Leon Cupra ST stock rear muffler modification

[Juusoavk]

Evening! I have acquired a stock Leon Cupra ST catback which I want to modify to get a louder exhaust. I have now opened the rear mufflers and the insides look like these. What would you guys do to the piping? I'm thinking about doing it like it is in the Golf R variant, so otherwise an straight pipe but it has a slit in the middle chamber inside the muffler. Might be hard to weld that in though. I'm not looking for a complete straight pipe, but would like something louder like the Golf R for example.

 

[Bruper24]

Evening! I have acquired a stock Leon Cupra ST catback which I want to modify to get a louder exhaust. I have now opened the rear mufflers and the insides look like these. What would you guys do to the piping? I'm thinking about doing it like it is in the Golf R variant, so otherwise an straight pipe but it has a slit in the middle chamber inside the muffler. Might be hard to weld that in though. I'm not looking for a complete straight pipe, but would like something louder like the Golf R for example.View attachment 43265View attachment 43263View attachment 43264View attachment 43262

What did you end up doing? Do you have a video of the sound?

 

[nd-photo.nl]

Always interesting to see these kind of pictures

 

[Juusoavk]

What did you end up doing? Do you have a video of the sound?

It took two iterations in the end. First I removed the perforated inlet pipe with crimped end, made large holes in the first baffle and welded plates in the last baffle which contains the wool. This had very minimal effect on the sound and I wasn't satisfied with it.



I opened the mufflers again and followed how some other people on this forum had done, by leaving a small space between the inlet and outlet pipes. I believe this is how it is in the stock Golf R estate by the pictures I found. The final modification only required 1 new 45 degree stainless pipe if I remember correctly, all other pieces were scavenged from the insides that were removed. The piping is sized such that they fit inside or outside each other, which helps with the welding. This modification was actually much easier to do and I should have maybe done so from the start Removing the first baffle completely makes it easier to work inside and doesn't make the structure weak.



Sound is very similar inside to stock during normal driving and no drone at all. I think that the modifications only affect when driving more aggressively and when the revs are higher. The DSG sounds are now heard in Sport/Cupra mode, where they were barely audible even from outside before. I have left the resonator untouched. I will post a video a bit later.

 

[nd-photo.nl]

Thanks for posting an update and more pictures

 

[Bruper24]

It took two iterations in the end. First I removed the perforated inlet pipe with crimped end, made large holes in the first baffle and welded plates in the last baffle which contains the wool. This had very minimal effect on the sound and I wasn't satisfied with it.

View attachment 48496View attachment 48497View attachment 48498

I opened the mufflers again and followed how some other people on this forum had done, by leaving a small space between the inlet and outlet pipes. I believe this is how it is in the stock Golf R estate by the pictures I found. The final modification only required 1 new 45 degree stainless pipe if I remember correctly, all other pieces were scavenged from the insides that were removed. The piping is sized such that they fit inside or outside each other, which helps with the welding. This modification was actually much easier to do and I should have maybe done so from the start Removing the first baffle completely makes it easier to work inside and doesn't make the structure weak.

View attachment 48499View attachment 48500

Sound is very similar inside to stock during normal driving and no drone at all. I think that the modifications only affect when driving more aggressively and when the revs are higher. The DSG sounds are now heard in Sport/Cupra mode, where they were barely audible even from outside before. I have left the resonator untouched. I will post a video a bit later.

Thanks for the update!
The inlet and outlet pipes seem very very close to each other, so I’m surprised you say there is no difference when driving normal.

Very curious about the sound.

my idea is to put a valve just before the muffler and connect it to the outlet inside the muffler, so I can have stock sound and louder. I haven’t seen an exhaust that accomplishes this for sale yet.

 

[Juusoavk]

Thanks for the update!
The inlet and outlet pipes seem very very close to each other, so I’m surprised you say there is no difference when driving normal.

Very curious about the sound.

my idea is to put a valve just before the muffler and connect it to the outlet inside the muffler, so I can have stock sound and louder. I haven’t seen an exhaust that accomplishes this for sale yet.

That is definitely a cool idea. With the way the original pipes are very close to each other in the stock Cupra muffler, I think that making the bypass pipe will be tricky. Are you planning on keeping it looking like stock from underneath? There are also some DIY mufflers with this kind of functionality available.

