Five steps for Performance Perfection

Stock motorcycles are compromised by noise and emissions regulations, budgets and the need to accommodate a vast range of riders and conditions. We explore the top five ways to iron out the production creases to give you a crisper, sharper machine

POWER COMMANDER

It's expensive but it will add power and improve throttle response. Or will it? And does your bike need it? Here's the low-down on that little black box

Average cost £298 for Power Commander, from £150 for a custom map

Contact: Dynojet UK, (01995) 600500

Most modern bikes come with electronic fuel injection (EFI). It works like this: an on-board computer (the electronic control unit, or ECU) gathers information from a number of sensors that detect factors such as throttle position, crank and cam position, air temperature, engine temperature, intake air pressure and atmospheric pressure. The ECU then refers to a table of pre-programmed injector settings in its memory (the 'map') and sends a signal to the bank of injectors telling them exactly how much fuel to deliver to the throttle bodies, where it mixes with air before entering the cylinder. The fuel/air mixture determines how well the engine runs. A rich mixture (too much fuel) means unburned fuel will go to waste in the exhaust gases, while a lean mixture (too little) means the engine will run hot, lose power and possibly melt and wear engine internals (fuel helps cool valves, cylinders and pistons). For complete combustion the fuel/air ratio must be around 14.7:1 - that's 14.7lb of air to a pound of petrol. But complete isn't always best. Optimum combustion produces maximum power and is achieved with a slightly rich mixture (up to 10% air deficiency), while a slightly lean mixture (up to 10% air surplus) will give the best economy. The optimum fuel ratio sits between 12.8:1 and 13.2:1, but manufacturers have parameters to account for.

A standard fuel map must operate within legal emissions limits. And because a rich mixture flattens the exhaust note, some bikes run rich where the noise test is carried out. This means many injected bikes will have a rich mixture-induced glitch at around 5500rpm. Original maps also allow for differences in manufacturing tolerances, so the fuelling has to work both on a worst and best-case standard engine. They must also take into account engine life (which extra power and cylinder pressures might reduce) and the poorest quality fuel likely to be used.

Dynojet's Power Commander is a plug-in device that overrides the original map either to compensate for changes to the bike or just improve on the standard map - there's usually scope for doing so even without making any other changes, given the regulations manufacturers are forced to comply with.

Creating a new fuel map is a painstaking exercise that involves sticking the bike on a dyno and working through the rev range incrementally by rpm and throttle opening, adjusting the fuelling first at standard atmospheric temperature and pressure (STP). Algorithms (think back to those large books of numbers from school that translated into flow charts and computer programmes) also have to be utilised to alter the fuelling when the engine is accelerating rather than being held at constant rpm, deal with that stutter problem from closed throttle to open, and soften the power delivery as you open the throttle to make the bike more controllable.

A properly-fuelled bike can be a joy to ride and a night-and-day transformation compared to the standard set-up, but bear in mind that the improvements to a remapped engine may not be to everyone's tastes. The more precise fuelling and instant throttle response of a well set-up Power Commander can be in marked contrast to the relatively woolly response that comes as standard. Ideally remapping should be done on a dyno, by a trained operator and on an individual bike basis, but downloadable maps for specific bike and exhaust combinations are available on the internet.

POWER COMMANDER VERDICT

Results depend on a bike's standard set-up. Improvements can be dramatic or barely noticeable, so stick your bike on a dyno or get a feel for glitches before spending your hard-earned.

COST 1/5

EFFECTIVENESS 4/5

OVERALL 3/5

EXHAUST SYSTEMS

Probably the most common mod out there, exhausts will boost your street cred. But how about performance?

Average cost £60-£500 end can, £800-£1500 full system

Srandard exhausts come under the noise and emissions microscope. They route poisonous gases from the combustion chamber to the outside world, and must do it in the least offensive way possible. So they're restricted - although the bulk of the restriction is in the end can with headers and downpipes focused on influencing power characteristics.

The exhaust system must scavenge gases as efficiently as possible to make way for optimum intake. The better the gas flows through the system, the larger the quantity of gas the exhaust will be able to scavenge, the greater the vacuum in the combustion chamber will be and the stronger the next intake.

Pressure waves play a big part in optimising gas flow. The sound of the exhaust gas expelled from the exhaust valve forms a high-pressure wave that travels down the pipe. As it reaches the open end, it's reflected back up the pipe as a low pressure wave. If the low-pressure wave arrives at the exhaust valve just as it's opening again it helps to scavenge the next charge of gas, improving the engine's efficiency. As low pressure waves travel back up the pipe they're inverted once more into high pressure waves. If these reach the exhaust valve just as it's closing they can force any fresh inlet charge that might be escaping past it back into the cylinder, which also improves engine efficiency.

