All you need to know about
EXHAUSTS What you need to look out for when youâ€™re choosing and fitting a non-standard end can, and what difference you should expect it to make Words Benjamin Lee Pictures Jason Critchell and Matt Hull
How to fit an end can 1
Let a hot exhaust cool before trying to remove it. Loosen the exhaust mount bolts and the link pipe clamp. Penetrating oil can help with rusty fastenings.
Two aftermarket cans ready for dyno testing. Both the Yoshimura the Remus offer more power than the stock exhaust
WHY FIT AN AFTERMARKET CAN TO MY BIKE? Standard exhausts are designed specifically for your bike. They keep the noise to an acceptable level, they often have catalytic converters built in, and they should last the lifetime of the bike. But they are often ugly, heavy and sound muted, due to ever-tightening noise regulations. But either way, a lot of us like to put a personal signature to our bikes and a different end can helps it to stand out.
WHAT TYPE SHOULD I GO FOR? Within reason go for whichever one you like the look of. There are many different makes of exhaust and even more different styles available. They can be made from aluminium, titanium or carbon and can be round, oval or conical in shape. Despite what they look like from the outside they are all similar inside: a perforated tube allows the sound waves to bounce into glass fibre matting to quieten the noise. This provides a freerflowing exit for the gases than you get with original exhausts, which send gases back through extra chambers in the silencer to help lessen the noise. Go for a style you like, but some may not be suitable for your model so chat to the manufacturers or have a look at their website. Also, the smaller the exhaust the more noisy it’s likely to be. This could get annoying if you tour or cover lots of miles and it could lead to regular stops by police.
WHY DO SOME EXHAUSTS SAY ‘ROAD LEGAL’? The Vehicle Certification Agency admit the exact rules applying to modified exhausts are complicated, but here are the main points. Silencers are either stamped as road legal or declared ‘not for road use’. The police can pull you over for excessive road noise, and if your exhaust is stamped ‘not for road use’ expect to pay a fine. To be road legal, any exhaust used on a motorcycle produced after February 1997 has to display a ‘BS AU 193a: 1990/T3’ mark, or an ‘E’ mark, or an equivalent international standard marking. This shows the exhaust has been tested by the manufacturers on that particular type of bike and has passed a static and drive-by noise test to make sure it conforms. MoT testing also incorporates an exhaust assessment. A decibel test will be carried out, and the tester has |
discretion to decide what passes and what fails. The tester will also check whether the end can is road legal. There is currently no test on motorbikes for emissions, so if you’ve removed the catalytic converter it’s OK. Some exhausts come with removable baffles. These are usually tubes with holes drilled in and are screwed or riveted into the exit of the can. They bounce some of the sound waves back into the can to reduce the noise to a legal level. Removing the baffle doesn’t make the exhaust illegal because the E mark is on the exhaust.
If your bike has an exhaust valve, the link cables that run between the valve and the servo motor have to be removed. Detach the motor and undo the link cable ends.
WILL A NEW EXHAUST DEMAND OTHER MODS? Most exhaust manufacturers say you don’t need to adjust your bike after fitting one of their exhausts, and fitting it won’t harm your bike. But your new exhaust is a straight-through design and the gases can now exit more easily so you’re changing the exhaust back pressure. This will free up more power towards the top of the rev range. At lower revs and part throttle less back pressure can sometimes cause a change in the behaviour of your bike, such as a lumpy idle. Giving the exhaust gases an easier escape route also leans your air-fuel ratio (or AFR). An optimum ratio is 13.2 parts air to one part fuel; a leaner mixture will make more power but will make the engine run hot and snatchy through town.
TESTING THE THEORY We want to find out how easy it was to fit an exhaust end can, what difference it made to the power delivery and how the bike ran afterwards, so we go to a dyno centre with a standard Yamaha FZ1 and two aftermarket exhausts with link pipes: a Yoshimura TRC (£240) and a Remus Okami (£290). Dyno centres measure the power and torque of a bike by strapping the bike down so it can’t move and sitting its rear wheel on a drum that offers resistance as that wheel’s turning. The dynamometer’s computer then measures how much the bike fights the resistance as it turns the drum, giving a power curve throughout the rev range. The first dyno run with the standard Fazer yields solid results: a smooth curve of power with a kick at 7000rpm and a maximum of 131.3bhp at 11,500rpm. The increase in bhp between 7000rpm and 8000rpm is perfectly placed to give good overtaking power right
where riders need it. The standard bike returns a 12.7 average air-fuel ratio, which dyno operator Steve tells us is slightly rich for safety and smoothness, and is perfectly acceptable. We now have our base line. We’ll compare the Yoshimura and Remus cans and we’ll also test the difference between baffled and unbaffled exhausts. Taking the stock exhaust off is straightforward, although disconnecting the EXUP valve is fiddly. With the exhaust in our hands, the first things we notice are its substantial size and cheap paint job. This is a heavy piece of kit, at 5.5kg. Both alternatives are much lighter, chopping kilos off the FZ1’s weight. We fit the Yoshimura TRC first, and it’s a pretty piece of work. It’s obvious the Yoshi is lighter and more attractive than its predecessor, but how will it fare on the dyno? Steve presses the ignition, and it’s as if a totally different bike bursts into life. The Yoshimura produces a firmer, more rumbling exhaust note down low, that rises to a fantastic fever pitch at the red line. Steve nudges the limiter and lets out the throttle. A few dyno runs later and we have our first round of results. We remove the end can’s baffle and run the test again. Steve brings up the results on a computer screen. It’s a graph with the stock exhaust as a baseline, and the baffled and unbaffled Yoshimura results displayed alongside. All three lines follow a similar shape: the kick of power at 7000rpm is still there, and power continues to rise to 11,600rpm. In both cases, the aftermarket exhaust provides more power than stock,
Dyno run showed the Remus Okami improved power delivery, even with the baffle in place
Slot the new can onto the header exit pipe and seat it home. Some link pipes will need to have a new gasket fitted, others may need exhaust paste to make a seal.
