JustBendIt
Grey Hound
Having been involved in the motor trade for 20 years and specifically the performance exhaust market for 10 years I can tell you the following
1. "performance pipes" on bikes, especially single cylinders, make very little to no measurable power improvement. All they do is shift the power curve, usually higher up in the rpm range - the bike feels stronger when ridden harder but has in fact lost power and torque lower down in the rpm range. These pipes usually negatively affect (increase) the fuel consumption because they usually get ridden harder with the performance pipe - bigger throttle openings = more fuel used = simple. To create power and torque in an exhaust you need to be able to play with length - on a bike you have very little or no room to add length - especially in the header pipes - as opposed to exhaust systems on cars.
On my 1999 Porsche 911 Carrera 4 (3,4 litre water cooled flat 6 engine) I have built an exhaust system that has more length, has 6 silencers and 4 harmonic chambers (to reduce drone) - it is quieter in volume than the OEM exhaust but has a lekker deep tone (different to volume). I reduced the pipe diameter from the original 54 mm OD to 50 mm OD. The car gained 6 kW at the top (2,7% over std which you really cannot feel via the "bum dyno") but has also gained 28 Nm of torque lower down (extra 8%) - this is what I was after and it feels great. I did remove the 2 cats purely because they were so big and heavy and generated a lot of heat soak. This car only has lambda sensors before the cats so its "brain" / ECU does not know that the cats have been removed and thus no reprogramming is required to make it safe but I do have plans to Unichip the car and fine tune the fuelling and timing to fully exploit the new exhaust system.
Owners / riders think they are going faster or bike is stronger because it makes more noise so they ride after the noise. Sound and performance have nothing in common - the extra sound comes from the more freeflow design of the performance pipe and the fact that it is made of lighter and thinner materials that absorb less sound and has less glass fibre packing inside.
2. On a lot of modern fuel injected motors (bikes and cars) removing the catalytic converter will again negatively affect the fuel consumption and cause a loss in power and torque lower down in the rpm range.
This is again because there is a reduction in back pressure and the exhaust is not properly scavenging spent gases but is relying more on the motor to push the gases through the exhaust system. The exhaust system actually has a vacuum / scavenging effect - it sucks gases from the combustion chamber via the engine pulsing - as well as the engine itself pushing the gases out - this is why back pressure is so important to fully utilise the scavenging effect of the pulses.
Modern catalytic converters (last 10 years) are very efficient and offer very little resistance / restriction compared to the first cats that came out in this country in the early 90s - removing cats today really has little or no effect - especially on small engines.
I replaced the original dual silencers and cat on my 650 Dakar many years ago with a freeflow silencer - the results were disgusting. The noise was unbearable and the fuel consumption went from 4 l / 100 km to 10 l / 100 km. The bike lost all torque and power at the bottom and middle of the rpm range and could not exceed 150 kph as opposed to the 195 kph I would regularly see on the clock with the OEM exhaust system.
3. It is a myth that by removing the cat you will be able to safely run leaded fuel.
All FI engines will have an oxygen / lambda sensor in the exhaust system, usually two (one before and one after the cat) - these sensors measure stoichiometric fuel : air mixture via resistance and heat (the hotter the sensor gets the more the resistance (in ohms) gets - i.e. the mixture is leaning out from the ideal 13:1 ratio - more air less fuel pushes the temps up and vice versa and the sensor relays these signals back to the ECU which can adjust fuelling and timing to bring the mixture back in line.
The lambda sensors will quickly get fouled and contaminated by the lead in the leaded fuel and stop working or give incorrect readings causing the ECU to adjust fuelling incorrectly or go into limp mode = retard ignition timing and richen fuel mixture to such an extent to make the bike "safe" to be ridden and not risk melting / cracking internals due to too lean a mixture causing it to run too hot.
The cats do get fouled by leaded fuel (that is true) but not before the lambda sensors are contaminated - so what usually happens is either the engine runs too lean = excessive combustion temps = cat actually melts together / cracks up and blocks the exhaust OR the ECU richens the mixture to such an extent that the cat gets blocked up by "sooty unburnt fuel" in the exhaust gases.
The actual combustion chamber can take the leaded fuel but the emissions system does not like it.
