De-catted my car today

kazul

Whipped off my catalytic convertor today and replaced it with a straight through pipe. Power gains are modest but it revs more freely and is quieter now. I just have to wait to see what happens with fuel consumption.
Has anybody else gotten rid of their cat? If so, what was the result?

dudara

Saw the thread title and was going to reply about getting my mother's six ginger moggies off the bonnet of my car. Cat hair still stuck to my car after doing 2 hours on a motorway.

Not quite the same meaning as you had

Henry Ford III

How will the NCT people view this?

kazul

They will view it with the catalytic convertor back on in 2012

kazul

dudara wrote: »

Saw the thread title and was going to reply about getting my mother's six ginger moggies off the bonnet of my car. Cat hair still stuck to my car after doing 2 hours on a motorway.

Not quite the same meaning as you had

I actually gutted an old cat which sounds even more gruesome. Looks the same from outside but there's no honeycomb inside, piped straight thru instead.

dirtydiesel

My car needs a new cat and I was thinking of doing the same, did you make a pipe to fit or is there a bypass pipe available, my car is a saab 900, whats yours.

breadmonkey

Is this legal?

if it was a diesel no one would ever know

bmstuff

breadmonkey wrote: »

Is this legal?

Depends what year is the car
I think it was made mandatory back in 2000. so earlier cars can remove it if they want. I stand corrected...

vectra

bmstuff wrote: »

Depends what year is the car
I think it was made mandatory back in 2000. so earlier cars can remove it if they want. I stand corrected...

Interesting

Midnight_EG

OP what car is it?



I put a test pipe on my Civic on Thursday, it's more responsive and the noise is orgasmic

bmstuff

bmstuff wrote: »

Depends what year is the car
I think it was made mandatory back in 2000. so earlier cars can remove it if they want. I stand corrected...

The vast majority of pre 2000 petrol cars made in the 90s won't have a hope of passing an NCT emissions test without a working cat.

Anan1

Wouldn't you have to retune the engine to get the full benefit of removing the cat? AFAIK it's not just the back-pressure (modern cats are fairly free-flowing) it's the fact that the fuel/air mixture is metered to suit the cat rather than for maximum power.

kazul

It's a '98 Cefiro (jap spec Maxima) 2.0 v6.
Who cares if it's legal or not, how will they find out?
I got a 2nd hand CAT to get it thru the first NCT so I had the old one as spare. I knocked out the "puddings" with an iron bar an welded in a 54mm pipe so it still looks like a CAT is fitted.
We used to have an exhaust and tyre centre in the early 90s and the old man says the first Opels with CATs were a bit of a disaster and he used this "cure" on them for an Opel dealer for warranty work.
My lamda sensor is "upwind" of the CAT and the car knows no different.
I just need to pop my K&N filter back in, the spurious exhaust system was a making a "boomy" note that I didn't like and I put in an original air filter in case the K&N was contributing with induction noise.
There are differing opinions on what effect the change will have on fuel consumption...

Anan1

kazul wrote: »

My lamda sensor is "upwind" of the CAT and the car knows no different.

Wouldn't it still be adjusting mixture to suit the now absent cat?

kazul

If it can't tell if a CAT is present or not why would it adjust? The reason for doing it was to help exhaust gases flow freer.
AFAIK it also has 2 pre-cats on the downpipes. The major test was whether the engine management light came on. It didn't and the car performs marginally better.

Anybody want to buy some platinum?

Henry Ford III

What about your civic responsibility/carbon foorprint?

Matt Simis

RoverJames wrote: »

The vast majority of pre 2000 petrol cars made in the 90s won't have a hope of passing an NCT emissions test without a working cat.

Thats not quite correct. Any 1993 and earlier car doesnt not need a Cat to pass an NCT. On the legality question earlier, there is no law here prohibiting removal of Cats (NCT pass or not aside), unlike the US.

