Pipe Dreams....................................

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


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.


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.

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