They’re the most common performance mod we make to our bikes, but are aftermarket exhausts still worth the wedge they cost?
It’s ironic when you think about it, but nostalgia is bigger now than it’s ever been. Old cars, old bikes, old politics even – they’re all making a comeback. And while it’s true that a lot of stuff from the past was a bit crap (Reliant Robins, R65 BMWs, rickets), a lot of stuff was also really brilliant (Cosworth Fords, CB750 Hondas, Concorde). And in many ways, tuning a bike was easier, simpler and more fun back in the day. That’s mostly because the bikes of the time were a teeny-weeny bit shite as standard. The bike firms were doing great work producing sweet machines like the Kawasaki GPZs, Yamaha FZRs and Suzuki GSX-Rs of the 1980s and 90s. But they were far from perfect, and there was a lot of scope for the aftermarket guys to make them much better. Even in the late 1990s and early 2000s, as bikes moved on, it was still possible to bolt on a performance pipe from someone like Yoshimura or Micron and add 20-odd bhp, plus a heap of torque, to your litre sportsbike.
But now, it’s all got a bit trickier. The bike firms cottoned on a long time ago that if they put a bit more effort into their exhaust designs, they could ratchet up the grunt on their motors, making their bikes even more crackers than the competition. So where in the dim and distant past, they’d just weld up some old steel tubes into a basic drainage system to keep the superhot exhaust gasses away from your feet, nowadays, a top-spec superbike has a fiendishly complex system of
header pipes, pre-catalyst sections,
underslung silencing chambers and natty little MotoGP-style end cans. Computercontrolled butterfly valves open and close at carefully-chosen rev points, boosting power at the necessary times. With all this in mind, it begs the question of how can the aftermarket lot compete?
Law and order
Well, luckily for the performance kit makers (and us!), the manufacturers also have to jump through a series of ever-stricter hoops these days. Much of that is down to European emissions regs, which are there to stop kids and old folks being poisoned by nasty gasses like CO, NOx and HC. Now that’s a fair shout – no one wants their granny or kids dying from asthma caused by traffic pollution. You could, of course, argue that bikes being such a tiny part of road traffic means that these rules are overkill. But they’re the rules we have to play by.
And Britain leaving the EU is unlikely to change that either – air pollution doesn’t play well with voters, so expect UK law to stick closely to the EU regs here (and bike firms will probably still just make one main bike design for the whole of ‘Europe’, including us troublemakers, anyway).
So, when bikes come from the showroom nowadays, they’ve got an incredibly high-tech solution in place, aimed at giving the best possible power. But – those systems have to make not one but two major compromises. They have to do the emissions thing, cutting out the nasties in the exhaust gasses and the excess noise. Plus, they have to keep the bean counters in Japan (or Italy/ Germany/Hinckley) happy. Bike firms are there to make a profit at the end of the day, and production costs will limit the design and materials used for each component, including the exhaust system.
There are other compromises too: quality control and longevity requirements mean an exhaust has to be made tough enough to cope with the worst possible conditions. A stock pipe might have to deal with tens of thousands of miles in the baking hot deserts of California, as well as the soaking saltstrewn roads of a British winter, and the freezing temperatures of Scandinavia. If it collapses after a couple of years of this, you’ll have a load of pissed-off punters, and a heap of warranty claims. The fact that most folk buying a GSX-R1000, say, will toss the heavy, welded, thick stainless-steel system into the back of the garage in favour of a race system doesn’t excuse the manufacturer from having to make a pipe that’s fit for purpose in the first place. Which generally means a good five years’ service, minimum, in all the conditions it might meet around the world.
