Author Topic: New mk5 owner with lots of questions!  (Read 14506 times)

Offline OldGTI

  • Always Involved
  • ****
  • Thank You
  • -Given: 4
  • -Receive: 3
  • Posts: 63
Re: New mk5 owner with lots of questions!
« Reply #15 on: January 08, 2021, 09:40:54 AM »
Maybe someone would swap their full ome system for your straight through system? If not on here there is a few Facebook gti groups full of nutty modders?

Offline Jons1001

  • Always Involved
  • ****
  • Thank You
  • -Given: 2
  • -Receive: 0
  • Posts: 54
Re: New mk5 owner with lots of questions!
« Reply #16 on: January 08, 2021, 09:53:53 AM »
Maybe someone would swap their full ome system for your straight through system? If not on here there is a few Facebook gti groups full of nutty modders?

Yes that's a possibility but it will still cost me £250 to revert map to stock,plus £180 to fit and I will have lost 60bhp. Suppose it will sort the loudness out though, and thinking about it this is probably one of the cheaper options! Looking at the backbox though it looks original so maybe it is original from cat back then either has decat/sports cat downpipe. Do you know if a mechanic will be able to tell me if the cat has been knocked out just by looking or will they needed to take it off? Will hopefully be able to get the garage to take some photos and I will post up here exactly what's under there.

Offline brian_badonde

  • Just Arrived
  • **
  • Thank You
  • -Given: 1
  • -Receive: 2
  • Posts: 19
Re: New mk5 owner with lots of questions!
« Reply #17 on: January 08, 2021, 10:58:00 AM »
I know it passed its MOT a year ago fine but that was with the owner before the guy I bought it from. All I know is that it's been remapped and I suspect the guy I bought it from to have put a decat downpipe on when he had this done, however he told me it has a sports cat. I wouldn't be able to tell by looking myself so hoping to get a garage to look this weekend. How easy is it to tell if it has a decat, can it be done by visual inspection or will it need to be taken off to check if the cat has been knocked out?

Thanks for advice re resonator etc but as you say I need to investigate further first and I will keep the thread updated. I researched everything about maintenance etc. But overlooked the exhaust, I allowed about £500 max to sort it but I'm now a bit shocked to find out it could be more like £1500 plus! Suppose other option if it does have a decat is to try and source an OEM cat second hand and just swap for mot. Hopefully have some answers this weekend.

Yeah they're clearly visible looking at the downpipe, they're generally welded units so you'd have to cut the converter out of the housing and weld it back together which would be wholly impractical if you had to replace it each year to get it through an MOT.

Here's a picture of a downpipe with sports cat for reference:


Get under the car if you can and post some pictures from front to back of the system. Also have you got the printout of the last MOT that has lambda readings etc?

Offline Jons1001

  • Always Involved
  • ****
  • Thank You
  • -Given: 2
  • -Receive: 0
  • Posts: 54
Re: New mk5 owner with lots of questions!
« Reply #18 on: January 08, 2021, 12:14:30 PM »
Thanks, will hopefully have some photos this afternoon. Is it not the case though that sometimes decat can just look exactly the same as a cat from the outside but with the innards knocked out? I'm having trouble posting images so here is the info from mot in Jan 2020.

                      LIMIT                        READING

CO                  Max 0.20%               0.00%
HC                  Max 200 ppm            2 ppm
LAMBDA          0.97-1.03                 1.01

and on the natural idle test

C0 0.00%

I also have the remap graphs etc. not sure if that will give again clues but again i can't post the image for some reason, do you need to use a web hosting site thing? cheers

Offline brian_badonde

  • Just Arrived
  • **
  • Thank You
  • -Given: 1
  • -Receive: 2
  • Posts: 19
Re: New mk5 owner with lots of questions!
« Reply #19 on: January 08, 2021, 01:15:49 PM »
You could I guess but I can't see the point as the MOT has the emissions test which would confirm the lack of a cat regardless of whether you can visually see one or not. Best way to "cheat the system" would be to have a removable cat that you could install for an MOT once a year, why on earth people do this with road cars is beyond me but that's another topic I guess.