I thought that I had done a lot of modifications when I had done the first modifications and the mufflers were shut, but when I drove with it I couldn't tell a difference to stock. Now in the final state that they are in I was surprised that it isn't louder. Before I started doing anything I did a lot of research on the topic and people with backbox deletes would say that that drone, but the setup I have has no drone though the pipes inside the muffler are close. All in all, how comparable from the inside it is to stock during casual driving surprised me as well. Have you seen this thread, there is a lot of information available too like a video from another member with the same modification. I tried to find a video of mine where I accelerate, but couldn't find one from a standstill, I need to go record one

 

[nd-photo.nl]

@Juusoavk thanks for sharing this info!

 

[Bruper24]

That is definitely a cool idea. With the way the original pipes are very close to each other in the stock Cupra muffler, I think that making the bypass pipe will be tricky. Are you planning on keeping it looking like stock from underneath? There are also some DIY mufflers with this kind of functionality available.

I thought that I had done a lot of modifications when I had done the first modifications and the mufflers were shut, but when I drove with it I couldn't tell a difference to stock. Now in the final state that they are in I was surprised that it isn't louder. Before I started doing anything I did a lot of research on the topic and people with backbox deletes would say that that drone, but the setup I have has no drone though the pipes inside the muffler are close. All in all, how comparable from the inside it is to stock during casual driving surprised me as well. Have you seen this thread, there is a lot of information available too like a video from another member with the same modification. I tried to find a video of mine where I accelerate, but couldn't find one from a standstill, I need to go record one

To answer with your own picture.
My idea is to add a valve just before the each muffler. The pipe from the valve when open, should go towards as close to the tip as possible.
There is less back pressure in this tube, so I expect most of the air to deviate from the back box into this.

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[nd-photo.nl]

Why not just do a cutout? Its less of a hassle. I have a cutout before it splits to the mufflers. In the meantime I added a 90 degree turn, so that it exits the rear of the car instead of the side

(dont mind the rust, will be resolved with new arms)

 

[Juusoavk]

To answer with your own picture.
My idea is to add a valve just before the each muffler. The pipe from the valve when open, should go towards as close to the tip as possible.
There is less back pressure in this tube, so I expect most of the air to deviate from the back box into this.
View attachment 48518


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I see. In my opinion this seems quite complicated and propably wont result in much of any change like what I experienced with my first iteration, due to still some going through the other path.

 

[Juusoavk]

Why not just do a cutout? Its less of a hassle. I have a cutout before it splits to the mufflers. In the meantime I added a 90 degree turn, so that it exits the rear of the car instead of the side

(dont mind the rust, will be resolved with new arms)

Hurricane exhaust has kind of the same style where with valve closed the exhaust goes through a muffler only on the other side and with valve open the other side is a straight pipe https://www.hurricane-exhaust.de/klappenabgasanlagen/seat/leon-cupra/. Don't know if the stock piping is large enough to have everything go out one side if the goal is to keep stock mufflers.

How much does this setup drone when the cutout is under the car? Would be interesting to compare how the Golf R style modified mufflers are quieter compared to this.

 

[nd-photo.nl]

With the 90 degree added, it was a big reduction. The sound is now "thrown" to the back of the car, instead of staying under the car. It has little drone with low rpm in D-mode, but with spirited driving in S-mode, its virtually zero.

Hurricane is a cool setup, but costs 3k without even installing it Guy I know has a Hurricane system paired to a BullX downpipe with HJS cat, its proper loud (too much for me personally)

 

[Juusoavk]

With the 90 degree added, it was a big reduction. The sound is now "thrown" to the back of the car, instead of staying under the car. It has little drone with low rpm in D-mode, but with spirited driving in S-mode, its virtually zero.

Hurricane is a cool setup, but costs 3k without even installing it Guy I know has a Hurricane system paired to a BullX downpipe with HJS cat, its proper loud (too much for me personally)

Yeah it was just something to think about if Bruper wants to modify the stock exhaust by adding valves. Having the cutout in the middle of the pipe is definitely the easiest way to go, just like you have it.

I've been thinking how much would the sound of my setup be affected if the resonator would be removed or replaced with some smaller resonator. I've driven Audi TT 2.0 TFSI with remus exhaust and it had a nice deep tone to it, which might be impossible to achieve with modifying the stock Cupra exhaust. Goal of mine was also to keep the exhaust looking stock from under the car and saving money

 

[Bruper24]

Yeah it was just something to think about if Bruper wants to modify the stock exhaust by adding valves. Having the cutout in the middle of the pipe is definitely the easiest way to go, just like you have it.