The length of the header pipes determine where the pressure waves are, and they need to take account of engine speed. A low pressure pulse that can reach an exhaust valve at 4000rpm might only be half way towards it at 8000rpm, so you end up with low pressure waves arriving at exhaust valves when you need high pressure ones. Other factors come into play: a larger pipe bore will flow more gas and boost top-end, while a smaller bore sucks burnt gas from the cylinder faster to boost low-end power. Tapering the pipes also speeds up flow. Formation affects characteristics too: a 4-1 system will boost top-end while a 4-2-1 broadens the powerband.

Ultimately, exhausts are designed for optimum power at either low or high revs. Some manufacturers fit electronically-controlled valves in their exhausts, such as Yamaha's EXUP or Suzuki's SAEC, to control the flow of pressure waves at lower rpm without sacrificing so much higher up. They are usually lost with an aftermarket full system, but as they only do their work up to 4000rpm or so, losing them won't sacrifice as much driveability as you might think. Race systems work under the assumption that you want to sacrifice driveability for maximum power, so while it could add up to 15bhp up top the bike could end up feeling flat at anything below 8000rpm. Meanwhile, the standard downpipes deliver useable rather than ultimate power.

If the exhaust system is improved without a fuelling remap, the engine may be unable to draw in more fuel - but it will draw in more air, diluting the mixture. However, clever design, taking advantage of a bike's rich standard fuelling set-up optimised to meet emissions regulations, means some full systems work well on standard bikes without fuelling mods.

Changing the end can is a more popular and less radical mod. A standard silencer routes the noisy gases back and forth through a series of energy sapping chambers before releasing them quietly. By not complying with noise levels an aftermarket can will flow the gases more directly, reducing the average gas pressure (back pressure) in the system so the gases escape more easily. Results vary depending on a bike's standard set-up, but the engine should make more power even without a remap (as long as the can is well designed). An end can alone is usually not enough to make an engine run dangerously lean.

EXHAUST VERDICT

A full race system will get you more power but at the expense of driveability, while an aftermarket end can will release less power but without drastic effects on the powerband - or the absolute need for a remap. Our end can test last year showed an average gain of 2bhp, a maximum gain of 5bhp and a loss of 1bhp in one cheap case.

COST 3/5

EFFECTIVENESS 4/5

OVERALL 4/5

GEARING

Substantial acceleration performance for next to no money? So where's the catch?

Average cost £12

Contact B&C Express, (01522) 791369

The six gears in your bike's gearbox are designed to make best use of the engine and, as with most things, they battle with compromise. The gear ratio must produce the right rpm for decent fuel consumption and smooth running in top, with enough left for good acceleration. Production bikes are also frequently overgeared to pass drive-by noise regulations, and if manufacturers gear them too low there could be liability issues with monkeys looping them. There are big benefits in optimising the gearing for your individual purpose, and on most bikes, gearing down means unleashing substantial acceleration performance that you'll make use of at every corner exit, at the expense of very high top speed that you'll probably never use.

While most of us won't be able to change the ratios in the gearbox, we can play with the final drive ratio, aka the front and rear sprockets. The final drive transmits torque from the gearbox to the rear wheel and the final drive ratio is the number of turns the gearbox makes to each single turn of the rear wheel. Finding it is easy: just divide the driven gear by the drive gear - in the case of a Honda CBR600RR with a 42T rear sprocket and a 16T front, the ratio will be 42/16, which equals 2.6. So 2.6:1 is the ratio of turns the gearbox sprocket makes to turn the rear wheel one revolution.

Fitting a bigger rear sprocket or a smaller front will reduce the final drive ratio, lowering the gearing. This increases the number of turns the gearbox sprocket makes to each single turn of the rear wheel, lowering the speed the bike will achieve in each gear but giving it harder acceleration (it 'shortens' each gear). Instead, fitting a smaller rear or a bigger front sprocket raises the final drive ratio and the resulting taller gearing increases the speed the bike will achieve in each gear at the expense of acceleration.

Knocking a tooth off the front sprocket is equivalent to adding three on the rear; it's a simpler mod as you won't need to fit a chain with extra links, but bear in mind a 14T front sprocket is the absolute minimum a chain can wrap itself around without severe wear.