Adjust the new exhaust’s mounts to match with the fixings on the bike and bolt them together.
Ensure the link pipe clamp is tightened over the cutaway to give a close fit with the header exit pipe. FEBRUARY 2013
I’ve got the power bug… what can I add?
Power Commander can alter the fuelling to help eradicate flat spots
Yoshi connecting pipe has a small silencer built in yet still makes more power than standard
■ DE-CAT PIPE Simply a pipe that is put in place of the catalytic converter on some bikes. It has a questionable impact on performance, but saves weight. Expect to pay £70-£100. ■ AIR FILTER A freer flowing air filter is an easy modification, but with modern bikes being so efficient it won’t add lots of power. They cost around £50 but can be cleaned instead of being replaced. ■ DOWNPIPES Changing the downpipes and exhaust for a full race system could net more power but will need to be set up properly – fuel-injected bikes will benefit from a Power Commander and carbureted bikes will need rejetting to suit. Budget £1000 for the system and around £500 for a Power Commander and dyno time. ■ VELOCITY STACK Changing the velocity stacks, the bell-shaped devices that supply air to the injection throttle bodies in the intake system, can lead to a high-end performance boost, but this comes at the expense of mid- and low-range power. ■ INSURANCE You will need to tell your insurer if you have modified your bike in any way. An exhaust will rarely affect the policy, but any further mods may well increase the cost.
even from a lowly 4500rpm. With the baffle in place, the Yoshimura keeps a steady 3bhp stronger than standard from 7000rpm. Remove the baffle, and power rises a hearty 8-10bhp above stock, from 8000rpm up. Air-fuel ratio is leaner. An average of 13.1 AFR is closer to the optimal 13.2 than is the standard can (12.7). The unbaffled Yoshi adds an impressive power boost at the top of the rev range. This is good news, but while we install the Remus Okami, Steve tells us there’s another side to the story: “When tuning a bike, it’s important not to focus solely on chasing more top-end power. Flat spots will hinder good control at lower revs and on the road. After all, road bikes spend the majority of their time below 7000rpm, so the low and midrange of the engine should be reliably smooth and not over-responsive.” The Remus end can is also much easier on the eye than the dirty great lump of a stock exhaust, but we agree that the black plastic end cap loses out to the Yoshimura’s stainless steel offering. Its deep bass idle is stronger than the Yoshi’s, but we think it lacks fizz up in the heady heights of five-figure revs. After a few trips to the red line and back, Steve brings up results for our second slip-on. This time the shapes of the power curves are strikingly similar to stock performance. Baffled, the Remus delivers 2-3bhp more than the standard exhaust from 6800rpm, widening out to a 5bhp difference between 10,000 and 11,000rpm. The unbaffled exhaust follows this pattern almost perfectly, maintaining a 2-3bhp lead above the baffled Remus from 6800rpm. However, with this power increase comes a lean 13.6 average air-fuel ratio in lower revs that could lead to a snatchy throttle response at normal road speeds.
WHAT POWER DIFFERENCE DO THEY MAKE?
Based on our dyno results, the unbaffled Yoshimura produces the most power, with 138.2bhp at 11,500rpm, and 71.4lb.ft torque at 7700rpm. The unbaffled Remus is not far behind, with 137.5bhp at 11,500rpm, and 70.1lb.ft torque at 7800rpm. You can expect similar results from other manufacturers’ exhausts. Both exhausts are noticeably louder without their baffles. This may or may not bother you but on the track it could lead to the bike failing the noise test and if used for commuting, or kept at home within hearing distance of neighbours, a loud exhaust could be seen as anti-social. Both baffles do a good job of cutting down the decibels without losing the characterful exhaust notes, and we’d keep them in.
It’s important not to focus too much on chasing more top-end power. Flat spots will hinder control on the road HOW MUCH DO THEY COST? A regular round or oval exhaust in stainless steel can cost as little as £100, but look at the quality before you buy. This is easy as there are several very good UK manufacturers you can visit (see below). If you start looking at titanium and carbon fibre exhausts or fancy shapes then expect to pay more. Beware of unbranded exhausts; we’ve seen one from China shoot its innards out of the back after a couple of hours’ use. The tests involved in getting an E mark are prohibitively expensive, which stops some makers getting them tested. So they may be quiet, but without the stamp they’re illegal all the same.
WHAT IS A POWER COMMANDER? Our Fazer gives textbook results. As standard it has a smooth power curve. A baffled aftermarket exhaust gives more power and an unbaffled one gives yet more, but it neither introduces any flat spots nor leans the mixture to a dangerous level. Be aware that some bikes may behave differently and adding a new exhaust could change the power curve or even introduce flat spots. If this is the case, you may need to go to a Power Commander or similar device. These cost around £350 and piggyback the ECU, adjusting the messages going from the ECU to the injection system and allowing you to download modified fuel maps for your modifications or to build your own custom map for your bike. It can iron out inconsistencies in the power curve that an aftermarket exhaust system could create. However, it’s an expensive piece of kit, and usually not needed for bikes with only a slip-on exhaust.
Yoshimura www.performanceparts-ltd.com Remus www.performanceparts-ltd.com Scorpion www.scorpion-exhausts.com Beowulf exhausts www.beowulfuk.com Power Commander www.dynojet.co.uk Juicebox fuelling, TBR exhausts www.juicypipes.com Arrow exhausts, Pipercross air filters www.bandcexpress.co.uk