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My rear silencer is a bit rusty, so figure I should replace the whole exhaust. Wanted to get a ragazzon dual exit but theyre 400? + 400? shipping. Will probably get a custom one made.

Are there any benefits of doing this? Will the turbo behave better or worse? Or should I get a whole exhaust made with a catalytic converter?

Not really expecting power gains, just looking to do something for my car, if it will help the car breathe more.

Engine is a 81kw from a 156, swapped into a 147.
 

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I have a 2005 156 JTDM 150 ( remapped to about 190), and I needed a new exhaust at 110,000 ( on the original !) so I opted for a Cybox stainless steel single exit system with a decat ( the 'cat' is just a small 'silencer' ). I actually took the car down to The Wirral from Co Durham to have it fitted at the factory workshop. I was very impressed with the service, and it looks great. I must admit that I was a little disappointed in that I expected it to be a bit louder than standard (!) but that aside, there was no noticeable increase in power or mpg. So I am not sure that it actually does affect the engine performance..... However, I wanted a stainless system and IIRC ( it was a couple of years ago now ) it cost about £320 fitted. That was a good deal, especially compared to an Alfa OEM system !
 

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Discussion Starter #3
Would you say there is a benefit to doing that, or should I just replace the rusty rear silencer? I just want a bit more grunty sound, if thats possible with such an exhaust.

Also, does anyone know if the exhaust made for a 8v jtd will fit a 16v engine? And if not, can the part connected to the manifold simply be replaced without touching the rest? Was thinking of swapping in a 16v eventually.b
 

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I my case, I decided that I would need a whole system as it had done 10 years/100,000 miles on the original one....including 2 track days at Croft Race circuit ! I am sure that Cybox could have made the system louder if I had asked them, but I did not know how it was going to sound until it was finished ! Also, I intended to keep the car and could see no reason to get an OEM complete system as it would have been a lot more expensive ( IIRC in 2013)

By the way, on my previous Alfa 156 1.8TS, I managed to buy a secondhand Cybox back box via on of the Alfa forums, and I was so impressed with that one that I went with them for the diesel one. The TS engine did sound so good with that S/H box on, a bit louder but not too loud, so I was looking forward to the same difference with the JTDM fitment...

So if you are going to keep the car I would get it done, otherwise maybe try and source a used one ?
 

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Discussion Starter #5
I my case, I decided that I would need a whole system as it had done 10 years/100,000 miles on the original one....including 2 track days at Croft Race circuit ! I am sure that Cybox could have made the system louder if I had asked them, but I did not know how it was going to sound until it was finished ! Also, I intended to keep the car and could see no reason to get an OEM complete system as it would have been a lot more expensive ( IIRC in 2013)

By the way, on my previous Alfa 156 1.8TS, I managed to buy a secondhand Cybox back box via on of the Alfa forums, and I was so impressed with that one that I went with them for the diesel one. The TS engine did sound so good with that S/H box on, a bit louder but not too loud, so I was looking forward to the same difference with the JTDM fitment...

So if you are going to keep the car I would get it done, otherwise maybe try and source a used one ?
Was looking previously at a few used ones, but the car culture here is so basic and weird. Replacing the exhaust just means replacing the rear silencer, or even just the tip to make it sporty-looking. Definitely no complete exhausts for sale. Even so, my engine seems to be very rare - 81kw from 156. Upon some digging around, found out it was only made during 2001. It's a bit of a hassle when looking for parts, because I have to explain everyone that the car is a 147 but the engine is from the 156.
 

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Hi. My car is straight piped from the turbo all the way to the back. What I can say,well , it's mostly benefits. When idling, it sounds deeper, it has some grunt to it, it's miles better than a stock exhaust. It presumably sounds great at speed ,but I haven't really heard it from the outside, I have been told so.

Negatives...well the lack of any cat means the gasses go straight to the back and sometimes at a stop light, with windows down, I can start smelling the diesel being burned. It's not a leak anywhere ,it's just from the exhaust. I've checked numerous times and have talked to people ,who share the same modification with the same results.
 

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==sorry, wrong section==
Hi Guys,
Just a quick question. I have 159 2,4 210cv. DPF-off, EGR-off, remaped to theoretical 243hp/470nm. Now thinking about decat (mostly to get deeper exhaust tone). Do I still need to make software changes if DPF allready off? Whats better - remove internals of CAT (You can actually sell those for about 100EUR/pce) or straight downpipe?
Thanks!
 

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This should be in the 159 Brera section, but no you wont need any remap, the probe is just a temperature sensor. I removed the internals of the cat on my 1.9159, I did notice the turbo spooled up quicker. A proper pipe would be better than an empty cat as the gas will flow much more smoothly than when going into a larger chamber and then back out again.
Iwas thinking about doing the same to my 2.4 Brera but heard from a well thought of tuner that it can cause turbo overspeed issues.
 

