EXHAUSTS AND THE aftermarket: why bother? Manufacturers now expend tens of thousands of hours and millions of pounds developing their performance cars to a high state of tune, and the exhaust system is critical to that process. Can the aftermarket really do better?
Well, the aftermarket exhaust industry has come a long way since the days when it simply created nice shiny systems out of stainless-steel tubes, said they’d last forever and give you lots more horsepower, and ensured they made plenty of noise to drown out the sound of often empty promises. Reputable aftermarket firms today have to comply with EC regulations concerning sound levels, exhaust-gas emissions and manufacturing standards, and employ university-educated engineers to operate sophisticated design software to create their products.
The goal of any aftermarket exhaust system is, you’d think, to hurry the exhaust gases away from the combustion chambers quicker than the original-equipment (OE) system can manage. The faster the exhaust gas is evacuated, the sooner a fresh fuel-air mix can be injected, and the more power and torque can be produced. To this end, aftermarket systems try to follow a neater, straighter path from manifold to tailpipe, and courtesy of more laborious and costly bending and welding processes, the internal surface of their pipework is smoother, for unimpeded gas-flow. They also feature expensive high-flow catalytic converters, and their silencers breathe more freely.
And yet few aftermarket manufacturers make a song and dance about power-increase claims, even those such as the Slovenian maker Akrapovic, or the UK’s Milltek Sport, both of which are also heavily involved in motors port. Akrapovic does mention a 14bhp boost to the power output of the BMW M2 by using its replacement downpipe and sports cat, but you have to read a long way through the product description to discover that fact. It’s as though the industry is nervous that any increases may not be repeatable.
Quicksilver’s managing director, Paul Goddard, is equally coy about highlighting power improvements, and claims his clients have other priorities. “Customers with expensive sports cars tend to be extroverts with an emotional attachment to their cars,” he says. ‘To them, sound quality is critical; their car is already quick enough. So our systems are tuned to emphasise and amplify the aural sensations of the exhaust. Sound helps you judge your car’s performance.’
That last comment is particularly pertinent in an era where downsized engines with turbochargers are being criticised for weak aural performance -the Porsche 718 series is a prime example. Aftermarket silencers can help restore some of the roar emerging from the tailpipes, and turbocharged engines can respond well to aftermarket downpipes used in tandem with sports cats, with [again, largely unspecified] improvements to power and torque. The increasing popularity of ‘switchable’ exhausts, which allow cars to meet noise constraints in urban areas but achieve the full banzai out on the open road, are testing the ingenuity of aftermarket engineers. Not least because the controls for these systems can be deeply interlinked with the rest of a car’s electronics.
Milltek is working on a valve arrangement that opens progressively rather than turning on and off, and Quicksilver has developed a system of ‘balance’ pipes that are brought into play depending on engine speed and throttle opening, creating a smoother change in tone [DB11 system pictured, left]. Meanwhile, Akrapovic has put control of valve-switching in the fingertips of the driver, with a wireless push-button. Whereas stainless-steel systems were once the preserve of the aftermarket, they’re now far more commonplace as an OE fitment, so the aftermarket has had to move on to new things. Stainless steel does still feature in their brochures but is of higher-grade metal, while the tubes themselves feature thinner walls to reduce weight. In recent years, though, titanium has come to the fore for lightweight systems, spearheaded by Akrapovic, which has an in-house titanium foundry [and whose Ti hardware for the Ferrari 488 GTB is pictured above].
Titanium yields massive weight savings, particularly for silencers -a titanium silencer for the Audi R8 can trim 30kg from a 45kg OE item. The technology and experience available to the major aftermarket-exhaust manufacturers have now caught the eye of mainstream car makers, some of which are calling in this outside help. Porsche, for instance, had Akrapovic develop the OE system for the 997 GT3, and Volkswagen recently announced a collaboration with the company for a titanium sports exhaust for the Golf R – it’s 7kg lighter than the standard system. Akrspovic is also a motors port partner to BMW and collaborated with Audi on its World Endurance Championship campaign. Quicksilver, Milltek and others also have manufacturer motor sport connections. So, the industry has turned full circle, with the aftermarket makers now not merely being tolerated by car manufacturers, but in some instances being embraced.