Anan1 wrote: »

Wouldn't you have to retune the engine to get the full benefit of removing the cat? AFAIK it's not just the back-pressure (modern cats are fairly free-flowing) it's the fact that the fuel/air mixture is metered to suit the cat rather than for maximum power.

Ideally for full benefit yes, but generally you will always get some benefit unless the engine is highly tuned for back pressure (typically smaller engines afaik).

Anan1 wrote: »

Wouldn't it still be adjusting mixture to suit the now absent cat?

What do you mean, the "real" O2 Sensor(s) monitors oxygen in the exhaust, the MAF monitors Airflow on the input. Both of these continue to work fine after removal of the Cat.

In OBD2 cars, there is an additional headache with the rear of Cat (or close by to Cat) O2 Sensor which is there is try detect an emissions fault (and not monitor engine performance), these are the ones that people use the steel bungs on to move them further out of the exhaust flow to trick them (and therefore the ECU) into thinking the Cat is still present.

kazul

The catalysing process changes carbon monoxide (CO) to carbon dioxide (CO2) and reduces hydrocarbons slightly.
I couldn't give a tinker's curse about my "carbon footprint", that whole global warming, carbon offsetting thing is horse****e IMO

Anan1

kazul wrote: »

If it can't tell if a CAT is present or not why would it adjust?

Because it can't tell?;) I'm no engineer, but my guess is that you'll get a marginally more free-flowing exhaust by removing the cat but that the real benefits would require a remap. Otherwise your engine is still behaving as if it has a cat.

kazul

Anan1 wrote: »

Because it can't tell?;) I'm no engineer, but my guess is that you'll get a marginally more free-flowing exhaust by removing the cat but that the real benefits would require a remap. Otherwise your engine is still behaving as if it has a cat.

Remap is not gonna happen, engine/ecu is OBD1 AFAIK. And it's not marginally more free-flowing, it's way more free-flowing. I want the engine to behave like it should, i.e. combust fuel in the most efficient and powerful way possible and send said power to my wheels via the transmission.

And I was bored and wanted to do a mod that cost me nothing and gave me the opportunity to get down and dirty.

Matt Simis

Matt Simis wrote: »

Thats not quite correct. Any 1993 and earlier car doesnt not need a Cat to pass an NCT. .

I know, if it was't for the different emissions test for pre 94 cars I would have said practically all 90s petrol cars wouldn't have a hope of passing an NCT rather than saying the vast majority

ShadowHearth

cat long time gone in my one.... ill be back for nct thought

SouperComputer

Anan1 wrote: »

Because it can't tell?;) I'm no engineer, but my guess is that you'll get a marginally more free-flowing exhaust by removing the cat but that the real benefits would require a remap. Otherwise your engine is still behaving as if it has a cat.

Nope, no need for a remap. There's a range that the ECU operates over. Fuel trim being the main one invloved here (arguably advance could be tweaked too, but the difference would be teeny compared to fuel trim). A cat removal is well within the fuel trim adjustment of any ECU.

Matt Simis

Anan1 wrote: »

Because it can't tell?;) I'm no engineer, but my guess is that you'll get a marginally more free-flowing exhaust by removing the cat but that the real benefits would require a remap. Otherwise your engine is still behaving as if it has a cat.

I think you are looking at this in too digital a manner.
Engines are mechanical beasts, if the exhaust gases vent faster then it will have an effect on performance, either positive or negative, depending on its existing design.

The dyno I did showed a 10bhp gain over stock, Im putting this down largely to the De-Cat. It also clearly Revs faster now too. Im told with a Remap that takes this into account I could get a total of 30bhp increase (thats general remap tuning and the decat).

Ive completely decatted a couple of cars (and removed the downpipe cats in another). Consistently shown performance gain:
http://www.youtube.com/watch?v=ghYOeUcej9c
http://www.youtube.com/watch?v=r1Xu_XIZNpY

i.need.a.job

eats fuel

Midnight_EG

i.need.a.job wrote: »

eats fuel

Anything to back this claim up?