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My rear silencer is a bit rusty, so figure I should replace the whole exhaust. Wanted to get a ragazzon dual exit but theyre 400? + 400? shipping. Will probably get a custom one made.

Are there any benefits of doing this? Will the turbo behave better or worse? Or should I get a whole exhaust made with a catalytic converter?

Not really expecting power gains, just looking to do something for my car, if it will help the car breathe more.

Engine is a 81kw from a 156, swapped into a 147.
Contrary to popular belief, de-catting wont really give you any benefits, maybe literally a couple of BHP more, the only thing it will do is make your car spew out more crap into the air that you and the rest of us have to breathe.

the 'cat' is just a small 'silencer' !
No - there are 2 "cats" the first (under the bonnet) is actually a heat sink that keeps the exhaust gases warm to enable the catalytic process that change some of the harmful exhaust gases in the second (middle) cat into less harmfull gases (heat helps the process), the third (the last one, at the back of the car) box is a silencer.
 

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Discussion Starter #10
Contrary to popular belief, de-catting wont really give you any benefits, maybe literally a couple of BHP more, the only thing it will do is make your car spew out more crap into the air that you and the rest of us have to breathe.



No - there are 2 "cats" the first (under the bonnet) is actually a heat sink that keeps the exhaust gases warm to enable the catalytic process that change some of the harmful exhaust gases in the second (middle) cat into less harmfull gases (heat helps the process), the third (the last one, at the back of the car) box is a silencer.
I completely get what you mean. I don't even like the sound of a de-cat diesel. It sounds very unnatural and weird. And decatting would be a hassle since I would either have to bribe the inspections guy (which is easy) or I'd have to re-fit it everytime I have to get it insured.

But I was figuring why not do it if I'm getting a complete exhaust.

May just get the rear silencer, tho, since the original one is rusty. Would just a rear silencer deepen the sound at all? No HP gains, obviously, but at least the sound?
 

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I completely get what you mean. I don't even like the sound of a de-cat diesel. It sounds very unnatural and weird. And decatting would be a hassle since I would either have to bribe the inspections guy (which is easy) or I'd have to re-fit it everytime I have to get it insured.

But I was figuring why not do it if I'm getting a complete exhaust.

May just get the rear silencer, tho, since the original one is rusty. Would just a rear silencer deepen the sound at all? No HP gains, obviously, but at least the sound?
You can fit a complete new and bigger exhaust and still keep the cat, opening up the entry and exits to the same size as the new exhaust, or use a cat from a diesel with a bigger exhaust, or fit an uprated "sports cat".

You can get a very small increase in power with a freer flowing/larger diameter silencer or you can remove it altogether - a lot of people who fit new exhausts to their JTDs on here do and say that its barely any louder. You can buy silencers that deepen the sound too.

(shameless plug - I m selling one in the classifieds).
 

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Worth saying that all this depends on the level of boost you are runnning..

If the boost is high and thd exhaust diameter or flow is not up to the job you will get very high egt's leading to the ecu reducing fuelling..

The result

Flatspots at high boost..

There ard a couple of ways around it..a freer flowing exhaust and cat removal being one..

The other ways are too reduce the temp of the charged air...so either a fmic or water meth.

If you are running normal boost then I think the pre cat is the only one worth removing as it will help with earlier turbo spool.

Main cat leave it in place...unless of course you are running very higb boost(3 bar)
 

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Its here : Alfa Romeo Classifieds - Auctions - Tuning - Powered by PhotoPost Classifieds

Worth saying that all this depends on the level of boost you are runnning..

If the boost is high and thd exhaust diameter or flow is not up to the job you will get very high egt's leading to the ecu reducing fuelling..

The result

Flatspots at high boost..

There ard a couple of ways around it..a freer flowing exhaust and cat removal being one..

The other ways are too reduce the temp of the charged air...so either a fmic or water meth.

If you are running normal boost then I think the pre cat is the only one worth removing as it will help with earlier turbo spool.

Main cat leave it in place...unless of course you are running very higb boost(3 bar)
You can simply fit a larger cat to the freer flowing exhaust, a 3" one for instance.

147, 156 and GT JTDs already have an FMIC, I think you mean a bigger and/or relocated FMIC. :)
 

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Thanks for answer guys. What do You mean by main cat? As I said DPF is already empty - straight pipe welded inside) Now thinking about cat that comes right after turbo:
see attached - 04.4184.
Main reason is to get deeper tone (as some of members here said that after decat it sounds more deeper) and quicker spool.
I have booked those jobs for this wednesday together with new turbo, i will let You know the results :)
 

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Thanks for answer guys. What do You mean by main cat? As I said DPF is already empty - straight pipe welded inside) Now thinking about cat that comes right after turbo:
see attached - 04.4184.
Main reason is to get deeper tone (as some of members here said that after decat it sounds more deeper) and quicker spool.
I have booked those jobs for this wednesday together with new turbo, i will let You know the results :)
The main cat is the one under the car, the first "cat" is not a cat but a heat sink.
 