Exhausting all options
Can you see the gap for the cunning aftermarketeers then? If they’re able to bypass some of those compromises, they can make gains in areas that aren’t open to the factory engineers. If they can use materials like Inconel super-alloys, titanium or carbon fibre, which the spreadsheet jockeys have banned from the production line on the basis of cost or faff, then their pipe can lose a load of weight. Ditto if they lose EU emissions compliance, for a track bike, or for sale in a market where this isn’t essential for the end user. The UK is a good example here – the motorcycle MOT doesn’t check for gas emissions, so a bike will pass its annual roadworthiness check (after the first three years) with a non-EU4 system in place. It’s a bit of a grey area in truth, but the essence is that the manufacturer has to meet certain rules to sell a bike, which the user doesn’t necessarily have to comply with.
“The good thing for us is we are not subject to the Euro 4 restrictions,” Rich Austin of UK exhaust maker Austin Racing told us. “So anything goes – we can push the boundaries with our technology. When we are subject to Euro 4 we will still keep doing what we do but also add an additional range for that.”
Colin Peabody imports Akrapovic, Yoshimura and Remus pipes into Britain – so he knows all there is to know about bike exhausts. “The manufacturers have to work really hard to meet the regulations, hence we now see huge restrictive silencers – just look at the GSX-R1000. This gives more opportunity for aftermarkets to deliver a tidier, lighter, better-looking product that can deliver more power and, if it’s a race exhaust, more noise.
“Not every market adopts E4 compliance. So exhaust manufacturers that operate on a global basis such as Akrapovic, Remus and Yoshimura are now producing E4 compliant products for the tightly-controlled EU markets and an ‘open’ or ‘race’ product for markets where E4 means nothing. Many markets in Asia, South America, and Southern Europe either don’t care or don’t implement Euro 4 standards so the exhaust manufacturers need to service those markets too and make variants that are less restrictive and smaller/lighter/noisier. However, to make a fully Euro 4 road legal compliant product for the main European markets is hard and requires skill and technology to improve on the OEM exhaust.”
So there you have it. Pipes are complicated – and getting more so. But there’s no need to go on about the good old days like a mad nostalgia-fiend banging on about your GS1000 with a Micron 4-into-1. There are still loads of ways to get a sweet system on your bike, with better sound, less weight and (most importantly) a barrowload more bhp. Plenty of specialist companies are still pushing the boundaries in emission exhaustion on the race track, with the technology being passed over to road going products in due course.
Racing to the future
SC Project from Milan in Italy is a major pipe maker and supplier to several teams in MotoGP, Moto2, Moto3 and Superbike racing. Since 2016 their top technical man has been Paolo Termignoni, the son of Luigi Termignoni ( of legendary exhaust firm… Termignoni). He works closely with founders and head guys Stefano Lavazza and Marco De Rossi (who formed SC in 2005), and went on to give us some real insight into how some of the highest level of contemporary performance exhausts are made these days.
“The design of our exhaust systems is developed by our R&D department which makes 3D designs; then a prototype is made by a 3D printer and after several tests, the series production can start. The design of the exhaust system is fundamental when making the prototypes for the different categories, from Moto3 to Moto2 and Supersport up to World Superbike and MotoGP where we are the Repsol Honda HRC partner.”
Asked about how SC-Project works with teams, Paolo went on to explain, “SC-Project has been producing exhaust systems for MotoGP for years. We started in 2009 with Team Pramac Ducati and we were their supplier for the five years after that. Later we have supported otherMotoGP teams, like Team Aspar Honda, Team Gresini Honda, Team Avintia, Team PBM, L’AB Cardion and more, and in 2017 the Team Marc VDS and the official Honda HRC.
“Inmost cases wewill develop a system in situ on a racing bike, to ensurewe not only get the best power, but the best fit. All the testswe do for newsystems are done in Japan, with collaboration between SC-Project and the official and unofficial teams being both direct and strictly confidential. Inmost instances at aMotoGP levelwewill work with a team’s specific demands to produce a system that meets their requirements, but in the lesser championships our involvement is much more free. In SBK, Moto3 and Moto2, the development is fully realised by our race department without any collaboration with the companies. Systems are of our own thinking and design, which we then produce and pass on to those teamswe choose to work with.”