Lamda looks great so nothing to worry about there, don't worry about remap graphs etc. Have a look and see if you can see the cat. If so then fingers crossed it's just a case of getting it up to temperature so that it runs at a high enough efficiency to pass the emissions test. After that you've got some time to sort out a longer-term solution for your exhaust.

Offline Jons1001

  • Always Involved
  • ****
  • Thank You
  • -Given: 2
  • -Receive: 0
  • Posts: 54
Re: New mk5 owner with lots of questions!
« Reply #20 on: January 08, 2021, 01:25:48 PM »
You could I guess but I can't see the point as the MOT has the emissions test which would confirm the lack of a cat regardless of whether you can visually see one or not. Best way to "cheat the system" would be to have a removable cat that you could install for an MOT once a year, why on earth people do this with road cars is beyond me but that's another topic I guess.

Lamda looks great so nothing to worry about there, don't worry about remap graphs etc. Have a look and see if you can see the cat. If so then fingers crossed it's just a case of getting it up to temperature so that it runs at a high enough efficiency to pass the emissions test. After that you've got some time to sort out a longer-term solution for your exhaust.

Yes agreed but I was meaning more along the lines that I could check and see a cat but then not know it has the innards taken out so is in fact a decat?

Yes the lamba is good but don't forget this was the owner before the guy I bought it from. The guy I bought it from was the one who had it remapped and I'm guessing messed with the downpipe.

Offline Jons1001

  • Always Involved
  • ****
  • Thank You
  • -Given: 2
  • -Receive: 0
  • Posts: 54
Re: New mk5 owner with lots of questions!
« Reply #21 on: January 08, 2021, 04:37:03 PM »
You could I guess but I can't see the point as the MOT has the emissions test which would confirm the lack of a cat regardless of whether you can visually see one or not. Best way to "cheat the system" would be to have a removable cat that you could install for an MOT once a year, why on earth people do this with road cars is beyond me but that's another topic I guess.

Lamda looks great so nothing to worry about there, don't worry about remap graphs etc. Have a look and see if you can see the cat. If so then fingers crossed it's just a case of getting it up to temperature so that it runs at a high enough efficiency to pass the emissions test. After that you've got some time to sort out a longer-term solution for your exhaust.

Just been under and it's got a decat downpipe :-(. Then a straight pipe all the way to the rear back box (should there be a centre silencer aswell?) I have pics but not sure how to post. Guess my cheapest option now is to get a sports cat, with downpipe or weld it in? And hope it passes. Any recommendations anyone? Then there is the remapping etc. to suit sports cat, I don't mind if it loses a bit of power but obviously don't want it to damage the engine in anyway. What a headache lol

Offline brian_badonde

  • Just Arrived
  • **
  • Thank You
  • -Given: 1
  • -Receive: 2
  • Posts: 19
Re: New mk5 owner with lots of questions!
« Reply #22 on: January 08, 2021, 06:55:15 PM »


You could I guess but I can't see the point as the MOT has the emissions test which would confirm the lack of a cat regardless of whether you can visually see one or not. Best way to "cheat the system" would be to have a removable cat that you could install for an MOT once a year, why on earth people do this with road cars is beyond me but that's another topic I guess.

Lamda looks great so nothing to worry about there, don't worry about remap graphs etc. Have a look and see if you can see the cat. If so then fingers crossed it's just a case of getting it up to temperature so that it runs at a high enough efficiency to pass the emissions test. After that you've got some time to sort out a longer-term solution for your exhaust.

Just been under and it's got a decat downpipe :-(. Then a straight pipe all the way to the rear back box (should there be a centre silencer aswell?) I have pics but not sure how to post. Guess my cheapest option now is to get a sports cat, with downpipe or weld it in? And hope it passes. Any recommendations anyone? Then there is the remapping etc. to suit sports cat, I don't mind if it loses a bit of power but obviously don't want it to damage the engine in anyway. What a headache lol

Damn. What a pain in the hoop. This bloke you bought it off sounds like a trustworthy individual.

There should be a resonator too like you said, although lots of people get rid of them. That'll be another reason it's too loud for you.

It probably is the cheapest option but by the time you've added a new downpipe, resonator plus welding time you won't be far off a whole system I imagine. But worth getting a quote for maybe? Either that or scour the classifieds for a downpipe with a cat.

