Downpipes for an Akrapovic Evolution Titanium Exhaust System

[DXB_RS6]

Hi,

I have an Akrapovic Evolution Titanium Exhaust System on the way and I'm looking to add on downpipes then put a stage 2 tune on it.

Can anyone advise where to find good downpipes?

Also, on a downpipe, what is the difference between 90mm and 76mm (Don't say 14mm ) what does the size difference do?

Cheers.

[MikeFish]

The bigger the downpipe the more noise and potentially more power you will get.

Assuming you are going for a non MOT legal option of cat bypass rather than the legal sports cats then there are plenty of options. I don't know if they are all a straight fit onto the Akra though.
Options include milltek, brondex, APR and Akra will sell you one made by the same company that makes their exhausts (or is made by akra but branded by this other company can't remember which way round it is).

[DXB_RS6]

I'd prefer not to touch the cats and also keep the noise to a minimum. I'm willing to sacrifice a few extra HP for this.

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[MikeFish]

So you don't want downpipes then?

[DXB_RS6]

Yes I do, but based on all the advice I've been given, apparently it doesn't increase the sound all that much, especially given the still valve controlled?

Good to hear your feedback, Mike?

Cheers.

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[MikeFish]

What is your aim? More power but no more noise?
Sounds like you want sports cats. But they won't gain that much and set against the costs I personally wouldn't bother. Unless you are looking for maximum possible power then leave the cats alone.
You do realise the cats are in the downpipes?

[MikeFish]

Ie replacing downpipes means you remove the cats.

[DXB_RS6]

My main objectives are: increased power with minimal but nice noise. The demos I've seen of a standard Akrapovic with downpipes and a tune is great for me.

Tbh, Mike, I'm not really very knowledgeable on the mechanics of a car which is why I come on here to seek advice. When enquiring with companies for the downpipes, I was asked the question.. What do I plan to do with the cats?

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[MikeFish]

The downpipes are home to the cats. So people normally replace these with straight through pipes for maximum power. This makes it illegal in the UK and will need to be swapped out for an MOT unless you know any dodgy garages willing to turn a blind eye.
Sports cats would keep it legal but cost a lot more and the gains are much less.
Not sure what the laws are regarding cats in Dubai though.
Personally I wouldn't bother. I think you'd struggle with any engine warranty claims with aftermarket downpipes too.

[Leo-RS]

As Mike has said, if you want to add aftermarket downpipes to your Akra setup you will lose your cats. Another option is to opt for a downpipes with sports cats.

Cats are restrictive and they sap power so if you choose the sports cats option then you will still gain some power from the downpipes due to the cats being less restrictive than OEM cats but obviously it won't be anywhere near as much as to what decatted downpipes offer.

No cats = MOT failure. If you plan on keeping your car beyond 3yrs you either need to find a dodgy MOT station that will pass your emissions for a bribe or you will need to pay for about 12hrs Labour (once every year) to remove your downpipes and then fit the standard downpipes for the test and then swap them back over again for your next 12 months. The job is an absolute pig to do, 6hrs Labour for downpipes replacement.

Sports cats option = Possible MOT pass. Results unknown, its with the gods.

I had the Milltek Turbo back system (Downpipes + catback) on my RS6 but it was new and I had 3yrs before having to worry about MOT time. I don't keep my cars longer than 3yrs so the MOT issue was a non starter for me.

Now, here's the issue you have. You're very expensive Akra exhaust system. It's next to useless if you're after power.

It doesn't matter a cahoot whether you opt for the 2 x 76m downpipes or the 2 x 90mm downpipes as they will be mating upto the Akra system which is of the same size as the standard system (2 x 63.5).

This is the reason why the Akra system fits directly to your stock downpipes. You would have nice free flowing downpipes of 2.75" (76mm) or 3" (90mm) coming all the way down the engine bulkhead only to be met by an Akra 2.5" catback section. So if you opted for the 3", you would get gains of course as you're removing the cats but you would instantly be restricting them by forcing it to force exhaust gasses now through a 2.5" pipe.

That brings me onto my next point, fitment. As Akrapovic designed their system as a cat back only, it was designed to fit to the standard 2.5" downpipes. You see where I'm going? If you want to fit bigger downpipes to your Akra setup, they won't fit. You will need an exhaust Shop to make adapters, you can't fit a 2.5" pipe to a 3" pipe without some sort of adapter/special flange being made.

The Milltek downpipes for example are 2.75" and have to be mated to a 2.75" catback system which the rest of their catback exhaust system is, so that's not an issue. It forces the need to buy the whole system rather than just the downpipes. If you opt for just a Milltek cat back section (2.75") to mate up with the standard downpipes (2.5") Milltek provide a connector pipe that narrows down to 2.5" so it mates. If you then decide to add downpipes, Milltek need to provide you with a new larger 2.75" connection pipe to fit to the larger downpipes.

Then brings me onto the 3" downpipes. It's my opinion that they are overkill unless the rest of the exhaust system is 3" as you then have the same issue I noted before. It would be a 3" going down to a 2.75" fairly quickly. To be honest, I'm not sure the tuners see much if at all any gains in the 3" as opposed to the 2.75". Perhaps more beneficial for big power cars (750hp+) but for upto 750, the 2.75" is fine.