Metal and more
As you can imagine, SC- Project and many other premium exhaust manufacturers use some pretty trick products to make their systems, factoring in both performance and weight at the top of the agenda. One of the specialist substances found in exhaust manufacturing is carbon fibre – although it’s less popular than it used to be. Carbon fibre (CF) is a composite material, made up of (yes!) carbon fibres, woven into a sheet of cloth-like material, then formed into a ‘matrix’ with tough resins (fancier versions of Araldite, basically). The trick here is that the
carbon fibres are very strong in tension – you can’t break them if you pull them end-to-end – and the resin is very strong in compression – you can’t break it by squashing it really hard. So they complement each other, like steel reinforcing bars in concrete.
The bonus is that carbon is very light, so you get a stiff, strong, light material, which can be made in a wide variety of forms. The downside is that it’s pricey and labour-intensive to make, so isn’t suited for enormous production runs. The resins also need to be specially selected to resist the heat in an exhaust application, and the UV rays in sunlight, or they go all yellow and nasty as they age.
Titanium is one of the sauciest metals around, and much loved by aerospace engineers. It’s not easy to work with though, so most titanium tech is, in fact, rocket science. Its USP is that it’s very light, yet very strong, and it’s also very corrosion-resistant. So in theory, it should be the perfect replacement for steel in exhausts – and there have been a load of titanium pipes on bikes over the years. The downsides aren’t insurmountable: it’s a bit trickier to weld than steel, and if you don’t get the alloys right, it can be brittle and prone to cracking. It’s pricier than steel of course, so you tend to see it only on primo bikes – the latest GSX-R1000 has a titanium muffler, as did the legendary K5 version of the big Gixxer.
Finally, comes Inconel. This is an unusual alloy in bike exhaust design, because it’s really expensive to buy and very fiddly to work with. It’s one of the metals developed by British boffins when they were building the first jet engines in the Second World War, made up mostly of nickel and chrome, with a load of other trace metals added to the mix for different applications. It’s really good at resisting heat, and stays strong at mega-high temperatures (like inside a jet engine). That means you can use very thin walled tubes in an exhaust, for super-light weight, yet keep all the strength you need. It’s a speciality of the Formula One world, and UK pipe maker Austin Racing makes much of its Inconel use, tapping into the UK’s F1 industry to make lush bike exhaust systems.
Can vs system
Back in the day, bike header systems were dead simple – just tubes to carry the exhaust gas flow back to a single silencer hung off the pillion pegs. All the work was done in the big old can (think back to a Kawasaki ZX-12R or the like), so if you whipped it off and swapped in a pukka race silencer, you could get big changes in the engine output.
Now though, the bike manufacturers have had to get working on the gas flow as soon as it comes out of the exhaust ports. They’re using cross pipes in the header pipes to link cylinders together, with butterfly valves in there to alter the flow at different rpm. Then they’re putting catalytic convertors high up in the system, closer to the combustion chamber. That means the convertor gets hot quicker when the engine is started, and can get to work cleaning up the emissions
BIKE HEADER SYSTEMS WERE DEAD SIMPLE – JUST TUBES TO CARRY THE EXHAUST GAS FLOW BACK TO A SINGLE SILENCER HUNG OFF THE PILLION PEG.
sooner (it needs to be red-hot to break up the polluting gasses into harmless products).
The trend for mass centralisation has driven attempts to tuck the main mass of the exhaust underneath the engine, so you get a big silencing chamber below the sump rather than hanging out the side of the bike. In the end, the silencer can has become little more than the finishing touch to an exhaust system – late 2000s bikes like the GSX-R750 only had a small side-mount end can.
That’s good for stock performance – but it means that simply replacing the end can on its own doesn’t make the big differences it used to. “Slip-ons are really about looks and weight saving, with around 3-5bhp bolt on power gains,” said Rich Austin. Not all bikes are like this though. “Some slip on kits still reveal a big power increase and weight saving if the cat converter is in the silencer,” said Colin Peabody, boss of the UK Akrapovic, Yoshimura and Remus importer, Performance Parts Ltd. “So simply fitting a slip-on can give a big increase still.”
