de-cat pipe

[low 16v]

iv got a 1.8 16v on an L reg itsa got a full Magnex system from the cat back and its pritty loud but iv heard a de-cat pipe will make it louder and up performance. I also read in fast car about a 19 16v with a de-cat pipe that popped and done flames.

Has ne 1 got 1 or seen one what did they think ne help cos i dont wanna get one if they aint ne good?

cheers all!

 

[RobFenn]

is it a performance cat or a straight pipe? Remember your car wont pass the MOT if you remove the cat!

 

[DTWD]

RobFenn is correct, anything after J reg will not pass without a CAT. You will get better performance without one because there is a less restriced airflow out of the car. But you need to get the ECU altered to take account of the lack of CAT as it will probably go mad. The CAT wont be sending information back to the ECU and so it will bugger up the running of your car. Unless there is something on DECAT pipes that tell the ECU not to care or give it the perfect results it wants. But I think you need a chip.



Paul

 

[Siggsy]

Ive got a Magnex full system with de-cat pipe havent had it chiped yet and its runnin fine!

Want to at some stage tho where abouts is Hill Power??

 

[RobFenn]

So, siggsy, are u gonna put the cat back on at MOT or what?

K-tec are better than hillpower!!

 

[adiclio16v]

it wont mess up the ecu cos the lambda sensor is before the cat, ive got 1 and mine runs fine you just have to swap it at MOT time its only 4 bolts

worth getting the fuelling checked as it might be running a bit lean a chip will sort this

adi

 

[Steveold]

It should effect the ecu as the there will be no back pressure etc and the lamda sensor is not designed for that.......

 

[big hp]

Cut off point was 93 (k) i think you will find.

Ill find out for sure tonight my mate is a MOT tester.

Scott

 

[low 16v]

i aint worried about the MOT i can replace the cat for that i just wondered if it would run ok or if the ECU would play up, so far iv heard different things i think ill ask when i get buy it,.

i wanna get it chipped so if it does play up it will be a good reason to get it done i spose.

Ne 1 know about popping or flames rally style so iv heard any clues on that one?

 

[RobFenn]

erm yeah get a new ecu and set it up to overfuel, hence more unburnt fuel which will get burnt of at the exit = flames.

Pops and bangs tend to be reserved to turbod cars..but my dads db7 vantage did it so there most be something going on which i obviously dont know about.

 

[RobFenn]

R-tec have a flamer kit where u can press a button which will do the flames thing by the way, you will still need it to be overfuelling though and to be honest, bit tacky.

 

[Siggsy]

Yer SCC do one aswell.. all it is is a Spark plug in the exhaust so excess fuel ignites.....

 

[clio_racer]

So... worth another set-up after a de-cat? Im running k-tecs silenced item on my RT and it was running a bit (understatement) rich before and seems to be the same now... Whether it pops is fueling based... mine sounds gorgeous but the economy is suffering for it. Taking it to anything over 3000 RPM and then backing off gives a gorgeous rally kind of popping... Maybe does need setting up... Im gonna miss that noise

Advice?

 

[RobFenn]

You havent got a V8 for gods sake! Fuel economy cant be that bad can it? Get a second job!!

 

[low 16v]

thats the popping i was talking about i didnt want a flamer kit, it was just a bonus if it pops cos dare i say it (my nova done it and i miss it) SORRY.

As long as performance is up and it runs ok ill go for it cos moneys tight and i cant afford a chip yet!

 

[adiclio16v]

mine pops flames wen giving it some, its quite cool, unfortunately you cant see it and it doesnt do it all the time

adi

 

[low 16v]

has your car got anything else done to the engine apart from the exhaust and de-cat pipe?

 

[RobFenn]

So basically if i set my car to overfuel it will do the old pops and bangs?

Surely adi your clio lets out flames when your not giving some, i.e when you lift off the accelerator?

 

[adiclio16v]

yeh it does it on overrun when you back off the accelerator but you have to be at high revs to get flames when you back off

also helps if the exhuast is hot pops and bangs more wen its hot too

my car is standard apart from the de-cat full mongoose and piperx induction kit, it may be overfueling slightly i dont know, chip will be going in soon

adi

 

[Bryan]

just to clear a point here

above it mentions from various people that a car will not pass the MOT if it doesnt have a cat fitted, this is not true. The car will only fail the MOT if the exhaust emissions do not meet the legal limitations, having a cat helps the car meet these limits

i know this because i had a de-cat pipe on my Saxo VTR in addition to a full magnex system and it passed its MOT at Citroen (only just), hope this helps clear the subject

 

[BenR]

how do you kow flames come out if your in the car?

and the little grumbly poppity pops happen on almost all cars when silencers are removed and you have a slightly lean idle.

 

[Nick Read]

OK just to clear everything up:

MOT - doesnt matter whether youve got a cat or not, but on post-91 cars, cats were standard and emissions regs tighter. If your car can still pass the emissions test without a cat then no worries. If it cant, either get a bent ticket or stick the cat back on for the test.