However, there are downsides to changing the gearing. The accuracy of your bike's gearbox-driven speedo could be affected, and because the engine will rev higher it could become uncomfortable to cruise at certain speeds. Fuel consumption can also go up, which could prove expensive in the long run. So experiment with small alterations at a time rather than going for big changes, and treat every motorcycle individually. Get a feel for your bike: if it revs forever in each gear you can gear down substantially, but if you're hitting the limiter too quickly gear up for more speed in each gear. The best thing with gearing is that if you do get it wrong, it'll barely dent your bank statement and you can return it to standard in no time.

GEARING VERDICT

Little more than a tenner and an hour of your time will unleash performance gains that would otherwise cost a pretty penny in tuning and take up days on the dyno. But beware the downsides of going too radical.

COST 5/5

OVERALL 4/5

SUSPENSION

Whether you simply use your suspension's adjustment range or go for a complete overhaul, it'll be worth it

Set-up £40, Rrevalve & respring front £375, rear from £300,contact Shockwave (01530) 563238, K-Tech (01530) 810625

Good quality suspension keeps a motorcycle composed as you accelerate, brake and ride over dodgy surfaces, letting you use power, brakes, tyres and handling to their full potential. But while top flight race bikes are set up so exactly for particular rider/tyre/ weather combinations that they feel horrible should any of these shift, production bikes work well whether you're a nine-stone waif on a potholed road surface or a 20-stone porker on a track day. Which is no bad thing as you will probably be riding your bike in all kinds of conditions. But production components are always built down to a price and the compromise in accommodating so many variables means there's plenty of scope for improvement.

The first route to explore is adjusting the standard components. A shock or fork leg's spring is controlled by oil that moves at a rate determined by a piston and shims inside the body. Production stuff is generally adjustable for preload and compression and rebound damping. Preload is the amount of tension set in a spring before a load (rider/braking force) is applied. Without it your bike would sag massively under the weight of the bike alone; too much and the suspension would hardly move. Rebound damping controls the speed your springs bounce back after being compressed, while compression damping controls the speed the springs compress under load. If you're fiddling, write down the standard settings first so that if the set-up goes tits-up you can revert back to stock. Check out the May 2003 issue of TWO for a special on how to adjust your suspension.If you're serious about suspension, a revalve and respring will overhaul your standard components without the expense of replacing them. After fitting a spring to suit your weight the damping needs sorting to match the new spring rate. A revalve usually involves changing the compression piston, shims and rod, with the adjusters acquiring a better range.

If you are going to splash out on aftermaket components, consider having them tailor built rather than buying off-the-shelf. Top-end kit will be precisely engineered from lightweight materials (magnesium and aluminium instead of steel) and will be adjustable for high- and low-speed damping (the speed at which the spring compresses and rebounds over a bump, not the speed of the motorcycle!). If your standard shock is not adjustable for ride height you can get one that is, and you can replace right way up forks with upside down ones - although this is more of a fashion statement that will require different yokes to accommodate the stanchions' wider diameter. The most common practice is to replace the rear shock and change the fork internals, as there is only one shock versus two very expensive fork legs.

SUSPENSION VERDICT

Improving your bike's suspension is probably the most effective upgrade you could make to your machine.

COST 3/5

EFFECTIVENESS 5/5

OVERALL 4/5

TYRES

Those little black rubber numbers that make it all possible. But which should you go for?

Average cost £250 a set

Production motorcycles come fitted with the latest road tyres to suit the bike's intended purpose. Tyres are expensive, which means you don't want to be changing them needlessly, so unless you're converting your machine into a track bike you might as well wear them out first. But when the time comes for a change, think carefully about what to go for; don't go for the 'stickiest' race compound just because your mate who raced reckons they're the best for the job.

Each tyre is tailored for its specific purpose. A track tyre may have the softest - hence grippiest - compound, but tyres only work when they reach their optimum temperature. A track tyre is chemically designed to operate at constant, high temperatures reached by the extreme pace of track riding, and is rarely achieved on the road. And because it is designed to live at high temperatures the race compound will also take longer to reach its peak. Use these tyres on the road and no matter how fast you ride you'll be forced to slow for traffic and Gatsos, and every time you stop the tyres will cool off and take ages to warm up again. Not only will grip suffer, but the tyres will wear quickly, shred with cold tearing and, because they're not as resistant to heat cycles, the compound will deteriorate fast. Instead, a sporty road tyre will warm up quickly and maintain its temperature, and the Silica in its compound will ensure grip in cold and damp conditions too. This leaves you with loads of grip and longevity - no contest, really.Racing slicks have a radical profile and flexible sidewall designed to work on highly tuned race chassis, so don't be tempted to try them on a track day. If you really want slicks try Michelin's Track Day Slicks that have a road profile to suit road bikes. However, the road legal Metzeler RaceTecs or Michelin Pilot Power Race are grippy as hell on a dry track (where they belong), with a sharper profile for quicker turn-in compared to the rounder, more stable road tyre. A sporty road and track tyre like Pirelli's Diablo Corsa will provide you with ideal performance in most road and track situations. If you ride purely on the road and want longevity, then road tyres such as Metzeler Sportecs are perfect. Incorrect tyre pressures and worn or squared-off tyres will affect handling, so check with the manufacturer what pressures to run and replace them before they reach advanced levels of baldness - it's cheaper to replace tyres than bikes.

