De-Cat

[teddytinton]

Has anyone tried decating?In other circles(ford, citroen, renault etc) There seem to be large power gains for removing the cat but i havent seen anything on here on the subject.
I need to get my exhaust looked at because its blowing, i was thinking about removing the cat on my current system, trying it to see for excess noice/power gains and then take it from there. If its too noisy or doesnt make any noticeable to performance then simply get a new system. Any thoughts folks?
by the way i have a 318is if it makes any difference!

[dannyboy759]

Just bought a new centre section for my 325.
It has incresed the torque and it revs more freely which is what i expected it do do.
As for noise it shouldnt be any louder unless you want to remove the cat completely and not replace it with another box but if you going for the same exhaust as i did but with a centre box rather than a cat it wont be any louder just a change in tone.

[1an]

removing the catalytic converter with a straight piece of pipe then you will get more noise.

someone i used to work for had a supercharged lotus elise which was pushing 255bhp! due to the manifold, removal of the catalytic converter, and the rest of the system allowed it to get one of the smoothiest power v torque curves ive seen. According to Dave Walker @Emerald said it was one of the best supercharged kseries engine he has seen and mapped.

personally i would remove the CAT but be preparred to run into MOT issues with emissions.

[agreen]

i would remove the CAT but be preparred to run into MOT issues with emissions.

unless you bung the tester

one of the best supercharged kseries engine he has seen and mapped.

then the head gasket went

[teddytinton]

Emissions is a worry, but i was thinking as its registered before 1992, a cat is not required. But I suppose it will be putting more shite into the atmosphere. Well i was simply thinking of a straight piece of pipe, but "replacing with another box" I dont understand!

[1an]

i would remove the CAT but be preparred to run into MOT issues with emissions.

unless you bung the tester

one of the best supercharged kseries engine he has seen and mapped.

then the head gasket went

shame is was all upgraded hey, this was a car that got thrashed within and inch of its life aswell,

[teddytinton]

i would remove the CAT but be preparred to run into MOT issues with emissions.

unless you bung the tester

one of the best supercharged kseries engine he has seen and mapped.

then the head gasket went

Love the k series comment

[teddytinton]

Emissions is a worry, but i was thinking as its registered before 1992, a cat is not required. But I suppose it will be putting more shite into the atmosphere. Well i was simply thinking of a straight piece of pipe, but "replacing with another box" I dont understand!

[agreen]

shame is was all upgraded hey, this was a car that got thrashed within and inch of its life aswell,

make no diffrence lmao the k series was pre programmed to explode all over the floor

i think rover did a deal with the aa a sort of commision bassed thing

sorry for OT

[Brianmoooore]

If the car was registered, or the engine built, before August '92, then, if the engine is in good condition, it should have no problem passing the appropriate MOT emissions test.
BMW's figures don't show any drop in power for an iS fitted with a cat, but they do show a significant increase in fuel consumption.

[agreen]

but they do show a significant increase in fuel consumption.
_________________

really wow no thats interesting

i wonder why

[teddytinton]

How much fuel consumption are we talking? for alot of other cars there an off the shelf decat pipe, but catn find anthying for mine

[dannyboy759]

An E30 M3
that i de catted had the same emissions read out after it was re moved as when the cat was fitted, and if its a pre 92 car why not get rid of it.

[teddytinton]

Thats what my thinking was! It seems like a massive restriction and potentially could be a cheap way for a bit more power/driveability

[Brianmoooore]

You can decat it by smashing up the ceramic matrix with a steel rod up the end, and pouring the insides out of the pipe. Common practice for LPG cars, as even post '92 ones easily meet emissions requirements without a cat.
The official fuel consumption figures are;
Non cat: 47.9 MPG at 56MPH. Cat: 44.1 MPH
Non cat: 37.2 MPG at 75MPH. Cat: 34.4 MPH
Non cat: 26.9 MPG urban cycle. Cat: 25.9 MPH

[Gibson]

but they do show a significant increase in fuel consumption.
_________________

really wow no thats interesting

i wonder why

something to do with having to run exactly stoicheometric when actually lean would be fine for certain purposes i think... dont quote me on that though. Brian?

dont know what stoicheometric mean? look it up

[agreen]

i had a e36 and took it too kwick fit on a satuday and asked them to cut the cat out and weld in a some pipe to de cat it i asked one of the fitters when he was on his own to do it for cash "leave it with me he said "

took some time becuse the cat was huge but was done and done all in if i gave him the cat and £20

bargin if you ask me but was soooo fing loud and i mean to loud backfired like a mother trucker to for some reason

noticed no diffrence in power though

good luck

[Bob_S]

i doubt you have a cat on your 318is tbh mate but a new section from BMW is worth a look.

I have replaced the centre section on my m3 with a supersprint section and it sounds better, goes better and flames on up changes fuel economy drops but only because cant resist the temptation to give it some.