Don't worry about the map too much, it'll still run and won't damage the engine or anything, it just won't run as well as with a new map.

Sent from my SM-G960U using Tapatalk


Offline Jons1001

  • Always Involved
  • ****
  • Thank You
  • -Given: 2
  • -Receive: 0
  • Posts: 54
Re: New mk5 owner with lots of questions!
« Reply #23 on: January 08, 2021, 07:11:03 PM »


You could I guess but I can't see the point as the MOT has the emissions test which would confirm the lack of a cat regardless of whether you can visually see one or not. Best way to "cheat the system" would be to have a removable cat that you could install for an MOT once a year, why on earth people do this with road cars is beyond me but that's another topic I guess.

Lamda looks great so nothing to worry about there, don't worry about remap graphs etc. Have a look and see if you can see the cat. If so then fingers crossed it's just a case of getting it up to temperature so that it runs at a high enough efficiency to pass the emissions test. After that you've got some time to sort out a longer-term solution for your exhaust.

Just been under and it's got a decat downpipe :-(. Then a straight pipe all the way to the rear back box (should there be a centre silencer aswell?) I have pics but not sure how to post. Guess my cheapest option now is to get a sports cat, with downpipe or weld it in? And hope it passes. Any recommendations anyone? Then there is the remapping etc. to suit sports cat, I don't mind if it loses a bit of power but obviously don't want it to damage the engine in anyway. What a headache lol

Damn. What a pain in the hoop. This bloke you bought it off sounds like a trustworthy individual.

There should be a resonator too like you said, although lots of people get rid of them. That'll be another reason it's too loud for you.

It probably is the cheapest option but by the time you've added a new downpipe, resonator plus welding time you won't be far off a whole system I imagine. But worth getting a quote for maybe? Either that or scour the classifieds for a downpipe with a cat.

Don't worry about the map too much, it'll still run and won't damage the engine or anything, it just won't run as well as with a new map.

Sent from my SM-G960U using Tapatalk

Tell me about it, seemed such a decent lad aswell. Really should have had a look under when i bought it but you live and learn, and I did knock him £500 for the fact it had failed on emissions. Good things are the car body and interior wise are in excellent nick, with a load of recent receipts for cambelt, dsg service, cam follower, diverter etc. and underneath the car is immaculate also with no rust whatsoever and also looks to have been recently undersealed.

Now to fix this headache, are there any good value full system packages about? If not is there any value in buying second hand, thinking longevity. Do I need a full system or just the downpipe w/cat?  The milltek systems etc that people have do these have sports cat also? Any issues getting them to pass mot? So many questions! If anyone has any suggestions for the best value solution to this (that doesn't involve a loud exhaust!) then I'd love to hear them. Thanks 👍

Offline fakie1977

  • Always Involved
  • ****
  • Thank You
  • -Given: 4
  • -Receive: 7
  • Posts: 120
    • Email
Re: New mk5 owner with lots of questions!
« Reply #24 on: January 08, 2021, 10:56:09 PM »
Was there not someone who replied earlier who would be interested in swapping your exhaust for their standard one? Did you reach out to that person to see if that could work?


Sent from my iPhone using Tapatalk

Offline Jons1001

  • Always Involved
  • ****
  • Thank You
  • -Given: 2
  • -Receive: 0
  • Posts: 54
Re: New mk5 owner with lots of questions!
« Reply #25 on: January 09, 2021, 04:22:49 AM »
Was there not someone who replied earlier who would be interested in swapping your exhaust for their standard one? Did you reach out to that person to see if that could work?


Sent from my iPhone using Tapatalk

Hi, I haven't messaged them yet as still considering my options. One of my concerns is how long should a standard downpipe w/cat last, is it the life of the vehicle? Don't really want to be replacing again soon after. Also I have the original rear backbox but straight pipe in the middle.section, would orignal downpipe ---- straight pipe ---- original backbox be overly loud?