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The main cat is the one under the car, the first "cat" is not a cat but a heat sink.
That definitely is a cat up front.. It's positioned close to the engine so that it catches the exhaust whilst it' still hot, especially important on a cold start since the rest of the exhaust is stone cold!

Cats work when warm - main cat takes time to warm up, but once warm will work well because it's nice and big!

The small one up from will reach operating much more quickly because it's both smaller, and closer to the engine - but it's small, and won't work as well as the main cat at full load.

Combine the above with he fact that the ECU over-fuels the engine when it's running cold to deliberately warm things up more quickly, and you have much worse tailpipe emissions directly after a start-up.. Downpipe cat is installed to take a bit out of those start up emissions, but not at all required when running at temperature.
 

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You can simply fit a larger cat to the freer flowing exhaust, a 3" one for instance.

147, 156 and GT JTDs already have an FMIC, I think you mean a bigger and/or relocated FMIC. :)

If we are being pedantic then yes all of the 1.9 JTD cars have an intercooler but I would say its more ''side mount'' being stuck on the right in front of the N/S wheel...its not exactly in the optimum position for airflow ....

so my definition of a front mounted intercooler is centrally located and of course bigger...I found at states of tune up to 225 ish BHP EGT are not hugely an issue so after running briefly with an FMIC I elected to keep stock as I don't use the car for track days so its not on high boost for long periods...between Damien and myself we have discovered a lot as both cars were hybrid turbo'd and mapped within months of each other and we both have had gradual increases in power over a period of about a year...obviously things have been learnt along the way.

Damien's is in a higher state of tune for sure but we came to the same conclusions and solutions at pretty much every step if the way...our % increases over stock are exactly the same as we started with a 20hp difference and ended up with a 20hp difference...

my point is I am not giving you an opinion I am giving you facts based on the very exhaustive tuning of two 1.9 JTDm's, mine a blackline 150 and Damien,s a clover 170

once I got the 250 map it was obvious at WOT in some situations the EGT's are too high and it was proven to be down to the flow of the gasses out of the tailpipe as flat spots are much reduced after the fitting of a straight through pipe in addition to the de-cat down pipe.

the flat spots are still very slightly evident but I have yet to make a decision on what to to do about it and TBH it doesn't affect the performance in 90% of situations..that said I am likely to go water meth injection over a larger and more suitably placed intercooler as I would like to keep my induction piping length stock...mime are stainless steel and cost a few quid so I am inclined to keep them.

so as I stated earlier in terms of removing the main cat you will very likely notice no difference at the state of tune possible on a CF3 engine in terms of actual power, sound will be different ,whether the resulting change in that is considered an improvement will be down to taste.


30hp is yours with just a decent remap , much more than 190-200hp will require a modified/bigger turbo and the required clutch,fly gearbox an brake mods to handle/harness it.


get the map and see how you feel..


certainly no need to do it all at once!
 

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That definitely is a cat up front.. It's positioned close to the engine so that it catches the exhaust whilst it' still hot, especially important on a cold start since the rest of the exhaust is stone cold!

Cats work when warm - main cat takes time to warm up, but once warm will work well because it's nice and big!

The small one up from will reach operating much more quickly because it's both smaller, and closer to the engine - but it's small, and won't work as well as the main cat at full load.

Combine the above with he fact that the ECU over-fuels the engine when it's running cold to deliberately warm things up more quickly, and you have much worse tailpipe emissions directly after a start-up.. Downpipe cat is installed to take a bit out of those start up emissions, but not at all required when running at temperature.
Where have you found this out ? - I ve done a fair bit of research and the best I could come up with was that its something to get the cat up to temp rather than an actual cat, although what I found out didnt verify it 100%.

If you read my earlier post your ll see that I know that cats work best when warm and its for this reason that I said its a heat sink - to get the main cat up to temperature. Indeed, this set up is not used on more modern diesels - most now have close coupled integrated cats/DPFs (and sometimes NOx traps) right next to the exhaust manifold in the same position as the first cat on our cars, precisely because this is a warm area.

I m also aware that the ECU over fuels initially

We both agree its for heat, whether it actually contains any precious metals that initiate catalytic reactions is where we disagree. I havent been able to verify it is an actual cat and If you look inside it your ll see that it doesnt really have the amount of surface area youd expect from an actual cat.