I've been thinking how much would the sound of my setup be affected if the resonator would be removed or replaced with some smaller resonator. I've driven Audi TT 2.0 TFSI with remus exhaust and it had a nice deep tone to it, which might be impossible to achieve with modifying the stock Cupra exhaust. Goal of mine was also to keep the exhaust looking stock from under the car and saving money

It is an option, but not one I want. I rather keep the original exhaust to having only one exhaust tip working, but that is me .


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[nd-photo.nl]

The muffler and internal design plays a major role in the shape of the sound as far as I know, I think this is often overlooked.

And also "loud" is often mistaken as having a good sound shape/tone of the exhaust.

@Bruper24 a bypass is the best (looking) option if you also want the exhaust gases to leave the exhaust tips. Its a good idea to go valved with the police crackdown on loud exhausts in our country. Thats also why I kept the stock catback in stock form and only changed the tips. The cutout gives me flexibility to add sound at the push of a button.

 

[Juusoavk]

The muffler and internal design plays a major role in the shape of the sound as far as I know, I think this is often overlooked.

And also "loud" is often mistaken as having a good sound shape/tone of the exhaust.

@Bruper24 a bypass is the best (looking) option if you also want the exhaust gases to leave the exhaust tips. Its a good idea to go valved with the police crackdown on loud exhausts in our country. Thats also why I kept the stock catback in stock form and only changed the tips. The cutout gives me flexibility to add sound at the push of a button.

I tried to look for all kinds of remus etc. performance exhaust manufacturers muffler designs but seems that not many people cut open those mufflers Propably they are also selected or made to a specific car or engine in a way to muffle the unwanted frequencies and keep for example the deeper tones.

I found the catback I have modified for sale on Facebook, so I have the one that came in the car as a spare if it would have been too loud after the modifications or should I need to revert to stock for some reason.

 

[Juusoavk]

@Bruper24 Here's a video for you. Cupra mode with manual shifting, first pull is ~60% throttle and second one is wide open. Excuse the loud stabilizer of the camera creating a background noise

 

[ArchNemeziz]

This seems like the correct topic to revive for what I'm doing.

I've been obsessing over thoughts about how to convert my MY20 (double GPF model, but aftermarket DP with GPF delete) 2 tailpipe Leon Cupra ST to a 4 tailpipe version.
I have my eyes on some larger 89mm X 116mm tip face ovals which are even larger than the 105mm wide golf R quad tips. Strangely hard to find exact matches, closest I could spot which I liked were 100mm wide but the Maxton diffusor can fit more so I try to fit more
For anyone who wants to know the original tips on my ST are 135mm x 65mm

Local shop was nice enough to lend me a milltek 118 x 83 MSTIP160 since I'm sort of a regular there now. And 2 of those would fit snugly in the valence with a small gap.


The main issue is how to get them on my backboxes?
One option is get new boxes, and that's all fine and would work of course. Likely option would be a universal straight through with perforated core and a Y split inside with proper dampening filling. This would likely produce nicer sound, but until I do it I wouldn't know. Of course universal mufflers are not homolongated which means it could be a risk at technical inspection or otherwise. Keeping original look could be a benefit later so I would modify the OE boxes first to see how that works out. If cut correctly on the upper side it wouldn't be even immidiately noticable. And nobody normally really checks how many tailpipes you are supposed to have.

I've looked through probably all the exhaust discussions here and found a lot of useful feedback and images. Based on those I've been desigining my own prototype with the help of some expensive GPT license I have access to. Below is what I could come up with it so far. The goal is obviously to allow for 4 tips, but not only visually but actually functional. Without modifying the box internals the only way to do that would be an H split on the outside, but I would hate it because it would be very obvious in the winter.

Anyone got thoughts on this?
The shape is roughly accurate and the dimensions of drawn parts aren't perfect but it's close enough. I measured the inlets on the boxes at about 50mm and the outlet at 57mm and gave it a small extra measurement on the width of the box and GPT generated the rest based on images I've found. A lot of the detailed new design measurements are somewhat random numbers with "this could work" logic to fill in the idea.