IanH's C6 RS6 - 925hp & 1150nm - Updated 06 Jun '25

[Ian_C]

Dodged a bullet there with the tyres and the missing wheel bolt!

[IanH755]

Yeap, mostly just a consequence of my own lack of attention down to just not driving the car anywhere near as much as I should be.

[IanH755]

So after a quiet 6 months, what's new? Well pull up a chair and let me tell you the tale of how a simple exhaust change reminded me that - my maths maybe not be same as everyone else's maths, which caused a bit of an issue!

First some history on my exhaust - originally this was a complete Frankenstein's monster, with an MRC Tuning set of 3.5in to 3in de-catted downpipes leading to a custom 3in removable cat/de-cat section, then a KWE 3in cat-back bought from Germany which turned out was jigged incorrectly and needed a load of custom work to fix, no resonators and no X or H pipe linking the two exhaust pipes (so effectively each 3in exhaust pipe was only linked to half an engine i.e. a 475hp 2.5L I5).

What were the issues - well, to start, having to swap the cat back/forth at MOT was always a bit of a pain to do (arrive at garage, let exhaust cool, remove de-cat and fit cat, go for a blast to heat up cat to pass MOT, go to MOT place, come back to garage after MOT, let exhaust cool again, remove cat and fit de-cat, go home), and whilst I absolutely loved the "raw, aggressive and loud" noise and tone made by this hodgepodge of an exhaust, to everyone else it was "raw, aggressive and loud" as well, to the point that not only were the neighbours quietly twitching curtains and raising pitch forks every-time I went for a drive, but it was so loud that even my mates 10yo kid didn't want to go in the car anymore because it hurt his ears etc etc.

So, knowing that I won't be keeping this forever, and who ever owns this next likely won't be happy with a family car that could deafen the dead, and in an effort to solve my Cat/De-Cat pains, I decided to get a whole new custom exhaust to join onto the existing downpipes. First off I knew I wanted to permanently fit a set of cats, just to make MOT time so much easier, so I looked around for a set of Cats which would "easily" pass an MOT - This was a big mistake and caused every other problem I'll tell you about later - My old cats were about 10 years old, made by ARLOW in Germany and were a 100cell Euro 4 metallic cell Cat which sometimes still struggled to pass emissions and were getting worse with every MOT so I didn't want to reuse these.

After a search I decided to go "overkill" and get a set of 400 cell, Euro 6 metallic Cats - so more cells and a "better" chemical dope applied to remove even more bad stuff from the exhaust gas (wow, so technical ). Now I knew more cells = more restriction so I looked up "how restrictive is a 400 cell cat" on the mighty Google, and the general consensus from a few places was that, for a metallic structure like mine, it was about a 10% restriction so I thought "if I buy a 4in wide cat, then if I knock off 10% = 0.4in which means the 4in wide Cat will flow the same volume of gas as a 3.6in exhaust - so no restriction at all, winner!!!!" and bought a pair of these from Alpha Performance Fabrication.

Next I needed a custom fabricator, and having had a look around my "local-ish" area of Norfolk I'd seen that Demand Engineering near Diss had done a quite a few custom exhaust for other C6 RS6 with similar power levels, only I found out they no longer do custom work and only do Land Rovers, so I looked around again and eventually found Edwards Motorsport near Kings Lynn who do all kind of custom metal work (cages, exhausts, manifolds etc, any custom metal work really), and I knew the name seemed familiar but couldn't quite place it, until during a web search it turned out they'd been involved in fitting an RB26DETT engine from a Skyline GTR into a Lotus which had its own thread on the GTR Owners club, and I was still a member of the club so remember reading about it (small world).

Anyway, after a visit to confirm what they could do based on what I wanted which was to stay with 3in pipes and then go from the existing downpipes into my supplied cats then X-Pipe - resonators - quieter back boxes - finally re-using my existing oval tips - we shook hands and I left the car with them for a month whilst I pootled around in the Citroen C1.

Now, I knew that I'd have to get the car map checked out after having this work done as, even though "I'd done all my calcs and I knew it was OK" I juuuust wanted to be sure that the cats and the exhaust weren't somehow a restriction or were maybe just a tiny one at worse (ah hubris in action!). After picking up the car the difference was amazing, just what I wanted with the volume levels (almost OEM) I wanted, so now you could actually talk to a passenger rather than shout at each other and my stereo didn't have to be turned upto 11 to drown out the droning past 40mph.

