I just had my Octavia decatted today. Thought i'd give a review for other people considering it.

Cost me £50 all in, so I can't really complain even if the results were very little change. But after doing about 50 miles in it, I can say that there is a difference to be felt.

The car revs quicker and the turbo spools up alot faster. Can't say too much on fuel consumption as of yet, but I think that driven normally it will return a better mpg than before, even if only by 1 or 2. I put this down to the smoother and more effortless acceleration. The biggest difference I have felt, is accelerating from low RPM in a high gear. Say sitting at 30mph in 5th, where as before, by planting your foot, it would take a good few seconds to pick up to any noticeable increase in speed, it now feels to be a faster sequence. Putting your foot down makes an almost instant reaction as if the revs were higher. At low revs (1200-1500 rpm) this is not something I could have said happened before.

The cat weighed an absolute TON when taking it off. By turning it on it's end, there were mountains of soot and carbon coming out of it. This I imagine was heavily impeding the flow of gasses.

There is also a slight increase in the whistle from the turbo. But this is only noticable if you stand outside the car. Or have window down. I was considering having the silencers removed aswell, but I'm not one to draw attention to the car and make it sound something that it isn't. Hence I rate the decat as a good mod since theres barely any noticeable difference to anyone but the driver.

Out of interest, does anyone know what the silencers are filled with? Do they impede the air flow much?

Hi,

I was thinking about having this done,\where did you get yours done?

Was looking to get a bigger downpipe though...

I got it done here...

http://www.ioxfordshire.co.uk/profile/228011/Bicester/Weston-Garage/

They were friendly and did the job quickly. I did have to wait for a while but that's because I just turned up instead of booking! I would reccomend.

Cheers mate

Doesn't removing the CAT have a possible implication on the MOT? That would be my main concern . . . .

As the MOT for diesel engines only employs a smoke test, NOT an emissions test, removing the CAT has no effect on the MOT at all. I feel that if anything, removing the CAT may have cleaned up my exhaust smoke due to the amount of powdery carbon deposit which was sat in the CAT upon removal. With a few vibrations from rough roads and then hard throttle, I imgaine some of this deposit is blasted from the exhaust.

I will update you when my MOT is next due in may. But have been assured by many other sources that it won't be a problem and have not heard of any decatted diesel not passing it's MOT for those reasons.

As a further side note, you can be failed for exhaust volume being deemed too high by the tester. Having my car decatted seems to make little to the exhaust note however. This is purely subjective anway.

I have heard reports of cars post 2001 having to have a CAT for testing, much like petrol engines post 1993. But i'm yet to see anyone quote this law from a reliable source. This one seems to be hearsay. Many people on the Seat forum, having the same engines as us, have had them decatted AND the silencers reomved and sailed through all the MOTs since.

The reports which have been backed up by sources are the ones which state you can fail if part of the exhaust system is missing or leaking. However it does not state that having no CAT is a fail.

If the tester pics up on this rule, I would be inclined to use the "it's a repair job as the CAT got caught on some rough terrain/rock in the road/uneven curbstone and pierced when I was driving causing it to leak." As in that scenario, you would be failed for having a leaking system.

As said, I can't garuntee anything having not gone through a MOT myself yet. I feel confident though. I will post an update in May when it's due if I remember!!

my old tdi has just sailed through its MOT without a CAT fitted

Matt, out of interest what year was the car in question?

2004 pd130, mapped with approx 137,000miles

Edited 14 March, 201016 yr by matt@theforce

Thanks for this matt. Yet another example dispelling this post 2001 myth.

http://www.motuk.co.uk/manual_710.htm and http://www.motuk.co.uk/manual_740.htm seem to apply. There's no mention of a catalytic convertor in either of them.

Note: A durable repair to an exhaust system which effectively prevents leaks is acceptable

Thanks for the links. This above quote could well prove to be the most useful. In the sense that as long as the job is done to a decent standard, claiming it's a repair should get you through any situation. Although I maintain it's unlikely there will be any issue anyway!

not a problem at all on diesels all they are tested for is visable smoke when revved abd that applies to all of them from 1990>2007 (as need to be 3 yrs old)

some of the later engines employ an emmision sensor in the downpipe and may get the pig a bit with no cat but they are mainly the cars with DPF's.

i decatted my 110tdi octy and fitted a small straight thru rear silencer and found the throttle response was vastly inproved but it did drone a bit from the exhaust so i went back to the std rearbox with sone internal mods..

we cut one open all the way round and the exhaust gas has to go all the way to the back then into a chamber and thru a smaller dia pipe to the front of the box then thru some baffle plates into the middle and 2 pipes out. it was absolutly full with soot (caught fire from the grinder lol) and i welded it back together with some large holes cut into the baffle plates and stuff to make it free'r flowing.

Is anyone running just a straight through pipe?

Is anyone running just a straight through pipe?

Try PM-ing TrevorB33 I think he had a straight through pipe on his TDI at one point. It makes it sound like a tractor though :no:

Edited 17 March, 201016 yr by chicken_eyebrow

Thanks Mate.

I've seen many videos of vag diesels with straight through exhausts (youtube 110 tdi straight through or decat etc) sounded a bit too hardcore for my liking! But removing just the cat makes very little audiable difference whilst still improving flow. I don't think the silencers impede the flow of gases that much to be honest. If you wanted to go the whole way, then you could open up one of the silencers and remove or cut apart some of the baffles having a similar effect to a straight through, but hopefully still keeping noise down.

Hi I've a very similar car L&K 130bhp estate as the systems just broke where it goes onto the CAT think it's a good time to do this mod.Have spoken to the garage did you have it emissions tested afterwards? As they told me about somebody thought it may be you?What about sensors does this cause any running issues.

Hi I've a very similar car L&K 130bhp estate as the systems just broke where it goes onto the CAT think it's a good time to do this mod.Have spoken to the garage did you have it emissions tested afterwards? As they told me about somebody thought it may be you?What about sensors does this cause any running issues.

I had no issues at all when my pd130 was decatted, no warning lights and no issues come mot time.

Get it done, it's well worth it.

Matthew

HI

Yes we do the Milltek downpipe without the cat

We used this on Matts Octy , and that was OK

Was a good little write up somewhere wasn`t there Matt?

Sarah

I can only agree, get it done. It's well worth it.

HI

Yes we do the Milltek downpipe without the cat

We used this on Matts Octy , and that was OK

Was a good little write up somewhere wasn`t there Matt?

Sarah

Sarah,

There is indeed a little write up Miltek Write Up

Worth noting that my write up covers the whole resonated Miltek system and not just the decat.

Matthew