As I learnt from the oracle BenR many moons ago, popping etc will happen if the air/fuel ratio is wrong, either too rich OR too lean. Either way there will be unburnt fuel entering the exhaust. If the system is hot enough, it will pop. If there is a straight and easy enough path to the tailpipe and enough unburnt fuel, you will get flames.

The Magnex decat will not make the system any louder than it already is, at least thats my experience. Its a proper silencer. A straight through pipe will make the system louder because youre losing the cat and its silencing effect.

The lack of a cat makes absolutely no difference to the lambda sensor whatsoever. It still reads oxygen content in the gas flowing past it, just the same as always, and it is before the cat pipe anyway.

Back pressure will decrease slightly with a decat pipe, not enough to make any drastic chipping necessary, youll just have better exhaust flow out of the engine. Chipping will help to bring together a range of basic mods, eg. decat, freer flowing exhaust system, induction mods; but its not necessary just for a decat job.

 

[BenR]

hehe....im gonna get piccky for a min.......

the poppetty pop noise on overrun is almost purely from a lean idle mixture.

as you run down off throttle, not all teh carge is burn due to inefficiencies such as ignition timing (little of) little gas flow etc etc. thsi nburn fuel passes thorugh the exhaust and builds up on the glass pack in silencers and when the quantity is large enough, burns off with teh heat of teh exhast alone....with a mild pop.

fora rich mixture to burn, a source of ignition is needed (of which our exhausts are not hot enough) adn will result in a huge BANG, not pop. however, there are always exceptions, but im not saying this is a rule. BTW, i run my carbs lean on idle....hehe

 

[adiclio16v]

i know flames come out of my exhaust cos several people have told me after being behind my car

adi

 

[BenR]

that would be a good answer...haha

 

[DTWD]

The flames and pops that come courtasy of rally cars are a bi-product of the over fueling they put on there cars to get the engine hotter quicker...or at least thats what I remember Prodrive saying. But they also said it doing that creates loads of pollution. So I would watch your next MOT if it pops and flames.



Thanks Nick for clearing it all up. My local MOT inspector told me after 91 you had to have a CAT. So thats where I got that from. As for the chipping I had been told that some peoples cars run very poorly after getting a decat. So I assumed this was something to do with the sensors. Sorry for my misinformation.



Paul

 

[RobFenn]

So how many silencers are on my car? (mk3 clio) and can i get them removed and stil pass the MOT.

I think ill ask my dealer if it will pass without a cat.

Thanks for the great responses guys, very interesting! Makes my membership definetly worthwile!!

 

[adiclio16v]

i was under the impression there are too differant emissions tests one for cat cars and one without

but after 91 you would have to have a cat anyway so would automatically take the stricter test

if your car is 1990 say and has a cat you have to take the stricter test but if you take it off you go down to the lower figure test

if your car is after 91 you need the cat back on anyway so wether it causes more pollution now or not i dont really care

please correct me if im wrong cos im not completely sure

adi

 

[RobFenn]

Id go with that Adi, i thought it was mandatory to have CATS on 2. Maybe the bloke testing BAMBAMs saxo presumed the CAT was there and didnt check!

 

[BRUN]

nope Adi, it doesnt matter

mines a 1992 K and because it wasnt a 93 K i got tested as though no cat was needed

 

[adiclio16v]

i thought the year was after 92 but further up the page sum1 said it was 91 so i thought id go wiv that

btw i dont know if the cat is not there on a car after 91-2 (whatever the yr is) if the mot inspector sees its not there he can fail you anyway

but your car might still pass the stricter test anyway so ud be alright if he doesnt notice

adi

 

[RobFenn]

sweet..in that case ill be asking k-tec for a de-cat pipe

 

[Will16V]

So if i replaced the cat with a de-cat pipe on my 95 16V, it would just be on the emissions, if they were low enough to pass the M.O.T?

 

[RobFenn]

Ive emailed K-tec asking about this Will. But if anyone knows before i get a reply..

 

[RobFenn]

From David at K-tec

Hello, we do not have a de cat pipe for the 1.2 16v yet and you can pass an MOT without a cat if the emissions are OK. Normal de cat pipes will not allow you to pss an MOT.

David.

 

[adiclio16v]

ok so there is two differant tests one needs lower emisions than other BUT

if your car is before 92 and has a cat it takes the lower em test but you can remove it and it will then be allowed higher em and take the other test

cars after 92 have to take the lower em test anyway regardless of having a cat or not (there must be some cars after 92 that wasnt fitted with cats from new)

most cars after removing the cat will not have low enough emissions to pass the lower emissions test so will fail on that

 

[DTWD]

I would have thought that if you got your car setup properly (for performance) then its not going to like you putting the cat back on. Even if it is just for an hour or so. Surely its going to do something nasty. But I dont know.

I dont know about the year thing either, but I was told anything AFTER J reg needed a cat. What do KTEC mean by saying:

"Normal de cat pipes will not allow you to pss an MOT."

What do they mean by that? What are normal and un-normal decat pipes? any ideas?



Paul

 

[Bryan]

no ideas, but im content that any car can pass an MOT without a cat fitted as long as the emissions are within the legal limit

 

[RobFenn]

well performance cats could be un-normal?? Maybe thats what david meant