient cats that no power is there to be had. Ditto for the exhaust as a whole - there are some parts which restrict, and some which just lower noise without affecting power - like that big resonator in Subaru exhausts

The thing about late model cat removal - its never been relevant to me but I thought there was noises that after a certain year, you couldn\'t get cert without a cat (but like I said, not something I\'ve had dealings with so don\'t know for sure) in place - or maybe it\'s just a law supposed to be coming in? Pass.

If youre going to the trouble of cutting it out and replacing with pipe, you may as well just do the entire exhaust while you\'re there. If you just want it gone but stealthy... A big steel pipe/crowbar and 20 mins and you have "decatted" the car - or the US guys like to call it a test pipe too. Results can vary between cars as to how effective it is tho

[Disruptz]

I have a custom turbo back, I was queried by the lvv certifier where my cat was, and that in order for the cert I needed to have a cat in there, I told him it was pre turbo, he gave me the benefit of the doubt and off I went with my lvv.

The warning light can be turned off using a logger. Piece of cake.

[boon]

On my V7 we removed the catted downpipe, ECU didn\'t give a single fuck and neither did the certifier.

[Guest]

Im sure its a wof issue after a certain year.

[johnny5]

 boon said:

On my V7 we removed the catted downpipe, ECU didn\'t give a single bother and neither did the certifier.

+1

[Pappu1]

the v7-10 dont give a single fcuk on cat removal

the rear o2 sensor can be removed all together and then the code removed as per post above

[tebbyj]

 SP00N said:

the v7-10 dont give a single darnit on cat removal

the rear o2 sensor can be removed all together and then the code removed as per post above

Really?

There seems to be heaps of stuff on the american and english suby site about changing the down pipe and getting all sorts of issues from just a CEL to rich running..

Does it have something to do with the USDM or EDM cars vs our (mainly) JDM cars?