Happy with my choice in fabricator (great welding work BTW!) I drove down to MRC Tuning a few days later and let Doug loose only to have him return after a few pulls looking very unhappy for me - the issue was that my "amazingly well calculated Cats restriction frontal area maths" actually turned out to be utter rubbish, and the cats were such a massive restriction that, to the car, it seemed like the OEM 2.5in exhaust had been refitted, with the car (previously 955hp & 850lbs/ft) had now dropped to 750hp & 666lbs/ft with some impressive lag and it was obviously not being happy about being unable to breath out properly, with Doug being concerned that, with the RS6 not having any EGT's from the factory, he couldn't be sure just how hot the exhaust was getting so he wasn't confident that it was safe at full throttle, even if down tuned.

Ah balls!

So, with Doug giving me a sort of "emergency" map of wastegate only boost and a promise not to go full throttle until the problem was fixed, I trudged back home to figure out what to do next, other than the already made decision to cut out these restrictive (for my car) Cats. I decided to ring Edward Motorsport in a flapping panic and they were able to grab some spare time to chop out the Cats for me and stick in a "temporary" swappable cat/de-cat section, which immediately solved my "OMG the engines gonna melt" issue and would give me time to come up with a better plan.

I also had to travel back down to MRC Tuning for Doug to undo his previous map and find out how restrictive the new exhaust was, being much, much quieter than the one which made 955hp - this time Doug was full of smiles for me, 925hp & 850lbs/ft with no issues, so a small 30hp drop to solve a massive volume/noise problem, I was very happy with that!

Well, now I've got a decision to make -

* A - Stay with the swappable cats and just re-use the "restrictive" Cats for MOT only as the car won't be doing over 3000rpm with them fitted - zero cost option but back to the same old "in/out" issue with the cats.

* B - Find a set of non-restrictive cats to have permanently fitted and another remap for them. This solves the Cat in/out issue but chucks in a big one in its place. I spoke to HJS who make Cats for high power cars like mine (which I should have done in the 1st place) and they recommended the biggest Cat they do - a 6in 200 cell Euro 6 one - which they guarantee will not restrict a 3in exhaust at 450hp (so 900hp for my twin exhaust). So whats the issue - the cost, they're £1000 each

So after many, many thousands of pounds, 500+ miles back and forth to MRC etc I'm effectively back in the same situation I was at the start of all this................but my cars quieter soooooooo

Also, and just to repeat this, Edwards Motorsport really has done some fantastic work for me, all of this faff was created solely by me and my smooth brain!

Here's some pics anyway -





750hp -



back to 925hp -

[don0301]

Just find a garage that will give a ticket pass. Easy

[IanH755]

Just find a garage that will give a ticket pass. Easy

If only it was that easy! I spoke to both MRC and Unit20 who can't find a local "friendly MOT" place anymore, and there's absolutely no-one close to me in Norfolk who are "emissions friendly" either, and all this (according to a few places that told me) is apparently down to a massive crackdown by DVSA and large numbers of "caught being too friendly" testers losing their certification.

I mean, if I could just pop around to my local place for a simple emissions sign-off, I'd be there in a heartbeat - and I'm sure there's still some friendly MOT places about, but finding one has become a pain where I live.

[don0301]

Just find a garage that will give a ticket pass. Easy

If only it was that easy! I spoke to both MRC and Unit20 who can't find a local "friendly MOT" place anymore, and there's absolutely no-one close to me in Norfolk who are "emissions friendly" either, and all this (according to a few places that told me) is apparently down to a massive crackdown by DVSA and large numbers of "caught being too friendly" testers losing their certification.

I mean, if I could just pop around to my local place for a simple emissions sign-off, I'd be there in a heartbeat - and I'm sure there's still some friendly MOT places about, but finding one has become a pain where I live.

I never had a problem in Essex, When I moved to N. Somerset 3yrs ago I had similar experience at first but it's just because they "don't know you" I found somewhere easily enough. Word of mouth is probably your best bet.

You won't get any answer from anyone like MRC or Unit 20, that should be obvious.

[IanH755]

For the first time in what seems like forever, I took my car out to display it at a car show, so today I was at Cambridgeshire's largest car show, the 4KAutoShow held at Newmarket Race Course.

There was around 500+ cars on display (my pics just show 1 of the 3 display areas), from various clubs around the area with everything from a Porsche 918 to a rusty VW Polo and everything in-between. With such a varied line up there was literally "something for everyone" and when combined with the awesome sunny weather we're having the day was absolutely fantastic!

I used over 1/2 a tank of fuel in under 100 miles travelling there & back with lots, and lots, and lots of full throttle used on the drive, and despite being a little unsure of how much I'd like the quieter exhaust after nearly a decade of ear-bleedingly loud noise, this trip really showed me how fantastic it is.

Anyway, some pics -









and something thats rare in the UK, when the sun finally comes out the green & purple flake in the paint comes out, taking away some of that "grey box" look to the car to the naked eye (not great at coming across in pictures sadly).

[Ian_C]

Looking lovely.