And Peabody reckons there are still easy ways to get more performance from the newer models. “There are the ‘three-part systems’ bikes, with header, mid section and silencer, such as the ZX-10R or R1. Here, the big gain comes from removing the centre section containing the catalytic convertor, and then swapping the silencer too, so there’s still no need to change to a full system. They are often called ‘half systems’ and bikes like the ZX-10 respond very well to this.”
But for the best peak performance results, replacing the whole shooting match is still the best bet. Letting someone like Yoshimura, Akrapovic, SC-Project, Arrow or Austin take over from the engine back means all the compromises made for OE production are binned. You can use bigger header pipes to give maximum peak gas flow, completely lose the catalytic restrictions, and drop restrictive butterfly valve systems altogether. “Ultimately,” said Colin Peabody, “the best results will always come by swapping to a full system. The GSX-R1000 is a good example of this – the new 2017 bike gains over 10bhp with a full Akrapovic or Yoshimura system fitted.”
The technical bit
So with so much on offer, it’s only natural to question how it is that exhausts make such gains for your bike’s output? Surely you just need some way of getting the exhaust gasses out of the motor as quick as possible, to stuff more petrol in? Well, yes, and no. The performance aspect of exhaust design comes from management of pressure waves within the gas flow. Every time the exhaust valve is pushed open by the camshaft, it releases a small explosion into the header pipe. That explosion is a sound wave, essentially, and it moves down the pipe at the speed of sound (around 770mph at room temperature, about 1000mph at engine temperatures). Now if it just ended at an open pipe, the wave would explode out of the end (hurting your eardrum), but that also makes a (weaker) negative pressure or vacuum wave travel back up the pipe again towards the engine, again at the speed of sound. If the timing is right, and the negative wave hits the combustion chamber when the exhaust valve is open again, it will help suck some of the exhaust gas out of the valve port, improving the combustion process and boosting torque.
Much exhaust design is therefore about managing these waves inside the system, to do good things at the right time, and minimise the bad things. Linking cylinder header pairs lets you use the pressure wave of one cylinder to help another, and fourinto-one layouts boost peak power, while four-into-two generally give more torque.
In the old days, performance pipe making was about trial and error – but now, computers can help with a lot of the theory, telling engineers what lengths and sizes of tubes and chambers to go with, for the desired power and torque, and sound/ emissions compliance. Through using such systems, manufacturers can determine the exact diameters, curves, lengths and link pipes needed to maximise gas flow and improve engine performance. That’s a privilege that simply wasn’t around in the good old days, or at least not on such a broad scale. Through fancy software and even fancier production techniques, exhaust companies can now make inconceivably great systems, that not only boost power, but sound as though they’re straight out of GP. In essence, if you were ever to debate whether an exhaust was still an essential/viable addition to your motorcycle, the answer would be YES! As to how much of a gain you’ll notice, that’s all down to spec, mapping and whether you remembered to bolt the system on properly or not. But in reality you should at least expect to save weight, get a fancier finish and find a few more ponies in the process. Especially so if you can bin off one of those life sucking catalytic converters.
SIMPLY REPLACING THE END CAN ON ITS OWN DOESN’T MAKE THE BIG DIFFERENCES IT USED TO.
This lot’s destined to grace some of the fastest bikes on the planet. You need a full performance system for the biggest gains.
3D scanners are used to aid the design and fit of systems. MotoGP bike exhaust tech trickles its way down onto production bikes. Carbon fibre is a popular choice is exhaust production.
It’s not just a pretty sight. This SC Project system saves precious weight and cranks performance levels.
Fagan looks so much prettier with a mask on.
Loud, proud and packing a punch... Stock systems strangle engine performance.
Modern tech takes the guesswork out of exhaust design and performance.