For you going forward, if you really want to press ahead with this, go for the 2.75" Milltek decatted downpipes and ask your exhaust Shop to make them fit to your Akrapovic. They will make a new flange or some sort of sleeve that will mate the two up. You'll still gain a whack of power but just not as much as a full Milltek exhaust would for the reasons mentioned above.

[Leo-RS]

If you're in Dubai you can probably ignore the part about a yearly MOT test unless they do something similar there?

[DXB_RS6]

Thanks for the detailed reply, I appreciate it.

I am aware that by adding only the exhaust system I won't see any power gains really. I bought the Akrapovic for the sound more than anything.

Then I thought of the extra power.

I found 2 options.

Akrapovic + MRC tune stage 1
Or
Akrapovic + Downpipes + MRC tune stage 2.

I was under the impression that going for the second option would take the car to close over 700hp and not increase the sound of the car too much.

As I've mentioned before, I'm not super clued up on the mechanics so I didn't realise that I would have to also change the cat. Nor has anyone mentioned it to me during my purchase enquiring until today.

I was happy with the stage 2 option because I'd get a lot more power but I was told the noise wouldn't increase considerably.

Now we are talking about cats (I thought they we're totally separate to the downpipes and a change was an option but not essential for stage 2) its getting a little complicated and sounds loud to me.



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[Leo-RS]

Loudness certainly increases but only on WOT (wide open throttle) - You are still protected by the valved system in the Akra for normal driving. I'm not sure how much it would change the lovely sound from the Akrapovic though.

It's a difficult one, especially in a hot country such as Dubai. The free flowing downpipes would do you a world of good and give a good noticeable increase in power.

I would think in Dubai with its climate, going for option 2 with the decatted downpipes you probably would get just over 700hp (700-710 I would say). In the UK with its cooler climate this can go upto 740, even 750hp with the downpipes.

[Tadass910]

As Mike has said, if you want to add aftermarket downpipes to your Akra setup you will lose your cats. Another option is to opt for a downpipes with sports cats.

Cats are restrictive and they sap power so if you choose the sports cats option then you will still gain some power from the downpipes due to the cats being less restrictive than OEM cats but obviously it won't be anywhere near as much as to what decatted downpipes offer.

No cats = MOT failure. If you plan on keeping your car beyond 3yrs you either need to find a dodgy MOT station that will pass your emissions for a bribe or you will need to pay for about 12hrs Labour (once every year) to remove your downpipes and then fit the standard downpipes for the test and then swap them back over again for your next 12 months. The job is an absolute pig to do, 6hrs Labour for downpipes replacement.

Sports cats option = Possible MOT pass. Results unknown, its with the gods.

I had the Milltek Turbo back system (Downpipes + catback) on my RS6 but it was new and I had 3yrs before having to worry about MOT time. I don't keep my cars longer than 3yrs so the MOT issue was a non starter for me.

Now, here's the issue you have. You're very expensive Akra exhaust system. It's next to useless if you're after power.

It doesn't matter a cahoot whether you opt for the 2 x 76m downpipes or the 2 x 90mm downpipes as they will be mating upto the Akra system which is of the same size as the standard system (2 x 63.5).

This is the reason why the Akra system fits directly to your stock downpipes. You would have nice free flowing downpipes of 2.75" (76mm) or 3" (90mm) coming all the way down the engine bulkhead only to be met by an Akra 2.5" catback section. So if you opted for the 3", you would get gains of course as you're removing the cats but you would instantly be restricting them by forcing it to force exhaust gasses now through a 2.5" pipe.

That brings me onto my next point, fitment. As Akrapovic designed their system as a cat back only, it was designed to fit to the standard 2.5" downpipes. You see where I'm going? If you want to fit bigger downpipes to your Akra setup, they won't fit. You will need an exhaust Shop to make adapters, you can't fit a 2.5" pipe to a 3" pipe without some sort of adapter/special flange being made.

The Milltek downpipes for example are 2.75" and have to be mated to a 2.75" catback system which the rest of their catback exhaust system is, so that's not an issue. It forces the need to buy the whole system rather than just the downpipes. If you opt for just a Milltek cat back section (2.75") to mate up with the standard downpipes (2.5") Milltek provide a connector pipe that narrows down to 2.5" so it mates. If you then decide to add downpipes, Milltek need to provide you with a new larger 2.75" connection pipe to fit to the larger downpipes.

Then brings me onto the 3" downpipes. It's my opinion that they are overkill unless the rest of the exhaust system is 3" as you then have the same issue I noted before. It would be a 3" going down to a 2.75" fairly quickly. To be honest, I'm not sure the tuners see much if at all any gains in the 3" as opposed to the 2.75". Perhaps more beneficial for big power cars (750hp+) but for upto 750, the 2.75" is fine.

For you going forward, if you really want to press ahead with this, go for the 2.75" Milltek decatted downpipes and ask your exhaust Shop to make them fit to your Akrapovic. They will make a new flange or some sort of sleeve that will mate the two up. You'll still gain a whack of power but just not as much as a full Milltek exhaust would for the reasons mentioned above.

Very informative post Leo That's why I chosen Miltek non resonated version (less restrictions than akrapovic exhaust system), I always can do ecu remap and get nearly 700 hp with my stock downpipes and my none resonated Miltek, sound is awesome and not too loud, if I want more power I can always add Miltek cattles downpipes and get 750+ But I think sound is too loud

Plus stock downpipes fit just fine Miltek exhaust system

[DXB_RS6]

Thank you both for taking the time to give such a detailed posts.

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