My 327i has a full stainless steel exhaust on it with a 6 branch, this sounds awesome (being an ETA) and is a really nice piece of kit

[munky30]

You can decat it by smashing up the ceramic matrix with a steel rod up the end, and pouring the insides out of the pipe. Common practice for LPG cars, as even post '92 ones easily meet emissions requirements without a cat.

You'll be using cable ties to mount radiators next brian...

Anyway... a good decat pipe will take 5 minutes to swap with the cat for an mot. Its worth it, just for the noise.

My old mazda had a 'restrictive cat' that was about a foot long and incredibly closely 'weaved'... getting rid of it gave me a couple of horses... and restored the v6 roar to its former glory.

[k10]

I'm interested in this process also.
I like Brian's idea of removing the cat the old fashion way, (smashing with a pipe).
Brian, I have a 2 piece system, does the front section have to be removed from the car to remove the bits of smashed cat, Just seems a hassle removing the front exhaust section on a 2 piece. Is it possible to lift the front to get most of the cat out? I have a new rear section ready to go on and was going to cut the cat out, but leaving the pipe there and smashing the cat out seems a simpler and quicker approach!
I would have thought there must be a few BHP to be had on a 325 by removing the cat. My only evidence for this is that my 2 pre 87 non cat 325i's went better than my 2 post 87 cat 325i's ? But then I read somewhere that the compression was slightly adjusted on the M20 after 87 so perhaps it has more to do with that?
Also if the cat has been removed in a 1989 325 do they still test the emissions to cat standard? Or if you inform the tester that it's been removed do they test to a lower standard?
Thanks

[Bob_S]

I'm interested in this process also.
I like Brian's idea of removing the cat the old fashion way, (smashing with a pipe).
Brian, I have a 2 piece system, does the front section have to be removed from the car to remove the bits of smashed cat, Just seems a hassle removing the front exhaust section on a 2 piece. Is it possible to lift the front to get most of the cat out? I have a new rear section ready to go on and was going to cut the cat out, but leaving the pipe there and smashing the cat out seems a simpler and quicker approach!
I would have thought there must be a few BHP to be had on a 325 by removing the cat. My only evidence for this is that my 2 pre 87 non cat 325i's went better than my 2 post 87 cat 325i's ? But then I read somewhere that the compression was slightly adjusted on the M20 after 87 so perhaps it has more to do with that?
Also if the cat has been removed in a 1989 325 do they still test the emissions to cat standard? Or if you inform the tester that it's been removed do they test to a lower standard?
Thanks

do you definately have a cat? it's rare that e30's had them..

[monkey]

do you definately have a cat? it's rare that e30's had them..
_________________

. i have hade 4 318is's and none have had a cat ,nor any of the other ones that i have seen . did they even fit them to the IS ?

[Chris-W]

Yep, they did. It was a requested option, though, so understandably rare.

[k10]

Not 100 % sure until I start the job. I thought all 325'is after 88 had them??

[Chris-W]

No, not at all.

[Bob_S]

nope was a £400 option, only late uk spec M3's had them according to bmw sales brochure as standard

[Gibson]

my bloody 320i se has a cat.... silly fecker that put that on there needs shooting! luckily im finding he had some other nice options put on it so it kinda makes up....

[Bob_S]

my bloody 320i se has a cat.... silly fecker that put that on there needs shooting! luckily im finding he had some other nice options put on it so it kinda makes up....

bss325i has a good b25

and ise's came with a lot of options anyway

[Gibson]

my bloody 320i se has a cat.... silly fecker that put that on there needs shooting! luckily im finding he had some other nice options put on it so it kinda makes up....

bss325i has a good b25

and ise's came with a lot of options anyway

yea im trying to see if i can scrape the money together for that engine... i got laid off about a month ago and things are beginning to get a bit tight but i really want that engine!

yea i need to go to bm and find out what was SE stuff and what was optional stuff

[Bob_S]

ise on a late 320 was

skirts, dechrome, 13but obc, colour coding, different int trim in comfort, rear pop outs, elec roof, headlight washers and intensive wash

[Gibson]

well i have rear boot lining and tool kit (i thought that was standard on all saloons but someone told me its not) leather, 2 tone dash, Cat, Business stereo, rear feet heaters and some other little touches i cant remember now

[Bob_S]

yeah boot lining, interior light delay, tool kit is standard someone is chatting bullshite, 2 tone was stock too forogt about that, leather option cat option, stereo option, dunno about rear heaters.. thought it was quattro porte only?

[Brianmoooore]

nope was a £400 option, only late uk spec M3's had them according to bmw sales brochure as standard

Plenty of late tourings had compulsory cats!

[Bob_S]

my bad forgot about post 92 tourings, that would mean late cabs have them too?