Exhaust Mods and MOTs?
- Thread starter Shady0808
- Start date
Pretty sure that decat has been a problem for mot even before the latest changes... Getting decat has three options:
1 don't do it
2 put decat on for the test then remove it
3 bent mot
Sent from my LG-H930 using Tapatalk
See reason for rejection #3
I've run my RS3 with Milltek secondary cat by-pass from near new and the emissions easily pass: with secondary cats the CO was 0.01%, 0.02% without, and the pass limit 0.20%. However, an MOT tester now needs to 'count' the number of cats fitted and not just take a 'measurement'. So don't use an Audi dealer for MOT, find another and if possible one that can't count.
I've run my RS3 with Milltek secondary cat by-pass from near new and the emissions easily pass: with secondary cats the CO was 0.01%, 0.02% without, and the pass limit 0.20%. However, an MOT tester now needs to 'count' the number of cats fitted and not just take a 'measurement'. So don't use an Audi dealer for MOT, find another and if possible one that can't count.
I would start to think off Sport cat with enough cells to pass the emissions test and you should be fine or keep stock exhaust and you will defo be fine .
But if your a Rebel go the other way and get rid off the cats .
But if your a Rebel go the other way and get rid off the cats .
I had a 200cel cat on my S3 and it was still quite restrictive at Stg3, but up to Stg2+ the cat supplied by BCS seems to flow well enough and not rob you of too much power.
I have a 200 cel APR cat and that doesnt seem to cause any issues even mated to a stock system. A decat and a non res system might flow better ? but its difficult to see where it would improve my dyno chart so it wouldn't be a priority for me as i am running near the limit of my turbo output already. the APR cast downpipe and cat is a mini work of art, ****** expensive but the finish they get on the inside of the pipework without welds is amazing. Quite how they machine the inside of the welded cat tubes is beyond me but they are mirror finish inside.
A decat would allow for easier flow and would result in lower boost pressure to get the same power. While you can get power out with a more restrictive system it does mean that you have to push the air through much harder (higher boost pressure), but with a better overall flowing system you can get same power with less pressure and less heat. With higher pressure, you will see higher EGTs and hotter intake air, which you don't want as that can cause issues with detonation and component wear. Obviously with a better flowing system the turbo would not have to work as hard, thus extending it's life.
I think a well flowing sport cat is fine for anything up to Stg2+, at which point you will start to see the turbo run out of puff, which is where a decat can help things flow better and offer same or more power at lower peak boost pressure. I was happy with a sport cat even with TTE420, but after seeing what can be done without it, consider my mind changed haha
I think we are agreeing Lesh 
I dont think the OP is running a 420 TBH so really my point is why de cat with less than 400bhp unless its about saving money in which case he is in the wrong game tuning an Audi
Right now i have decided that apart from the DSG map which i must do i will be losing weight to improve performance, already a stone down in 6 weeks , another 4 stone to go and that will be 32KG off the on board ballast (me)
I dont think the OP is running a 420 TBH so really my point is why de cat with less than 400bhp unless its about saving money in which case he is in the wrong game tuning an Audi Right now i have decided that apart from the DSG map which i must do i will be losing weight to improve performance, already a stone down in 6 weeks , another 4 stone to go and that will be 32KG off the on board ballast (me)
- Joined
- May 23, 2017
- Messages
- 86
- Reaction score
- 3
- Points
- 8
I've a Miltek sports Cat.
I failed my MOT on emissions so went somewhere where they could turn a blind eye.
Not sure if some sensors on my exhaust aren't a bit dodgy my fuel is running rich
I failed my MOT on emissions so went somewhere where they could turn a blind eye.
Not sure if some sensors on my exhaust aren't a bit dodgy my fuel is running rich
Was the cat properly hot before they did the emissions test? That makes a lot of difference.
- Joined
- May 23, 2017
- Messages
- 86
- Reaction score
- 3
- Points
- 8
Yea first time it wasn't
Second time I went for quite a long run revving a lot low gears kept the car running. Waited a bit before a re-run the results were better but still failing.
The tuners reckon maybe lumbar sensor is faulty.
Second time I went for quite a long run revving a lot low gears kept the car running. Waited a bit before a re-run the results were better but still failing.
The tuners reckon maybe lumbar sensor is faulty.
I usually pop mine along to the garage it does my car and get him to check it will pass before it heads to the Mot .never failed yet but there is always a first so keeping fingers n toes crossed come Feb 2019
Who tuned the car? If they're local, you could try reverting the car back to stock in case they're adding too much fuel low down.
I had a 100 cell sports cat on my S3 and although the MOT tester had to warm it up for at least 10mins, it always passed. I think if your lambda has failed you would get an EML on? I was going to say something about lumbar, but I didn't want to get your back up
