[Spinner]

Having been told for the last 2 years that cat removel meant an engine drop and then seeing it reported that this may not be the case I investigated further with MRC. It appears it is possible and therefore I've now got agreement from Milltek to design a 3" system

Will keep everyone informed of progress.

 

[ecrew16]

Nice, keep us updated!

 

[IbiS5]

Spinner, you're the man, first the supercharger, now cat removal... I already have my Milltek DP and Non Res

 

[Spinner]

Milltek also used my car for the design of the DPs IbiS5, the original intention back then was to remove cats but Milltek struggled to see how they could remove one bolt on one of the cats, got a Master Tech in who told them it wasn't possible without an engine drop. MRC confirmed some others beliefs this is not the case so hopefully we'll get it sorted this time.

And there was me saying no more modding for a while, let alone guinea pigging again LOL

 

[kenny]

I'm saying nothing Matt

 

[Bader.Abbas]

i love my milltek non-res + awe downpipes
but this will make me love it even more

 

[Audilicious]

educate me a little here please, what does this cat removal do to a 4.2?
perfomance, better sound? CEL?

 

[almostS50]

If you remove the cats and someone correct me if I am off, you get louder sound better performance and a nice boost in HP. However you would need someone to tune the car so you can get by state emissions inspections. Everything us A/S 5 owners ever wanted

 

[bhk1004]

With a tune and highflow cat b7 s4 owners saw 30+ whp gains. That would make me a happy camper. Spinner. Is the knowledge of how to remove the cats going to be share with the community? I can't do straight pipes but highflow cats will let me pass emissions and get sexy power... ahhhhhh can't wait... I hate you.. so jealous..

 

[Spinner]

That's correct almost50, it's all in the ability to breath and heat reduction. Milltek got 30-35hp gains by opening up the top end of the exhaust and tuning on the RS4's so it wouldn't be unreasonable to expect similar gains for the S5. Not sure how much it'll give those with a blower, the ristriction I'm aiming to remove is build up of heat, any further breathing gains will be a bonus. It will make it louder. Anyone who's heard my car (Milltek DP's and non-res) will know it's LOUD, 4k rpm test at Castle Coombe recorded 110db which was right on the limit of being aloud on the track and beyond most track limits. I'll almost certainly be reverting to resonated to compensate for the increase but we'll see how things develop.

Here in the UK we require cats to pass our yearly inspection (MOT once the car is 3 years old) so we are aiming to remove the primary cats but install race cats further down the system which should suit your requirement bhk1004!

All info will be shared as it we get it. I'm back at MRC on Wednesday so will see if I can get advice and pics of how they'll instruct Milltek to go about it.

I'm not expecting this to happen to quickly, from what I'm lead to believe Milltek have been doing up their workshop so well behind on development. Realistically I'm going to have to pull a few strings to get things moving on a reasonable timescale.

 

[Spinner]

I'm not planning to replace headers at the moment Najibkassis. With cats removed the headers will end up being the restriction as they appear to be double skinned so smaller than they look from the outside but by comparison to the cats the belief is this restriction will be minimal.

My car is at MRC today, they've had to drop the subframe to get to the bolt that was previously inaccessible. Everythings off but due to the difficulty of removal I'm not sure if this is going to be a viable option as a production run for Milltek. I'll be speaking to MRC and Milltek tomorrow about how we progress and will report back.

 

[crisp74]

thanks for the update spinner. very curious as to how this turns out. even if it does not go into mass production, let us know what kind of gains you see on your car.

 

[Spinner]

Will do, having just spoken to MRC they're going to see if they just gut the cat or cut and just weld a straight pipe in it's place, then they'll obviously have to tweak the map accordingly. If this works then we'll be talking to Milltek, apparently in MRC's experience is that they may still do it as there is a similar problem on the B5 RS4's where they need to drop the rear subframe yet it still went into production.

 

[Spinner]

Got the car back on Thurday evening.

Bottom line there's not enough room for 3" downpipes (specifically the right hand side where the pipe actually has a kink in it just so the could fit the stock 2.5") so de-catting is as far as this mini project goes.

Are there gains? Yes, we believe so. I don't have solid comparison facts as MRC didn't dyno the car before removing the cats. On the Dyno afterwards it made 522ps and 618nm torque which is slightly under what the car originally produced when the blower was first installed. However we are now running approx 20c higher ambient temps so there is clearly some gains. How much is related to purely the cats it's difficult to say as the newly installed water/meth is also working well. The biggest gain on my car is going to be removing the heat restriction as being FI'd the air flow restriction will be far less than on a NA. I'd fully recommend de-catting for anyone running FI on the V8.
Would I recommend this on a NA car? That's a difficult one, had 3" downpipes been viable then based on what the B5/6/7 community state then it would have been a defiante yes. Ultimately until someone tries it with a tune to match you'll never know!

How does it sound? Frigging mental! It's a 10db increase, a little raspier (perhaps very slightly tinny) but still with the deep burble in the background. There is however a downside, the drone at 2k rpm is almost unbearable and I'll now be forced to try out to my resonated middle box to see if we can improve this. Will get some video's done in the near future but as we all know, recordings never do an exhaust note justice!

 

[bhk1004]

So in the end they couldn't remove the cats? They just cut and rewelded?

 

[Spinner]

They were able to remove the cats by dropping the subframe a little. It's one bolt on the right hand side thats otherwise inaccessible. As there is no room for a 3" pipe it was a straight pipe replacement once they were removed.

 

[bhk1004]

Well for NA 3 inches probably would actually cause too much loss in back pressure. Probably better that they can't fit it. Anyways they gonna make the pipes for everyone?

 

[Spinner]

As MRC fab'd the pipes for me I'm yet to speak further to Milltek. Tbh considering the need to drop subframe and not being able to go to 3" they may well decide it's not worth it.

Re the 3" exhaust, according to the 4.2 Multiport guys they benefited from going to 3" systems, I know they're not FSI engines but one would assume this would have been a worthy upgrade had it been possible.