de-cat or not de-cat

[mr.oogieboogie]

hello everyone,

bit of a follow up to the which exhaust for my s4 post. after speaking to a company (dont want to mention the name, but car has got super sport silencer on from them) i have been told to keep the cat on my s4, although that is obvisiouly my decision so any ideas as to which will be best as i'm now a bit confused as what to do. i was going to get a de-cat pipe to fit and leave the larini until later next year.

so any pros and cons would be greatful

all the best

[Tentenths]

You realise that if you do de-cat you'll have to refit it every year to get it through the MOT?

At the risk of adding to your confusion have you considered a high flow sports cat?

[mr.oogieboogie]

yes i know that it is a requirement for an mot. have fitted a few exhausts so cant see it being much of a problem apart from usual siezed bolts etc.

[Advantage]

Cons first: It'll be louder (see pros). You'll need to re-fit it every MOT time. You'll be killing 12 baby penguins every mile you drive. You'll fail any roadside emissions testing (and have to re-fit, then present the car at an MOT place)

Pros: It'll be louder (see cons). It'll allow the turbo to spool up a fraction earlier. It'll liberate at least 2, yes 2, bhp more (but seat of the pants will tell you 20 bhp). Your precious catalyst won't be wearing out while sitting on a shelf in the garage. You'll get flames on the overrun (this is a good thing).

Personally, I'm saving the environment by not wearing out my catalytic converter prematurely and necessitating the production of a replacement.

[mr.oogieboogie]

not too keen on penguins, (prefer kitkat's) wonder why people say you get 15bhp extra ifits only 2?. a bit more noise will be good

[neal]

not too keen on penguins, (prefer kitkat's) wonder why people say you a bit more noise will be good

Regarding the noise, I found that on my V8 the cats didn't reduce the noise significantly. But they did change the sound noticably. With a sports exhaust or no exhaust, the cats (even sports cats) produced a much more boomy sound. Without the cats it was a crisper, cleaner sound and you could really hear the whine from the turbos (very cool).

But beware of your insurance. In my case the cats had been blown out, but I still had the cat casings in place so I could claim it was wear and tear and they were fine at the last MOT. But if you fit a decat pipe it will be obvious that you've deliberately made the vehicle unroadworthy which is almost certainly an exclusion in your insurance policy. Also, you can't declare it as a mod since it is technically illegal.

How old/many miles is your existing cat? If it's on it's last legs you could just hollow it out and buy a new one for the MOT.

Edited December 3, 2007 by neal

[arbell9]

I had my GT3 decatted for a while whilst it (the CAT) was being refurbished.

On peformance, I would say it had better throttle response, on noise bugger all difference with the stock silencer.

Now I have a CAT + larini system. The throttle response is sharper again, seems to gallop faster....... but that could be in my mind in the same way I believe that angelina jolie thinks of me when doing brad pitt.

And it is definitely louder, even 5 esprits back! Small children and animals wet their pants with fear at the rumble and OAPs call the council asking if I qualify for an ASBO.

My money is on get the exhaust changed, keep that CAT. Saves farting about changing them at MOT time.

Alex

[Quicker]

IMHO - save the money on the de-cat pipe and hollow out your existing cat if there is any sign of deterioration to the inner honeycomb. You'll need a new cat anyway to pass MOT and that's where you should spend the money - get the high-flow one and then you can decide to leave it on when you re-fit it next year for MOT testing.

I was surprised to find a few chunks of cat honeycomb in my exhaust when I swapped out the muffler - so I took a flashlight I found that the entire cat was gone - hollow. I passed emissions only 1000 miles ago - so I do not think I lost the whole cat over the last 1000 miles, but since I passed - either the car can pass without a cat or it just blew out.

Edited December 3, 2007 by Quikr

[neal]

IMHO - save the money on the de-cat pipe and hollow out your existing cat if there is any sign of deterioration to the inner honeycomb. You'll need a new cat anyway to pass MOT and that's where you should spend the money - get the high-flow one and then you can decide to leave it on when you re-fit it next year for MOT testing.

I was surprised to find a few chunks of cat honeycomb in my exhaust when I swapped out the muffler - so I took a flashlight I found that the entire cat was gone - hollow. I passed emissions only 1000 miles ago - so I do not think I lost the whole cat over the last 1000 miles, but since I passed - either the car can pass without a cat or it just blew out.

Cats are very fragile. Once the honeycomb structure fractures, it loses all structural intergrity and will just blow apart eventually.

If you did decide to hollow out the cat, one option would be to just whack the monolith with a piece of wood using a hammer so it fractures and then let if fall apart. If there's lots of drill of chisel marks on the inside of the casing then it would be more obvious that it was deliberate.

[mr.oogieboogie]

thanks for the tip, it was m.o.t ed in october so the emissions should be fine (hopefully for next year) looks like the larini with the cat left on.

all the best

[davegtst]

Don't know if its different on an esprit but on my skyline removing the cat gained me 18 bhp. This was proven on a dyno.

[rens914]

thanks for the tip, it was m.o.t ed in october so the emissions should be fine (hopefully for next year) looks like the larini with the cat left on.

all the best

No cat (straight flow pipe) and Larini

no big problems with the annual test (MOT)

do have to tangle a bit with the vacuum but it;'s worth it

i pass every year because for the vieuwers the cat is still there (its only empty with a connecting pipe run trough).

perhaps the fact that my son does the MOT helps too. but if he gets a inspection it has to be OK

he states it is.

you could also have yourself welded a straight flow pipe.

yust change it once a year only for the mot (1 hours work x 2)

somebody handy can make one in a few hours (for little money)

you wont believe the roar you'll get

rens

Edited December 3, 2007 by rens914

[Riddlemr2]

I had Foreign Toys in Fort Lauderdale, FL de-cat my S4. They punch out the catalyst and weld a steel pipe in the canister so there is no visual evidence that the cat is actually non-functional. The car sounds much better, and there was a noticable increase in power. Living in a state without inspections, I don't have to worry about getting it tested but I do harbor some environmental guilt. I drive an Acura Integra every day which gets 34 miles/gallon so I don't feel so bad

[Paul93Lotus]

I had Foreign Toys in Fort Lauderdale, FL de-cat my S4. They punch out the catalyst and weld a steel pipe in the canister so there is no visual evidence that the cat is actually non-functional. The car sounds much better, and there was a noticable increase in power. Living in a state without inspections, I don't have to worry about getting it tested but I do harbor some environmental guilt. I drive an Acura Integra every day which gets 34 miles/gallon so I don't feel so bad

Also remember that if you decide to sell your car almost all other states have emissions testing of some type and it will make it difficult to sell without having a cat ready to go in there.

[rens914]

Also remember that if you decide to sell your car almost all other states have emissions testing of some type and it will make it difficult to sell without having a cat ready to go in there.

i think that's the problem of the guy buying my car

rens

[ragingfool35]

I decated for more noise and gone none

just got unwanted backfiring

that cat did not look restrictive

I have magnaflow exhaust

anyway, will be adding a magnaflow hi-flo cat sometime