Brian you mention running with sports cat/original cat won't do damage with map but won't run as good, does this just mean less power or could cause other issues running lean/rich etc. because if so I think for peace of mind I'd want to get the map redone. There is quite a few breaking aswell so considering this option (buying original downpipe/centre section) but just depends what condition they are in and how long I can expect the cat to last. Cheers

Offline Jb55

  • Always Involved
  • ****
  • Thank You
  • -Given: 1
  • -Receive: 10
  • Posts: 88
Re: New mk5 owner with lots of questions!
« Reply #26 on: January 09, 2021, 07:37:40 PM »
Just putting this out there but a lot of sports cats will only last a mot or two if your lucky, some won’t even pass the first mot so choose wisely and do your research.

If it was me and funds wasn’t a issue I’d speak to the chaps at powervalve as they seem to have the best sports cats / exhaust systems with 3 different sound profiles , they are active on here as well from time to time.

Offline Jons1001

  • Always Involved
  • ****
  • Thank You
  • -Given: 2
  • -Receive: 0
  • Posts: 54
Re: New mk5 owner with lots of questions!
« Reply #27 on: January 09, 2021, 08:17:48 PM »
Just putting this out there but a lot of sports cats will only last a mot or two if your lucky, some won’t even pass the first mot so choose wisely and do your research.

If it was me and funds wasn’t a issue I’d speak to the chaps at powervalve as they seem to have the best sports cats / exhaust systems with 3 different sound profiles , they are active on here as well from time to time.

Hi mate, appreciate the comment and that is definitely my concern that the cat might not pass. However funds are an issue to an extent that's why I'm thinking of getting the sports car welded in, means i don't have to buy and fit a new downpipe (do have to pay for the weld though) and also should work better with the map as opposed to going back to stock?

Been recommended two high flow sports cats one by magnaflow at £120 and one by darkside developments at £200. Add prob £40 to weld. New downpipe with sports cat start at about £350 plus however much to fit. Also advised to weld in close to the turbo. Any views on if this is the right way to go or recommendations please let me know.

Offline Jons1001

  • Always Involved
  • ****
  • Thank You
  • -Given: 2
  • -Receive: 0
  • Posts: 54
Re: New mk5 owner with lots of questions!
« Reply #28 on: January 10, 2021, 06:17:57 AM »






https://ibb.co/f943xxV
https://ibb.co/tDC8FzZ
https://ibb.co/8xqVBCp

Here are some pics, can anyone tell from these what size the downpipe is? Looks like it reduces at the standard rear section. Also where would be best place to weld a sports cat and will it need to be removed to do this? Thanks

Offline LC5F

  • Always Involved
  • ****
  • Thank You
  • -Given: 9
  • -Receive: 20
  • Posts: 339
Re: New mk5 owner with lots of questions!
« Reply #29 on: January 10, 2021, 02:08:46 PM »
Been recommended two high flow sports cats one by magnaflow at £120 and one by darkside developments at £200. Add prob £40 to weld. New downpipe with sports cat start at about £350 plus however much to fit. Also advised to weld in close to the turbo. Any views on if this is the right way to go or recommendations please let me know.

I personally always find Darkside stuff to be very pricey - wouldn't be surprised if their one is the magnaflow re-badged with darkside premium tax added.

Cats need heat to work, if they are too far away from the engine they will take longer to heat up, so close to the bend is best.

Milltek sport cats are available on ebay from a good seller here: https://www.ebay.co.uk/itm/VW-Golf-VR6-GTi-G60-MILLTEK-Sport-Hi-Flow-Sports-Cat-Weld-In-2-50-63-50mm/162084814001?hash=item25bd01fcb1:g:MHkAAOSwagdXR6-v that's a 2.5" - need to match the size of your decat pipe price is £150 to £170, I would be confident of brand and seller.

If the welder is to do a proper job they will need to take the downpipe off to weld everything up + turbo studs like to snap too - there may well be more expense here.

At some point in the future I plan to upgrade my standard downpipe to a sport cat, my plan is to go for a Pipworx one, they have a good reputation on here and quality looks great https://www.ebay.co.uk/itm/golf-mk5-gti-3-Exhaust-Down-Pipe-High-Flow-Sports-Cat/300361586764?hash=item45eef2184c:g:BVcAAOxybi9RcZgj anything cheaper looks like a real step down in quality.  If you can stretch the money it should be a more predictable result + you can sell your de-cat pipe un-damaged to get some of the money back.