I'm thinking of fitting a non-standard exhaust for several reasons mainly-
It's extremely quite as is, drivers struggle to hear me and it cannot be heard over the other other bike at school, an r125,
It sounds like a moped at high rpm's
Curent exhaust is rusting,
But I cannot afford the 'package' aftermarket systems so I was thinking of doing 1 of three things, 1-leave it, 2- buy a link pipe and a aftermarket can, 3- get the local blacksmiths to bend a bit of pipe for the link pipe the buy an aftermarket can.
However my Vara is an '05, so it's carbureted. The current carbs are set up for the original exhaust so will messing with the link pipe and can mess with all the Honda engineers work and have catastrophic effect on the running of the engine and on my fuel economy, or will it run ok?
See the other thread Here (http://www.honda-varadero-uk.org/forum/index.php?topic=10230.0)
I have the injection version, so the ECU takes care of the fuelling, but as far as I know, you won't have to fiddle with the carbs too much - because of the restrictions already in place in the downpipes.
Quote from: Taught2BeCautious on 03/10/14 - 15:38:46
See the other thread Here (http://www.honda-varadero-uk.org/forum/index.php?topic=10230.0)
I have the injection version, so the ECU takes care of the fuelling, but as far as I know, you won't have to fiddle with the carbs too much - because of the restrictions already in place in the downpipes.
Thanks for your reply.
So it would involve carb adjustment then? To what extent?
I don't know how much you know about fuel flow through an engine so I will go through the basics. I am not trying to be patronising, just educational.
Air plus fuel metered by the carbs flows into the cylinder through the inlet valve(s) by reduced pressure as the piston travels down the barrel. It produces an explosive mixture ignited by the spark plug which pushes the piston down creating power. The spent fuel exits the barrel through the exhaust valve and then the pipework of the exhaust.
All this is calculated by the manufacturer to ensure enough, but not too much fuel enters the engine. The engine runs at the correct temperature to produce maximum power and burns all the fuel cleanly and the exhaust flow empties the spent gases just in time for the next cycle.
Tampering with either side of this equation can lead to problems.
Too little fuel entering can lead to pre detonation as it is not "wet" enough to prevent premature detonation. The piston travelling up the bore is met with an explosion too soon.
Too much fuel leaves unburnt fuel in the exhaust cycle leading to popping and banging as fuel burns in the exhaust system.
Having the burnt charge (exhaust gases) flow out of the cylinder too quickly leads to increase in vacuum pre inlet phase. This thins the air fuel ratio as the carb delivers finely metered fuel through a tiny hole in the main jet whilst the air is sucked in, in big gulps, through the body of the carb.
So if you unbalance this situation you need to be able to correct it.
If you increase the gas flow on the exhaust side by fitting a freer flowing exhaust you have to pump more fuel in. This will involve fitting bigger main jets to the carb and possibly raising the needle of the slide. There are two ways to check and adjust. Buy a colourtune and watch the spark explosion, adjusting air/fuel mixture on what you see. Or pay someone to set it up on a Dynometer. About ?140. Or leave well alone.
Increasing the carb fuel flow just wastes money, pollutes the oil with unburnt petrol and stinks if you are following this bike!.
If any of the above seem unfamiliar to you should you really be messing with it?
Live with the limitations of what is a small capacity bike built by the biggest manufacturer in the world.
you mention a noisy R125. Is it any quicker?
Don't mean to put a downer on your biking experience but as a lad I didn't know any better and blew several engines, two stroke and four stroke, up. In my youth they were ?25 to ?50 a time. Can you afford to kiss goodbye to your current investment in motorcycling
All the best
The Prodded Dog
@ TPD sage words and advice.
JK
Quote from: The Prodded Dog on 04/10/14 - 20:53:10
I don't know how much you know about fuel flow through an engine so I will go through the basics. I am not trying to be patronising, just educational.
Air plus fuel metered by the carbs flows into the cylinder through the inlet valve(s) by reduced pressure as the piston travels down the barrel. It produces an explosive mixture ignited by the spark plug which pushes the piston down creating power. The spent fuel exits the barrel through the exhaust valve and then the pipework of the exhaust.
All this is calculated by the manufacturer to ensure enough, but not too much fuel enters the engine. The engine runs at the correct temperature to produce maximum power and burns all the fuel cleanly and the exhaust flow empties the spent gases just in time for the next cycle.
Tampering with either side of this equation can lead to problems.
Too little fuel entering can lead to pre detonation as it is not "wet" enough to prevent premature detonation. The piston travelling up the bore is met with an explosion too soon.
Too much fuel leaves unburnt fuel in the exhaust cycle leading to popping and banging as fuel burns in the exhaust system.
Having the burnt charge (exhaust gases) flow out of the cylinder too quickly leads to increase in vacuum pre inlet phase. This thins the air fuel ratio as the carb delivers finely metered fuel through a tiny hole in the main jet whilst the air is sucked in, in big gulps, through the body of the carb.
