Project S4: Milltek Sports Exhaust system

Replacing your standard exhaust for an aftermarket performance exhaust system on any turbocharged car is a superb way of reducing turbo back pressure and increasing gas flow – liberating power, reducing turbo lag and improving throttle response. It also often saves weight, so there are gains to be had all round.
I have replaced more exhaust systems than I care to remember – especially on my turbo nutter barges – always with good results, but none better than with systems from They may not be the cheapest, but you get what you pay for: Quality.
Milltek Sport’s 304 aircraft-quality, mandrel bent (smooth, for best possible gas flow), stainless steel systems have a genuine performance edge – power gains around 10%, sounds that are truly awesome and styling that is subtle but sexy – making them the ideal choice for my stealth bomber B5 Audi S4. As they say themselves: “Performance that blows your mind, not your ears!”
Your original catalytic converter will typically have 400 or 600 cells per square inch (cpsi), which restrict gas flow, typically allowing an open area of around 55-65%. Replacing these with Milltek Sport Hi-flow Sports Cats (fully integrated into a large bore downpipe), with either 100 or 200 cpsi creates an open area of 75-85%, hugely reducing back pressure and increasing gas flow rates. This is all very desirable for extracting more performance, especially on turbocharged engines, like my S4’s 2.7-litre twin turbo V6.
There were a number of options available to me for the S4: Hi-Flow Sports Cats on their own, 100-200 cpsi. Cat-back systems with the Sports cats, or maintaining the OE cats and in 2.25-inch or 3-inch. Then there was “the daddy” – dual 2.25-inch full turbo-back system, with dual Milltek 100 cpsi Hi-Flow Sports Cats, LH and RH downpipes & link pipes, centre section, rear silencer and special, 76.2mm twin tailpipes. Naturally, I had to have the beast.
Unpacking it at Henstead Motorsport (01502-714177) was better than Christmas! Compared with the heavy, narrow gauge, twisty OE system, it’s a real work of art – beautifully designed, light, shiny and brilliantly engineered. And, despite the fitment being a relatively awkward/time consuming job (as you need to pop the nearside driveshaft out to fit the LH downpipe), the actual fitment of the Milltek system was a piece of cake. Everything slotted together perfectly, which is definitely not the case when you buy other well-known aftermarket exhaust systems, believe me. They often need modification to fit. Not Milltek Sports. Spanner supremo, Dave Green of Henstead Motorsport loves them – and so do his knuckles. No skin loss here. Just nice and easy fitment. Job done.
Firing it up was a real treat too. The OE system is sooooo quiet on the S4, you can hardly hear the meaty V6 at all, let alone the turbo boost. But the Milltek changed all that – to just the right degree; not at all intrusive, but certainly adding character – making the twin turbo V6 come to life; burbling with intent at tickover.
The real deal though is the performance gain on the road, which is palpable, even before I dyno it and I’d say 10% is a conservative estimate to the gains. Throttle response is massively improved, the tiny twin turbos spool up noticeably faster and the V6 revs truer, for longer; hunting out the rev limiter with a definite gain in low-down torque, mid-range punch and top end power. It’s bleeding marvellous: Subtle, sexy and swift, just like the S4.
It looks fabulous too, and is so much lighter than the standard system, there’s an additional performance gain. And, best of all, just like the S4 itself, the new Milltek Sport system is a real Jackyl and Hyde… quiet and refined when you are pottering, but coming instantaneously to life, with real character, pace and class when you nail the throttle. Absolutely spot on…
I am very much looking forward to strapping the S4 onto the dyno now and seeing what grunt it produces, and at what rpm Vs OE, then re-mapping the Superchips ECU with Rich from Viper Tuning, to maximise the gas flow gains from the Milltek system.
Milltek have 20 years experience in the exhaust game, manufacturing superb systems for key brands like Audi, VW, BMW, Porsche, MINI, Subaru and Mitsubishi – all with a loyal tuners’ following, and deservedly so. Once you have had a Milltek Sports system, you’ll never want another brand. Bravo Milltek!

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