de-cat

[nizmainiac]

just wondering if it's worth de-catting my e34 or not , as the cat rules on mot don't apply until 1992 and mine was made in 1989

[Alexlind123]

Sure, you will probably get more power especially at higher RPMs.

[hatched91]

i was wondering the same. i was thinking remove my cat, and replace my tri-flow muffler with a borla muffler, but leave the resonators and piping in from the tri-flow cat-back. i think w/o a cat it'll give it more air-flow and with the borla muffler, it'll give it a more throaty sound. whenever you hear that distinctive sound of a mustang cobra that is super loud and very throaty, it's borla. about 30 of them are around my area that i see and hear daily. but what about the computer? will it still run okay?

[BigKriss]

What does the computer have anthing to do with the cat. The o2 sensor is before the cat - you will have no problems.


i was wondering the same. i was thinking remove my cat, and replace my tri-flow muffler with a borla muffler, but leave the resonators and piping in from the tri-flow cat-back. i think w/o a cat it'll give it more air-flow and with the borla muffler, it'll give it a more throaty sound. whenever you hear that distinctive sound of a mustang cobra that is super loud and very throaty, it's borla. about 30 of them are around my area that i see and hear daily. but what about the computer? will it still run okay?

[nizmainiac]

i'd forgotten i'd asked this, good to know it can be done with no ill after effects

[bmw_ryder]

i've detached my cat from my e34 and putted an sport muffler,the sound is great,and with this modification i think i've obtained till 5hp.
the cat is an part that need to be changed in time,but few people know that.
mine was broken

[nizmainiac]

yeah i know . i've changed a fair few of them in my time

[hatched91]

yeah i didn't look under the vehicle before i asked, i know some have precat and aftercat or just after cat. i think i'l talk to a few muffler shops to get a price quote. i'd like to go with no cat and a borla muffler. that means b&b tri-flow muffler will be up for grabs soon.

[hatched91]

yeah got to looking and you're going to need two long pipes that are bent and what not, my guess around $100 at a shop. i want to go y pipe after the downtubes to a 2.5" pipe all the way back to a borla muffler. does anyone know if it's better to have the muffler at the end or have a tailipipe with a tip?

[hatched91]

okay, went and had the cat cut out. cost be about $60. one pipe was 3' long and the other was 3.5' long. i have a cat-back b&b tri-flow exhaust and it really sounds like garbage, but then again there are a couple of exhaust leaks. i have 2.25 piping back. i believe if i can sell the cat-back exhaust, i can have true dual exhaust run with two glass-back style borla mufflers. i believe that will give me a much throatier tone.

[hatched91]

oh, and the o2 sensor is in the center of the cat, not before, as for now my check engine light is on until i drill and tap the o2 sensor in.

[Alexlind123]

oh, and the o2 sensor is in the center of the cat, not before, as for now my check engine light is on until i drill and tap the o2 sensor in.

On my 1990 535i, the O2 sensor is right before the cats...........

[hatched91]

well here's a pic of my 1990 535i cat http://img116.imageshack.us/img116/391/0000400fq8.th.jpg (http://img116.imageshack.us/my.php?image=0000400fq8.jpg)
http://img83.imageshack.us/img83/4105/0000400va0.jpg (http://imageshack.us)

[genphreak]

well here's a pic of my 1990 535i cat
http://img83.imageshack.us/img83/4105/0000400va0.jpg (http://imageshack.us)The cats are in the fat bit. The section the sensor is mounted in is in is the X-pipe section. I forgot they have this... seen mine lots of times.

Best to make sure whatever you replace it with is stainless as it still gets hella hot here. If I de-catted mine it'd be 50mm pipes all the way from the engine pipe ends (or the manifolds themselves). The less joins the better- but it has to go on and come off easily and not rattle and shake- BMW designed some give into the system at certain points to handle engine movement and the odd hit on the tailpipes, etc.

[rob101]

i have a stuffed cat, I am never even going to consider getting a decat. the smell of the exhaust is terrible not to mention the poisious things like CO and NOx that you can't smell.

[hatched91]

i'ts definitally stainless. don't notice any smells but i do have a nasty exhaust leak where the cat-back bolts up. i don't think the gasket is there.