4. The benefit of performance pipes is usually a substantial weight reduction and less heat soak = great on bikes.
On my carb fed 950SE the Akropovic pipes must weigh less than half of the OEM pipes (I have not actually weighed them so can't give you a scientific mass measurement but I know its substantial) - this is purely because the OEM canisters are made from super heavy super thick stainless steel with substantial baffling inside (and have small lightweight cats in = negligible weight) nd are also bigger in diameter than the Akros - but they are much quieter. This is because all that extra material absorbs more sound. I like this AND because I am a tappit at heart I smaak the Akros more simply because they look cooler and have a big yellow, red and black sticker on the side which must obviously make them better then the OEM exhausts.
The big disadvantage of the above OEM canisters and catalytic converters (besides weight) is the heat soak - they run so hot and retain their heat for so long that they have been known to melt the plastics in slow heavy technical riding - and I can feel the heat radiating on my legs. I don't like this. You can reduce heat soak by having your exhausts ceramic coated - I highly recommend this - it really works well and looks great too - and does not burn off / chip / crack.
Cats are usually made from a ceramic / stainless steel wire honeycomb and need to get super hot to work properly and thus greatly contribute to heat soak.
5. Loud pipes = greater fatigue on long rides.
This is purely my opinion. On a touring DS bike I like it to be as quiet as possible - this enables me to enjoy my surroundings more instead of constantly being bombarded by exhaust noise. I am certain that it reduces fatigue - especially on long long rides. It also makes bikes more acceptable to other people in remote areas = very important to me.
Hopefully I have passed the point of being young and dum and I really don't like loud pipes anymore - this is why I have retained the dB killers in my Akros - the sound is still on the "too loud" side for my liking but the beat is pleasant and the reduced weight and heat soak advantages outweigh the increased sound disadvantage.
This is an important consideration for me in a DS bike. This is also the reason why I have retained the stock exhaust system on the 525 that I will be campaigning in the Amageza this year - 12 plus hours a day riding a moving noise machine does not appeal to me and I know it will greatly increase my fatigue.
Lastly - please remember that the manufacturers spend millions on R&D on all aspects and components on the vehicles they build - this is done to meet legislation but also to enhance customer satisfaction and create a quality product that should last.
Nobody is more interested in saving money on build costs than they are (so they can make more profit) - if they could save bucks by building and supplying cheap lightweight freeflow noisy exhausts that would last as long as the OEM units and meet all the legislation and customer requirements then they would not hesitate - believe me.
1. "performance pipes" on bikes, especially single cylinders, make very little to no measurable power improvement. All they do is shift the power curve, usually higher up in the rpm range - the bike feels stronger when ridden harder but has in fact lost power and torque lower down in the rpm range. These pipes usually negatively affect (increase) the fuel consumption because they usually get ridden harder with the performance pipe - bigger throttle openings = more fuel used = simple. To create power and torque in an exhaust you need to be able to play with length - on a bike you have very little or no room to add length - especially in the header pipes - as opposed to exhaust systems on cars.
On my 1999 Porsche 911 Carrera 4 (3,4 litre water cooled flat 6 engine) I have built an exhaust system that has more length, has 6 silencers and 4 harmonic chambers (to reduce drone) - it is quieter in volume than the OEM exhaust but has a lekker deep tone (different to volume). I reduced the pipe diameter from the original 54 mm OD to 50 mm OD. The car gained 6 kW at the top (2,7% over std which you really cannot feel via the "bum dyno") but has also gained 28 Nm of torque lower down (extra 8%) - this is what I was after and it feels great. I did remove the 2 cats purely because they were so big and heavy and generated a lot of heat soak. This car only has lambda sensors before the cats so its "brain" / ECU does not know that the cats have been removed and thus no reprogramming is required to make it safe but I do have plans to Unichip the car and fine tune the fuelling and timing to fully exploit the new exhaust system.
Owners / riders think they are going faster or bike is stronger because it makes more noise so they ride after the noise. Sound and performance have nothing in common - the extra sound comes from the more freeflow design of the performance pipe and the fact that it is made of lighter and thinner materials that absorb less sound and has less glass fibre packing inside.
2. On a lot of modern fuel injected motors (bikes and cars) removing the catalytic converter will again negatively affect the fuel consumption and cause a loss in power and torque lower down in the rpm range.
This is again because there is a reduction in back pressure and the exhaust is not properly scavenging spent gases but is relying more on the motor to push the gases through the exhaust system. The exhaust system actually has a vacuum / scavenging effect - it sucks gases from the combustion chamber via the engine pulsing - as well as the engine itself pushing the gases out - this is why back pressure is so important to fully utilise the scavenging effect of the pulses.
