sports cat

If i have a sports cat, how will my ecu respond, will it just adjust itself, envisage any problems? Will it still pass its mot, if so why dont all cats come like that?

I have a sports cat on my Saxo VTS and although its hard to tell the improvement in performance as I changed the complete exhaust system including the manifold from a 4-2-1 to a 4-1 if your revising the complete system then a free flow cat would help a little.

I've had two emission problems when it came to mot time the first turned out to be poor joins which where blowing and messing with the emissions the other turned out to be a blow from the exhaust manifold gasket.

The issue you will have is if you remove the cat completely which I have been told improves performance a great deal but at the cost of a mot failure and big increase in voloume, which is fine if thats your thing.

Price is also an issue as they aren't cheap

I removed two pre-cast on my 147 and replaced the main cat with 100 cell metalic racing cat. All lambdas are kept in place. I didnt have any issues with ECU, everything seems fine, no error codes. I will have my emissions measured in May so I will be able to compare with values from two years ago but other people with simillar setup passed without any problems.

So whats the set up with the 156? is it the same as the 147 - Pre cat - cat - centre box - back box.

I've never understood the pre-cat, is it in the manifold or just after it?

Originally Posted by 156_TSpark_Boy

So whats the set up with the 156? is it the same as the 147 - Pre cat - cat - centre box - back box.

I've never understood the pre-cat, is it in the manifold or just after it?

Depends if it's the CF2 or CF3 engines.. what year is your car? The CF3 was after 2000 IIRC.

This engine has precats and takes 4BHP off your output, giving you 140BHP instead of the earlier 144BHP.

Mines a 1.8 twinspark on a W. The first owner has fitted a Remus DTM back box which is nice on the eyes but you wouldnt know it was there in the car

If mine has a pre-cat and a cat, I might be tempted to remove the centre box to setup the volume and get the gases moving a bit more freely.

Better not tell the missis, noisy exhaust has been a touchy subjet since we meet lol

Originally Posted by 156_TSpark_Boy

Mines a 1.8 twinspark on a W. The first owner has fitted a Remus DTM back box which is nice on the eyes but you wouldnt know it was there in the car

If mine has a pre-cat and a cat, I might be tempted to remove the centre box to setup the volume and get the gases moving a bit more freely.

Better not tell the missis, noisy exhaust has been a touchy subjet since we meet lol

Haha.. my missus is the same... I'm thinking about changing the backbox on the GTA...

You also might have a center silencer which will be keeping the noise down...

Originally Posted by 156_TSpark_Boy

Mines a 1.8 twinspark on a W. The first owner has fitted a Remus DTM back box which is nice on the eyes but you wouldnt know it was there in the car

If mine has a pre-cat and a cat, I might be tempted to remove the centre box to setup the volume and get the gases moving a bit more freely.

Better not tell the missis, noisy exhaust has been a touchy subjet since we meet lol

On a W-reg yours is the 144bhp 1.8 - no precats and nice free-flowing manifolds.

You therefore have only one lambda, and it is before the cat, so its unlikely removing the cat will change the ECUs response in any way. You might gain a little bit extra power but to get most of the benefit you will need to have the car remapped.

Replacing the cat with a small silencer and replacing the centre box with a straight pipe leaves you with a very loud exhaust under load, but quiet ish on cruising. I think its the best solution myself..

Originally Posted by 156_TSpark_Boy

I've never understood the pre-cat, is it in the manifold or just after it?

They are two, in the manifold, just after the place where 4 pipes join into 2. Only the 105BHP 147 has a single pre-cat as it has 4-1 manifold instead of 4-2-1.
Pre-cats are there to lower the emissions in the initial period after a cold start as they heat-up much faster to operating temperature being so close to the engine.

my exhaust is the 2000-ish one on a 156, single cat, single lambda. it has just passed its MOT with a decat pipe fitted, so no issues at all with a sports cat. for reference, only the fast idle emissions caused an issue.

Hi guy's

have a look at my old post.mite shed some light on this.http://www.alfaowner.com/Forum/tunin...-decating.html (GTV ts exhaust mod plus decating)

regards john

Well the first owner of the car (which I'm the third and the second owner has just driven it and serviced it) changed a few things straight after leaving the factory and the Remus back box is very quiet and i can honestly see it getting a huge amount louder as european exhausts normally are more on the quieter side unlike UK aftermarket exhausts.

Like I said in another post i pick the car up this sat so once I've driven it over the weekend I'll know more about what i want to do in all areas.

Just had my pre cats removed and the main cat replaced with a sport cat.No problems at all.Sounds and responds much better Informed my insurance company, and no change to the ammount i have to pay

I think unless you putting out at least 100bhp as when I fitted a sports cat to my Saxo VTS I saw a improvement but only a slight one. Unless you was also reviseing the complete system ie cat and cat back system then it could be a waste of money. Changing the manifold is still probally the best way of improving the exhaust system imo

Ive found out that the cat in my 1.8 is just underneath the exhaust manifold, how unusal is this, do you think that will make it harder to swap for a sports cat?

As long as its in the system and not in the manifold itself a exhaust fabricator should be able to modify the pipework for you

Most sports cats work on bhp and go up in blocks of a 100 or more.

Originally Posted by Stevie28

Ive found out that the cat in my 1.8 is just underneath the exhaust manifold, how unusal is this, do you think that will make it harder to swap for a sports cat?

Not unusual at all. Since 2001.

You have precats on the manifold itself and a main cat after this.

Pre-cats in the manifold are usually very small, they are there because they heat up a lot faster than the cat in your exhaust, so work pretty much from the turn of the key. It is important for environmental reasons to have cats in the manifold, as petrol engines run very rich during the start-up phase, so lots of unburnt fuel would otherwise go straight through the main cat without burning off, because it wouldn't be up to temp.