Catalyst replacement

tintin · #1 14th October 2014, 01:47 PM

I've been told by both Audi Stockport and my local Kwikfit that my cats need replaced - one's collapsed, and one may be about to, so I'm starting to look at options - I've read the thread started by Reffro, which has some useful info, including some specialist suppliers (such as the one use by Jim/Brian in Kirkintilloch).

The cost of OEM replacements is eye watering at c.£1500 each, so I may make an exception to "all OEM" on this occasion, and - as usual - all ideas/suggestions very welcome.

I've got some fairly basic questions to start with tho'

1 - how long can I drive with the car in it's current condition? (it was one of the reasons I didn't make it to last weekend's meet)
2 - what do they do with the old cats? presumably they're worth something, being precious metal n'all…
3 - sports cats seem cheaper and better - why would I not go for those?
4 -should I replace one or both?

Goran · #2 14th October 2014, 02:55 PM

Check out HJS cats, made in Germany and apparently very good quality. I just bought two 200 cell cats for around £640 delivered. I put a pair of HJS cats on my previous S8 too, I had no problems for 4 years before I sold it.
The only catch with 200 cell cats is they may trigger the CEL from the post-cat lambdas. A simple solution is either spark plug anti-foulers to move the lamba out of the exhaust flow, or to get the post-cat lambda error coded out. The lambda has to stay in there as it is still used in the fuel maps (as far as I understand it) but it wont produce error codes or trigger CEL.
On my previous S8 I had a pair of these Wayne Angles to stop the CEL, and I only had a intermittent post-cat lambda error code but never a CEL.
http://forums.vwvortex.com/showthrea...ear-02-Cel-Fix)

http://www.hjs-tuning.de/de/3/71/0/s...universal.html

I bought a couple of these HJS-Nr. 90 95 0092
I got them from here, good service arrived in less than 1 week.
https://www.turboperformance-shop.de...s-bis-2600-ccm

They should be fine for our engine size and HP looking at the HJS data. Or you can get bigger ones if you want.
Also I'm not sure if you may need a remap because of freeing up exhaust flow? If your current map is to get the best performance with current cats, you may lose some performance with free flow cats unless mapped for them? I cant really advise on this we need a engine/exhaust guru to answer that one.

More info from AWE who also sell HJS cats. Cheaply made aftermarket cats can telescope because they are wound just like toilet paper. Properly wound cats are wound in several ying-yang spirals (for want of a better description

) for a much stronger structure.

http://forums.vwvortex.com/showthrea...t-vs-metal-cat

one more bit of info, MRC charged £150+VAT to code-out post cat lambda errors. However, if you are going for a completely custom map maybe you wont need the post-cat lambdas at all?

ainarssems · #3 14th October 2014, 03:02 PM

1. Depends on your luck, could drive forever or at least till next MOT, or a big chuck could turn sideways and block exhaust any moment.

2.Here is the guideline prices for diferenf scrap cats,as you can see prices vary a lot from nothing to over £200 http://scrapmetalforum.co.uk/phpbb3/...php?f=15&t=475

3.If they are TYPE approved I don't know why unless you are 'treehugger' and want to do every last bit to save the environment, but seeing you drive S8 yuo probably don't care about that much. If not TYPE approved they will be MOT failure unless you have a friendly MOT tester.

4.If you replace them like for like with second hand unit for example you can do only one. If going for aftermarket then better do both at the same time.

Goran · #4 14th October 2014, 03:54 PM

I forgot to add, I ran my old S8 with no remap for the HSJ cats and just the L-shaped anti foulers.

tintin · #5 15th October 2014, 01:44 PM

Cheers Guys - As a first step, I'm going to pick the brains of the guys who replaced my Coupe exhaust, MIJ in Birmingham. Lots of research and input before acting, I think...

Adrian E · #6 15th October 2014, 02:09 PM

To answer the question about the cell count - the lower the cell count, the less restrictive the exhaust, but also the less effective they are at doing their job.

Properly warmed up a low cell count cat should pass an MOT.

If you wish to retain originality and aren't looking for additional performance then cats with similar properties (ie more of the expensive material in them!) will work just as well as the factory cats, but may not last as long.

A replacement cat for a post 1/3/2001 vehicle should be Type Approved and carry an e-mark to show it complies with Reg 103 - worth checking although as above you may get away with it if they're not and it passes the emissions test anyway.

slowwy1 · #7 15th October 2014, 03:14 PM

I had to replace one of mine a few years ago. I can't remember the extact price but I think it was ~800+VAT from TPS. Emissions practically went to 0 after that. There was nothing left from the damaged core so emissions were on the limit with one good catalyst.

Old cores are normally crushed and sent to the US for precious metal extraction. I don't think anyone has the facilities to do this in Europe.

"Sports" cats are normally metallic cores instead of ceramic and usually have 0.5-1g of precious metals compared to 5-6g for the good OEM ones. VW ones are quite good and worth a reasonable amount for scrap.

HJS are certainly the ones to go for if you decide against the OEM ones.

Goran · #8 15th October 2014, 06:11 PM

I hesitated posting this, but best to be informed, check your MIJ exhaust with a magnet, if it sticks I doubt it is 'proper' T304 steel.
I need a whole new exhaust soon and based on my research I would go to Primary Designs as a first choice. Pricey I know, but it is for a S8.
http://www.primarydesigns.co.uk/
I have visited them before, they are very friendly. People who can make Inconel and titanium exhausts must be quite skillful.
As a second choice and on a budget I would go to Infinity-Exhaust in Bristol. Lots of good reviews on the web and on pistonheads for what its worth.
http://www.infinity-exhausts.co.uk/

I am just a web digger, best to trust your own research

briang9 · #9 15th October 2014, 11:02 PM

only problem I have with my "sports cats" is they trigger the EML, they are efficient enough to pass an MOT but don't meet Audi original spec parameters, I have had a quote to code out the check but that was around £350, an £8.99 ebay code reader that can cancel the codes and reset the light was a more cost effective solution. For what it's worth I think the car sounds slightly "throatier" with the sports cats. Mine were £500 for two with lifetime warranty a few years back.

Goran · #10 16th October 2014, 08:54 AM

Try the anti foulers to move the lambda out of the exhaust flow, I never had a light CEL for 4 years with that set up, only the occasional error code but the MOT guys never noticed that.
And those cats were supposedly 100cell (that's what I asked for anyway) they were HJS too.
Or ask MRC, they coded mine out for £180, and that price includes coding out the pesky SAI pump.