Modern catalytic converters (last 10 years) are very efficient and offer very little resistance / restriction compared to the first cats that came out in this country in the early 90s - removing cats today really has little or no effect - especially on small engines.
I replaced the original dual silencers and cat on my 650 Dakar many years ago with a freeflow silencer - the results were disgusting. The noise was unbearable and the fuel consumption went from 4 l / 100 km to 10 l / 100 km. The bike lost all torque and power at the bottom and middle of the rpm range and could not exceed 150 kph as opposed to the 195 kph I would regularly see on the clock with the OEM exhaust system.
3. It is a myth that by removing the cat you will be able to safely run leaded fuel.
All FI engines will have an oxygen / lambda sensor in the exhaust system, usually two (one before and one after the cat) - these sensors measure stoichiometric fuel : air mixture via resistance and heat (the hotter the sensor gets the more the resistance (in ohms) gets - i.e. the mixture is leaning out from the ideal 13:1 ratio - more air less fuel pushes the temps up and vice versa and the sensor relays these signals back to the ECU which can adjust fuelling and timing to bring the mixture back in line.
The lambda sensors will quickly get fouled and contaminated by the lead in the leaded fuel and stop working or give incorrect readings causing the ECU to adjust fuelling incorrectly or go into limp mode = retard ignition timing and richen fuel mixture to such an extent to make the bike "safe" to be ridden and not risk melting / cracking internals due to too lean a mixture causing it to run too hot.
The cats do get fouled by leaded fuel (that is true) but not before the lambda sensors are contaminated - so what usually happens is either the engine runs too lean = excessive combustion temps = cat actually melts together / cracks up and blocks the exhaust OR the ECU richens the mixture to such an extent that the cat gets blocked up by "sooty unburnt fuel" in the exhaust gases.
The actual combustion chamber can take the leaded fuel but the emissions system does not like it.
4. The benefit of performance pipes is usually a substantial weight reduction and less heat soak = great on bikes.
On my carb fed 950SE the Akropovic pipes must weigh less than half of the OEM pipes (I have not actually weighed them so can't give you a scientific mass measurement but I know its substantial) - this is purely because the OEM canisters are made from super heavy super thick stainless steel with substantial baffling inside (and have small lightweight cats in = negligible weight) nd are also bigger in diameter than the Akros - but they are much quieter. This is because all that extra material absorbs more sound. I like this AND because I am a tappit at heart I smaak the Akros more simply because they look cooler and have a big yellow, red and black sticker on the side which must obviously make them better then the OEM exhausts.
The big disadvantage of the above OEM canisters and catalytic converters (besides weight) is the heat soak - they run so hot and retain their heat for so long that they have been known to melt the plastics in slow heavy technical riding - and I can feel the heat radiating on my legs. I don't like this. You can reduce heat soak by having your exhausts ceramic coated - I highly recommend this - it really works well and looks great too - and does not burn off / chip / crack.
Cats are usually made from a ceramic / stainless steel wire honeycomb and need to get super hot to work properly and thus greatly contribute to heat soak.
5. Loud pipes = greater fatigue on long rides.
This is purely my opinion. On a touring DS bike I like it to be as quiet as possible - this enables me to enjoy my surroundings more instead of constantly being bombarded by exhaust noise. I am certain that it reduces fatigue - especially on long long rides. It also makes bikes more acceptable to other people in remote areas = very important to me.
Hopefully I have passed the point of being young and dum and I really don't like loud pipes anymore - this is why I have retained the dB killers in my Akros - the sound is still on the "too loud" side for my liking but the beat is pleasant and the reduced weight and heat soak advantages outweigh the increased sound disadvantage.
This is an important consideration for me in a DS bike. This is also the reason why I have retained the stock exhaust system on the 525 that I will be campaigning in the Amageza this year - 12 plus hours a day riding a moving noise machine does not appeal to me and I know it will greatly increase my fatigue.
Lastly - please remember that the manufacturers spend millions on R&D on all aspects and components on the vehicles they build - this is done to meet legislation but also to enhance customer satisfaction and create a quality product that should last.
Nobody is more interested in saving money on build costs than they are (so they can make more profit) - if they could save bucks by building and supplying cheap lightweight freeflow noisy exhausts that would last as long as the OEM units and meet all the legislation and customer requirements then they would not hesitate - believe me.