TYRE VERDICT

The right tyre for the job makes all the difference, so be honest with yourself about the tyres you need.

COST> 2/5

EFFECTIVENESS 5/5

OVERALL 4/5

THE END OF THE ROAD

All production bikes are compromised by budgets, broad usage parameters, and noise and emissions regulations, so there is always scope to improve on what will be an excellent package. But learn about your motorcycle first before splashing out on the popular performance mods; find out its weak points as no two bikes are the same, and when you do make the change, make sure it suits you and your riding. Get it wrong and at best you could throw away substantial beer money, at worst you could ruin your bike's performance (and throw away beer money). Get it right and you could be rewarded with the closest you'll get to perfection on two wheels.


POWER COMMANDER

It's expensive but it will add power and improve throttle response. Or will it? And does your bike need it? Here's the low-down on that little black box

Most modern bikes come with electronic fuel injection (EFI). It works like this: an on-board computer (the electronic control unit, or ECU) gathers information from a number of sensors that detect factors such as throttle position, crank and cam position, air temperature, engine temperature, intake air pressure and atmospheric pressure. The ECU then refers to a table of pre-programmed injector settings in its memory (the 'map') and sends a signal to the bank of injectors telling them exactly how much fuel to deliver to the throttle bodies, where it mixes with air before entering the cylinder. The fuel/air mixture determines how well the engine runs. A rich mixture (too much fuel) means unburned fuel will go to waste in the exhaust gases, while a lean mixture (too little) means the engine will run hot, lose power and possibly melt and wear engine internals (fuel helps cool valves, cylinders and pistons). For complete combustion the fuel/air ratio must be around 14.7:1 - that's 14.7lb of air to a pound of petrol. But complete isn't always best. Optimum combustion produces maximum power and is achieved with a slightly rich mixture (up to 10% air deficiency), while a slightly lean mixture (up to 10% air surplus) will give the best economy. The optimum fuel ratio sits between 12.8:1 and 13.2:1, but manufacturers have parameters to account for.

A standard fuel map must operate within legal emissions limits. And because a rich mixture flattens the exhaust note, some bikes run rich where the noise test is carried out. This means many injected bikes will have a rich mixture-induced glitch at around 5500rpm. Original maps also allow for differences in manufacturing tolerances, so the fuelling has to work both on a worst and best-case standard engine. They must also take into account engine life (which extra power and cylinder pressures might reduce) and the poorest quality fuel likely to be used.

Dynojet's Power Commander is a plug-in device that overrides the original map either to compensate for changes to the bike or just improve on the standard map - there's usually scope for doing so even without making any other changes, given the regulations manufacturers are forced to comply with.

Creating a new fuel map is a painstaking exercise that involves sticking the bike on a dyno and working through the rev range incrementally by rpm and throttle opening, adjusting the fuelling first at standard atmospheric temperature and pressure (STP). Algorithms (think back to those large books of numbers from school that translated into flow charts and computer programmes) also have to be utilised to alter the fuelling when the engine is accelerating rather than being held at constant rpm, deal with that stutter problem from closed throttle to open, and soften the power delivery as you open the throttle to make the bike more controllable.

A properly-fuelled bike can be a joy to ride and a night-and-day transformation compared to the standard set-up, but bear in mind that the improvements to a remapped engine may not be to everyone's tastes. The more precise fuelling and instant throttle response of a well set-up Power Commander can be in marked contrast to the relatively woolly response that comes as standard. Ideally remapping should be done on a dyno, by a trained operator and on an individual bike basis, but downloadable maps for specific bike and exhaust combinations are available on the internet.

POWER COMMANDER VERDICT
Results depend on a bike's standard set-up. Improvements can be dramatic or barely noticeable, so stick your bike on a dyno or get a feel for glitches before spending your hard-earned.

COST 1/5
EFFECTIVENESS 4/5
OVERALL 3/'5

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