Audi S3 Stage 3 best exhaust systems performance wise?

S3 W

Registered User
Hi currently have a stage 3 in for custom mapping & was told the rear Miltek Catback (Resonated) was restrictive. Advised to replace for BCS full system.

Popular opinion is that BCS systems are the best performance-wise followed by the Milltek etc, which I agree however did not see the need for a new BCS system assuming my 3" DP decat joined to a 2.75" miltek cat-back is sufficient for up to 450bhp based on the fact that there's a TTE420 thread with over 30 stage 3+ cars with briefly listed mods for each car, almost half of the cars have Milltek exhausts in the list (assuming only cat-backs) and achieved 400-450 bhp.

Just wanted to see some opinions/experiences to why people think these are restrictive & if so what Miltek systems do these TTE420 cars have? last I knew for the 8P S3, MK6 R & GTI. Miltek only offer two variant (Resonated vs Non-Resonated) systems that all share the exact same rear box MSAU346 which is claimed to be restrictive performance-wise?

Please keep the discussion based on the performance aspect of the exhausts & not the sound.
 

prt57

Registered User
I follow the FB posts on RTech and I am sure recently there was post where the Milltek was holding back the power. Like you, I only know of 2 x Milltek variants.
With the BCS they will not do a non valved system for an S3, or at least they did not at the end of last year.
When on boost above 8psi the valve in the left rail pipe opens in the Powervalve system and the back box is bypassed. So the exhaust gas is only going through the Siamese silencers under the car therefore not very restrictive. The WRC version does away with these Siamese silencers and so when the valve opens there is no restriction back from the cat or decat.
It’s strange really as APR are quite happy keeping the standard catback in place with their downpipe fitted to a TTE420 to reach at least 400 BHP and I chatted to a tech at Awesome who said they achieve maybe 417 BHP really.

At the end of the day, your custom mapper will do the best with the hardware you provide and whether it is worth the vast expense of a totally new system for the sake of a few BHP or Ftlbs. You may not feel the difference on the road in the real word anyway. 10 BHP increase at 400 BHP is only 2.5%.
Also BCS or Trackslag do a 3.5” downpipe which really helps the gases exit with a hybrid. A TTE 420 would not be going above 420 BHP really if the mapper was trying to preserve your hardware so you could be OK anyway.
 

S3 W

Registered User
I follow the FB posts on RTech and I am sure recently there was post where the Milltek was holding back the power. Like you, I only know of 2 x Milltek variants.
With the BCS they will not do a non valved system for an S3, or at least they did not at the end of last year.
When on boost above 8psi the valve in the left rail pipe opens in the Powervalve system and the back box is bypassed. So the exhaust gas is only going through the Siamese silencers under the car therefore not very restrictive. The WRC version does away with these Siamese silencers and so when the valve opens there is no restriction back from the cat or decat.
It’s strange really as APR are quite happy keeping the standard catback in place with their downpipe fitted to a TTE420 to reach at least 400 BHP and I chatted to a tech at Awesome who said they achieve maybe 417 BHP really.

At the end of the day, your custom mapper will do the best with the hardware you provide and whether it is worth the vast expense of a totally new system for the sake of a few BHP or Ftlbs. You may not feel the difference on the road in the real word anyway. 10 BHP increase at 400 BHP is only 2.5%.
Also BCS or Trackslag do a 3.5” downpipe which really helps the gases exit with a hybrid. A TTE 420 would not be going above 420 BHP really if the mapper was trying to preserve your hardware so you could be OK anyway.

Thanks for the info, seems like Milltek system is probably restrictive due to high EGT at the downpipe. EGT can get very high at full throttle for extended periods which is where the BCS system has the major advantage with a better flow keeping the EGT down.

I will be going for the BCS eventually to see what difference it has over current exhaust setup as for now once I get the dyno prints will confirm power data with the existing exhaust.

For reference TTE420 can achieve more than the 420 bhp reliably, TTE themselves have said that it is 420ps+ capable but I'm assuming to an extent, seems that 420-440 is acceptable any more than that would possibly be overkill.
 

paddy

Registered User
I would be very surprised if the stock system was that restrictive. I was told by APR that the std 8p S3 system (cat back) is so good they dont even bother to make an upgrade, they said just change to the 3" cast down pipe and sport cat. Its very easy to fall for all the hype on these things and go for the "in" part but very questionable whether its actually worth it. Personally if i was about to spend £1200 on a BCS i woulds want to see some serious proof they actually improve performance. Ask them if they have the before and after test dyno results for their systems.
Its very easy to claim a system is less restrictive but trying to get some facts and figures from performance part manufacturers s not easy ..... :)
 
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steviedee

Registered User
Im running a BCS downpipe with a 200 cell sports cat and standard Audi back box, running a TTE420 hybrid with APR map and the dyno says 420bhp/430lbft torque (Ecotune Glasgow)

I really dont think a full system would give much if anything! The car goes like stink and I`m happy :rockwoot:
 
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