I hear it makes fuel consumption better!

rugbyman

am pleased to read that someone is being "inventive". Am surprised that the "Thoughtpolice" who urge "report your neighbour for not paying VRt " and reort tax dodgers are not here yet!

Regards ,Rugbyman

unkel

kazul wrote: »

It's a '98 Cefiro (jap spec Maxima) 2.0 v6.

Big slow heavy saloon with about 140BHP? Why bother de-catting the car? It's not like you are going to notice any performance differences, is it?

i.need.a.job

Midnight_EG wrote: »

Anything to back this claim up?


I hear it makes fuel consumption better!

friend decatted his golf, said there was a noticable difference

Midnight_EG

i.need.a.job wrote: »

friend decatted his golf, said there was a noticable difference

So you have no real proof then.

kazul

unkel wrote: »

Big slow heavy saloon with about 140BHP? Why bother de-catting the car? It's not like you are going to notice any performance differences, is it?

Why not? Didn't take long, didn't cost anything.

Matt Simis

i.need.a.job wrote: »

friend decatted his golf, said there was a noticable difference

DeCats generally improve economy, they did for me every time. Your friend probably liked the sound of his exhaust more (loud pedal over use).

Anan1

Matt Simis wrote: »

I think you are looking at this in too digital a manner.
Engines are mechanical beasts, if the exhaust gases vent faster then it will have an effect on performance, either positive or negative, depending on its existing design.

The dyno I did showed a 10bhp gain over stock, Im putting this down largely to the De-Cat. It also clearly Revs faster now too. Im told with a Remap that takes this into account I could get a total of 30bhp increase (thats general remap tuning and the decat)

That's my point - removing the cat may improve performance by reducing back-pressure, but the engine won't be making the most of it. For 10bhp I wouldn't be bothered, when a proper remap could give me so much more without the hassle of changing setup for the NCT.

.Longshanks.

I was going to buy a replacement downpipe for my car from thorney motorsport in the UK (one with without the pre-cat) and decided to ring the insurance company just to be sure everything was 100%. The replacement downpipe would have given me 5-7 extra bhp & make the exhaust pop & bang a bit more when changing up under high rev's.
Turned out it was going to make my insurance double! They would then class my car as a modified motor so didn't bother in end up.
....& the part would only have cost me about €70!

guil

Midnight_EG wrote: »

Anything to back this claim up?


I hear it makes fuel consumption better!

wheni i had a impreza, i had a decat downpipe and blitz nurspec r exhaust and blitz induction kit

no word of a lie i used to go through €250:eek: a week on petrol, i drove to work from newbridge to carlow everyday and around a bit at the weekend
it was loud as fcuk

stimpson

RoverJames wrote: »

The vast majority of pre 2000 petrol cars made in the 90s won't have a hope of passing an NCT emissions test without a working cat.

Nonsense. My old 91 CRX had a decat pipe. It always flew the NCT emissions test. More power, freer reving and reduced fuel consumption.

I wouldn't recommend gutting a cat as someone has suggested - they are full of carcinogens and other nasty things.

I t is possible to get a high-flow cat that will reduce the back pressure while still being legal.

Henry Ford III

stimpson wrote: »

Nonsense. My old 91 CRX had a decat pipe. It always flew the NCT emissions test. More power, freer reving and reduced fuel consumption.

I wouldn't recommend gutting a cat as someone has suggested - they are full of carcinogens and other nasty things....

Why are cats factory fitted then?

I'd have assumed that if they didn't serve a useful purpose the manufacturers would not have bothered fitting them. They are not cheap.

stimpson

Henry Ford III wrote: »

Why are cats factory fitted then?

I'd have assumed that if they didn't serve a useful purpose the manufacturers would not have bothered fitting them. They are not cheap.

They do reduce emissions and they are a legal requirement. Pre 93 cars do have different limits admittedly but my baby was still a fraction of the limit.

