Downpipes

[Northerner]

Having had a chat with MRC about power options, it appears that the bulk of the power uplift from an exhaust change comes from the downpipes & sports cats replacing the OE items. As i'm not after more exhaust noise, i'm thinking of just having the downpipes and cats placed and leaving the OE sports exhaust in place.

Has anyone done this and did it make much difference to the noise levels & power? Also, which are the best downpipes and sports cats to go for?

[MikeFish]

What are you trying to achieve? More power? Then just get a remap.

Sports cats are a waste of money in my opinion. They are quite expensive for relatively small gains. Either decat with remap for ultimate power gains (approx 740ps) or just remap for almost the same gains (700ps +).
You didn't say if you wanted a remap? Sports cat with no map will add very little indeed and probably still invalidate any engine / gearbox warranty.
I don't know anyone who had fitted sports cats (probably for the reasons I just explained). But I have heard a decat with standard exhaust and it sounds amazing but much louder than standard.

[MikeFish]

And if you go decat you will need a remap and a friendly garage to do your MOT.

[gsc]

I'm probably going to look at modified freer flowing downpipes with integrated race cats coupled to OEM cat back sport exhaust as I'm after better sound than a cat back can produce but not bothered about ECU remapping or significant power gains or the headache of them not passing MOT if not through a 'friendly' station. Heard plenty of exhaust options last weekend at Combe and whilst they sound nice, none are as base in tone as a n/a V8. Freer flowing downpipes and cats I believe could be the solution to this

There is potential a local exhaust Shop to me will custiom fabricate down pipes with GESI cats i the same place as the OEM cats for £1200-1500, so less than an off the shelf cat back and if they have the template may fabricate others, still in discussion. Will update if it becomes more of a reality. Slightly more if they ceramic coat them.

[dasquade]

Recently gone ceramic coated catless downpipes combined with non-res milltek on my S6. Was already stage 1, now stage 2. Even stock or tuned, you don't want catless or sportcats for additional power (i only gained around 30hp/40nm) BUT it did open up the flow and with optimized tune you get a better turbo spool.
Note: if you don't do a remap, you might even create more turbo lag as you took out the backpressure resistance of stock cats.
Only true benefit is better flowing exhaust and less trapped heat inside.
Downside, with valves open....it is very very loud and in millteks case, rather a raspy sound (mainly due to the fact you can hear the wastegate flaps rattle for example).
With valves closed, it actually sound very nice and deep .
Sport cats might give you more or less your desired V8 sound, but beside that it won't give you much bang for your bucks.

[Northerner]

It will be remapped as well. Thinking on, is there anyone in the South Yorkshire area with a milltek fitted to their c7 who wouldnt mind me popping over to hear how loud these exhausts actually are?

[Tadass910]

Best in my opinion to make remap, stage 1 leaving stock downpipes and adding nice Miltek none resonated version, in flesh sounds deep and nice v8:)