Happy to admit I m wrong and it DOES contains precious metals, if you can point me towards something that proves it :)

If we are being pedantic then yes all of the 1.9 JTD cars have an intercooler but I would say its more ''side mount'' being stuck on the right in front of the N/S wheel...its not exactly in the optimum position for airflow ....

so my definition of a front mounted intercooler is centrally located and of course bigger...I found at states of tune up to 225 ish BHP EGT are not hugely an issue so after running briefly with an FMIC I elected to keep stock as I don't use the car for track days so its not on high boost for long periods...between Damien and myself we have discovered a lot as both cars were hybrid turbo'd and mapped within months of each other and we both have had gradual increases in power over a period of about a year...obviously things have been learnt along the way.

Damien's is in a higher state of tune for sure but we came to the same conclusions and solutions at pretty much every step if the way...our % increases over stock are exactly the same as we started with a 20hp difference and ended up with a 20hp difference...

my point is I am not giving you an opinion I am giving you facts based on the very exhaustive tuning of two 1.9 JTDm's, mine a blackline 150 and Damien,s a clover 170

once I got the 250 map it was obvious at WOT in some situations the EGT's are too high and it was proven to be down to the flow of the gasses out of the tailpipe as flat spots are much reduced after the fitting of a straight through pipe in addition to the de-cat down pipe.

the flat spots are still very slightly evident but I have yet to make a decision on what to to do about it and TBH it doesn't affect the performance in 90% of situations..that said I am likely to go water meth injection over a larger and more suitably placed intercooler as I would like to keep my induction piping length stock...mime are stainless steel and cost a few quid so I am inclined to keep them.

so as I stated earlier in terms of removing the main cat you will very likely notice no difference at the state of tune possible on a CF3 engine in terms of actual power, sound will be different ,whether the resulting change in that is considered an improvement will be down to taste.


30hp is yours with just a decent remap , much more than 190-200hp will require a modified/bigger turbo and the required clutch,fly gearbox an brake mods to handle/harness it.


get the map and see how you feel..


certainly no need to do it all at once!


ALL JTDs have intercoolers 1.9 and 2.4. Its not pedantic - no cars have side mounted intercoolers, well no front engined cars anyway. The OEM cooler is on the front of the car and therefore is an FMIC, its not the biggest and the ducting is not the best - it could certainly do with bigger holes in the bumper, but theres nothing wrong with its front mounted location. As long as its on the front it doesnt matter whether its to the left, to the right or in the centre, its an FMIC. You wouldnt say that the head light is "side mounted" cos it isnt and neither is the OEM IC. :)

I m very familiar with your thoughts/experiences with ICs, indeed we share the same opinions on the ridiculously long pipework needed for fitting a larger intercooler in front of the rad. But there is a lot of BS talked about intercoolers and every single aftermarket install I ve seen on here is running intake temps approx 10% higher than they should be simply because they havent been installed correctly.

Like most of the forum, I m familiar with your and Damiens cars, what 1.9 JTD engines are capable of and what is necessary to handle it all, having done many of these mods to several cars already, although modifying the flywheel is not "required", its entirely optional. 225 is achievable WITHOUT a bigger turbo and of course many more people have gone the bigger turbo route, rather than the hybrid route, which can see up to 310PS.

All I was saying is that removing the cat wont give much of a power increase and that the sorts of power levels mentioned above ARE achievable WITH a cat, as many production and motorsport cars prove (Audi won LeMans 8 or 9 times ALWAYS with FULL emissions equipment). When I can afford a new turbo it will be a GTB2056v, GTB2260v or similar and I will DEFFO be keeping my emissions equipment. :)
 

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Where have you found this out ? - I ve done a fair bit of research and the best I could come up with was that its something to get the cat up to temp rather than an actual cat, although what I found out didnt verify it 100%.

If you read my earlier post your ll see that I know that cats work best when warm and its for this reason that I said its a heat sink - to get the main cat up to temperature. Indeed, this set up is not used on more modern diesels - most now have close coupled integrated cats/DPFs (and sometimes NOx traps) right next to the exhaust manifold in the same position as the first cat on our cars, precisely because this is a warm area.

I m also aware that the ECU over fuels initially

We both agree its for heat, whether it actually contains any precious metals that initiate catalytic reactions is where we disagree. I havent been able to verify it is an actual cat and If you look inside it your ll see that it doesnt really have the amount of surface area youd expect from an actual cat.

Happy to admit I m wrong and it DOES contains precious metals, if you can point me towards something that proves it :)
I've always thought it was a cat and referred to it as a cat or pre-cat.

Judging by the amounts that metal merchants have previously paid me for them from breakers (they have a book with OEM part numbers and the equivalent 'class' of catalyst) I would say they certainly have some precious metals in there, but nowhere near as much as the main cat. As a rule the main cats have always tended to be worth 4 or 5 times more than the pre-cats.

ePer also refers to it as "silencer catalyzed". I'm fairly confident there is at least some precious metals in there.
 

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