CATs

When I chaged the exhaust I noticed a lot of external corrosion on my catalyctic converter. As the car recently passed the emmission test for the MOT I presume it's still working ok but I thought I would look into replacing it. As usual this leads to questions:

My exhaust came with the extra 90 degree piece to fit my straight CAT. This has the hole for the extra Lambda sensor that I don't have on a Mk 1 and has a sealing bolt in place.

I notice that the later CATs which have the 90 degree turn are over twice the price of the straight one I would need but I could use either now. So is there any performance difference between the 2 CATs and, if not, wouldn't it be more economical to fit a 90 degree pipe and buy a straight CAT if you have a later model? That way the next CAT replacement would be substantially less money.

What are the benefits of geting a 'sports' CAT, or a CAT bypass and are these legal?

How long does a CAT last?

Thnaks.

Laz1957 wrote: When I chaged the exhaust I noticed a lot of external corrosion on my catalyctic converter. As the car recently passed the emmission test for the MOT I presume it's still working ok but I thought I would look into replacing it. As usual this leads to questions:

My exhaust came with the extra 90 degree piece to fit my straight CAT. This has the hole for the extra Lambda sensor that I don't have on a Mk 1 and has a sealing bolt in place.

I notice that the later CATs which have the 90 degree turn are over twice the price of the straight one I would need but I could use either now. So is there any performance difference between the 2 CATs and, if not, wouldn't it be more economical to fit a 90 degree pipe and buy a straight CAT if you have a later model? That way the next CAT replacement would be substantially less money.

What are the benefits of geting a 'sports' CAT, or a CAT bypass and are these legal?

How long does a CAT last?

Thnaks.

I've just done that ie using a mk1 cat with a stainless 90degree bend adapter. to our Mk2 MGF. Saving a good few quid.

A sports cat is basically a freer flowing cat with less active material, and some struggle to pass the MOT emission with it.

A cat bypass is illegal for cars manufactured after 1993/4...

My cat was the original, so had lasted 10 years...

Thanks for that David, that was what I thought but I wanted confirmation.

So does the sports CAT deCAT give substantially better performance, exhaust tone?

Laz1957 wrote: Thanks for that David, that was what I thought but I wanted confirmation.

So does the sports CAT deCAT give substantially better performance, exhaust tone?

It makes the exhaust louder and does, in theory, allow better gas flow, so could give some performance improvement.

a sports cat or de cat will give better performance and the exhaust is a little better,but to be honest you wouldnt notice it.but the second lamba sensor on some tf cars will give a high reading if the cat is removed and this will effect engine managment so you could go into limp mode

you have to bear in mind its only a 1.8 and the exhaust system wasnt that bad from the factory,remember mg wanted to to the best they could.even with a sports exhaust you gain 5 bhp at most.2.5 bhp at the wheels.its best to fit a new cat.sports exhaust.and if your car has done more then 60,000 miles new injectors,you car loses 5. bhp every 10,000 miles of it life.

dazlightyear wrote: a sports cat or de cat will give better performance and the exhaust is a little better,but to be honest you wouldnt notice it.but the second lamba sensor on some tf cars will give a high reading if the cat is removed and this will effect engine managment so you could go into limp mode

The post CAT lamda sensor isn't used by the ECU to adjust ignition or fueling though? It it my understanding it is only to monitor emmisions and will only illuminate the dash MIL if the CO2 is above a certain threshold. If it did effect fueling, those that fit decats and thus fit a MIL illiminator loom would be driving around in limp-home mode no?

Kameleon wrote:

dazlightyear wrote: a sports cat or de cat will give better performance and the exhaust is a little better,but to be honest you wouldnt notice it.but the second lamba sensor on some tf cars will give a high reading if the cat is removed and this will effect engine managment so you could go into limp mode

The post CAT lamda sensor isn't used by the ECU to adjust ignition or fueling though? It it my understanding it is only to monitor emmisions and will only illuminate the dash MIL if the CO2 is above a certain threshold. If it did effect fueling, those that fit decats and thus fit a MIL illiminator loom would be driving around in limp-home mode no?

You are correct.

The pre cat sensor is responsible for fuelling etc and the post cat is indication only.

Also, anyone buying a new cat needs to know that if your car was registered from1st March 2001 onwards (Y Reg) you will need to purchase a type approved cat. In fact it is illegal for a shop to sell you one.

This doesn't effect most F's, but worth noting.

Some MK1 vehicles (made for Japanese export) had a cat with a sensor hole farthest from the engine, not for a lambda but for a temperature sensor "pencil". Overheating at this point caused a light to come on in the dash, but that's all, just a warning.
These cat's are available, but more expensive and not required. Just take out the sensor pencil and strap it up out the way.

Jeff

cjj wrote:

Kameleon wrote:

dazlightyear wrote: a sports cat or de cat will give better performance and the exhaust is a little better,but to be honest you wouldnt notice it.but the second lamba sensor on some tf cars will give a high reading if the cat is removed and this will effect engine managment so you could go into limp mode

The post CAT lamda sensor isn't used by the ECU to adjust ignition or fueling though? It it my understanding it is only to monitor emmisions and will only illuminate the dash MIL if the CO2 is above a certain threshold. If it did effect fueling, those that fit decats and thus fit a MIL illiminator loom would be driving around in limp-home mode no?

You are correct.

The pre cat sensor is responsible for fuelling etc and the post cat is indication only.

Also, anyone buying a new cat needs to know that if your car was registered from1st March 2001 onwards (Y Reg) you will need to purchase a type approved cat. In fact it is illegal for a shop to sell you one.

This doesn't effect most F's, but worth noting.

Even though it is illegal there are still places doing it when I replaced the cat on my previous N reg f about 2 years ago I was able to buy one without giving registration details the same seller on ebay still does not insist on you providing your reg and this is a company that sell hundreds a week. We have no shortage of laws what we dont have is the means or the will to enforce them. when my current car needed a new cat even though it came out of the factory with a non type approved cat it was y registerd so I decided to do the right thing and pay twice as much to be legal. I have read that the type approved ones are better made and will consequently last longer though I would be very intrested to know if any body or organisation has ever cut one of each in half to confirm they are signifigantly different or whether were just being forced to pay extra for a stamp on the cat and a nice certificate because our European overlords like to throw there weight about because at the end of the day providing our cars pass the emmisions test on the MOT why should it matter

midlife martyr wrote: ..............when my current car needed a new cat even though it came out of the factory with a non type approved cat it was y registerd so I decided to do the right thing and pay twice as much to be legal......

On a Y reg you would have proberbly been ok with a non type approved one as the car may well have been manufactured before the regulation came into force.



I've not tested this but IIRC the F runs worse with no cat than it does with a sports or standard cat.

Yes but I should imagine the regulations work on date registered and manufactureres are allowed a fair bit of leeway as cars can be manufactured in some cases years before there registered for example for work I run a mk1 Octavia tdi the mk2 were launched in 2005 yet the mk1s were still available to taxi companies up till 2010