A regularly serviced car should have no problem passing without a cat. Jap and German cars anyway.

bmstuff

Anan1 wrote: »

That's my point - removing the cat may improve performance by reducing back-pressure, but the engine won't be making the most of it. For 10bhp I wouldn't be bothered, when a proper remap could give me so much more without the hassle of changing setup for the NCT.

Depends of the car really, if you do that with some, you will lose lots of power, while with others, it will increase power.

bmstuff

Henry Ford III wrote: »

Why are cats factory fitted then?

I'd have assumed that if they didn't serve a useful purpose the manufacturers would not have bothered fitting them. They are not cheap.

Because manufacturers knew about the incoming legislation.
It is like OBD2 cars, they were in before it was made mandatory.

Manufacturers do not wait for legislation to come into force to start adapting cars to the new piece of law.

JHMEG

Your "carbon footprint" is measured in terms of CO2 emissions. CO2 is a harmless gas. Ironically removing your cat reduces your carbon footprint, but increases your emissions of CO, a highly toxic gas. Emissions of NOx also increase, again highly toxic and corrosive.

Cats have nothing to do with carbon footprint. They're there for human health reasons.

stimpson

stimpson wrote: »

Nonsense. My old 91 CRX had a decat pipe. It always flew the NCT emissions test. More power, freer reving and reduced fuel consumption.

I wouldn't recommend gutting a cat as someone has suggested - they are full of carcinogens and other nasty things.

I t is possible to get a high-flow cat that will reduce the back pressure while still being legal.

I said vast majority, you gave an example of a 91 car and state nonsense, well done. As mentioned on the thread pre 93 cars have a much easier emissions test to pass than post 93. Decat any post 93 petrol car and see how your NCT goes, then come back here and let us know how it went.

stimpson

<snip>

stimpson

RoverJames wrote: »

I said vast majority, you gave an example of a 91 car and state nonsense, well done. As mentioned on the thread pre 93 cars have a much easier emissions test to pass than post 93. Decat any post 93 petrol car and see how your NCT goes, then come back here and let us know how it went.

I'm just stating facts. You were spouting nonsense with your uninformed opinion presented as fact. Perhaps it's true of most Rovers

Just checked my nct cert - .29% CO2 (max 3.5%). That's with well over 100,000 miles on the engine. The post 93 limit is 0.6%, so it would have flown that too.


I still reckon most cars in a good state of tune would fly it without a cat.

Matt Simis

Anan1 wrote: »

That's my point - removing the cat may improve performance by reducing back-pressure, but the engine won't be making the most of it. For 10bhp I wouldn't be bothered, when a proper remap could give me so much more without the hassle of changing setup for the NCT.

On a NA car a 10bhp increase is huge and it isnt a sure bet that a remap would give more. Besides, I wouldnt advocate this on a newer car unless it had a mega turbo that would clearly benefit from less backpressure. Usually removing the pre-cat is enough, its only there for cold start emission testing, which is not performed here (or most places) and is detrimental to turbo lifespan and overall performance.

stimpson

stimpson wrote: »

I still reckon most cars in a good state of tune would fly it without a cat.

Any one who has had to buy a cat to pass an NCT since it came in would disagree

Barr

Decatted my old FTO and added a K&N filter , two weeks later I restored it back as the fuel economy plummeted.

stimpson

RoverJames wrote: »

Any one who has had to buy a cat to pass an NCT since it came in would disagree

That's hardly the vast majority of pre-2000 cars.

stimpson

Barr wrote: »

Decatted my old FTO and added a K&N filter , two weeks later I restored it back as the fuel economy plummeted.

If the FTO has a cat sensor then it can run in open loop mode when it's missing which will kill your efficiency. I used a 1K resistor on the CRX to fool the ECU into thinking the CAT was still there.

stimpson

stimpson wrote: »

That's hardly the vast majority of pre-2000 cars.

It's a representation, if what you say is true no one would need to buy a cat at all.