So if you unbalance this situation you need to be able to correct it.
If you increase the gas flow on the exhaust side by fitting a freer flowing exhaust you have to pump more fuel in. This will involve fitting bigger main jets to the carb and possibly raising the needle of the slide. There are two ways to check and adjust. Buy a colourtune and watch the spark explosion, adjusting air/fuel mixture on what you see. Or pay someone to set it up on a Dynometer. About ?140. Or leave well alone.
Increasing the carb fuel flow just wastes money, pollutes the oil with unburnt petrol and stinks if you are following this bike!.
If any of the above seem unfamiliar to you should you really be messing with it?
Live with the limitations of what is a small capacity bike built by the biggest manufacturer in the world.
you mention a noisy R125. Is it any quicker?
Don't mean to put a downer on your biking experience but as a lad I didn't know any better and blew several engines, two stroke and four stroke, up. In my youth they were ?25 to ?50 a time. Can you afford to kiss goodbye to your current investment in motorcycling
All the best
The Prodded Dog
Many thanks for your detailed reply, I knew the basics of carbs in theory so no harm done in going over it :) The r125 is actually on its stock exhaust but is significantly quicker than the vara (put that down to the more torque, less weight and 15000 mile younger engine). I really don't want to ruin my fuel economy (or my engine for that matter), but nor do I want to be hit by an unobservant driver. Is there no truth in @Taught2BeCautious 's statement saying that the pressure restrictions are done by the downpipes and not the end silencer?
Thanks
@BabyVararider. If you find yourself i a situation where you think that making a noise will save you from inattentive drivers, blow the horn.
JK
I agree with TPD, but consider the following:
As the piston travels down the cylinder on the intake stroke, the inlet valve opens, and air/fuel mixture is drawn into the cylinder.
Just before the piston reaches the bottom of it's stroke, the inlet valve closes.
The piston rises on the compression stroke, and just before it reaches the top, a spark ignites the mixture.
The expanding gasses force the piston back down the cylinder again on the power stroke. The amount of power generated is proportional to the amount of fuel/air that was burned. Just before the piston reaches the bottom of the cylinder, the exhaust valve starts to open and the burned gasses start to make their way into the exhaust system under pressure.
Momentum stored in the flywheel causes the piston to rise again, expelling the remainder of the gases through the open exhaust valve.
Just before the piston reaches the top of the exhaust stroke, the burned gasses that are already in the exhaust system have started to cool and contract, which together with the momentum they have generated, help to expelled the remaining burned gasses from the cylinder, and then the exhaust valve closes tight ready for the whole process to start again.
That's a pretty simple explanation of the 4 stroke or 'Otto' cycle.
Now imagine its 1999 and you are the development engineer at Honda, and you have the very first engine off the production line ready for testing. You lash it up to the dynomometer and the damn thing is putting out 18 or more bhp!
The boss is going to fire you unless you can come up with a way of getting the output down to 14.6bhp - or they won't be able to sell the bike in the European learner market - and who is going to buy an 18bhp 125 after passing their test?
What do you do?
You could completely re-engineer the cylinder head with smaller valves and re-engineer the camshaft to alter the valve timing and dwell angles - but that is going to cost a lot of time and money in re-tooling the production line.
An easy fix would be to reduce the size of the air filter and put a restrictor bung in the airbox. This is cheap, easy and quick, because the air filter is made by an external contractor. This works by reducing the airflow, so there's less air flowing through the carburettors and it does make a difference to the output - but we're still not down to 14.6bhp.
Next thing to try, is to put a restrictor in the exhaust headers, which is also a cheap, easy and quick fix because they are made by another external contractor.
This works because it creates a small amount of back-pressure in the exhaust system, so when the exhaust valve shuts, not all of the burned gasses have escaped from the cylinder - and when the inlet valve opens and the piston travels down the cylinder, it won't be able to draw in as much fuel/air mixture, because some of the space is occupied by burned gasses from the previous cycle.
A smaller jet in the rear carb for good measure, and bingo - we're down to 14.6bhp.
I found the above explanation on another forum back in 2008 when I had just bought mine and was searching for information about de-restricting it. Someone had asked the same question and lots of people replied to say there weren't any restrictions - then this guy chips in, saying that he was part of the R&D team working on the 125 V-Twin engine at Honda in 1998-99.
He also said that those things were done purely to reduce the power output, although the 'official' reason was due to overheating problems caused by reduced air-flow at the rear cylinder. This makes no sense to me, because to start with, it's a water-cooled engine, and then the front cylinder is mostly covered by the front fairing, whilst air is directed towards the exposed rear cylinder by the rider's legs!
They wouldn't have gotten away with simply using restrictor plates between the carbs and the cylinders, as it would be too easily undone to get type approval in the UK.
I've not since been able to find the original post, but I do think the explanation makes more sense than anything else I have read on the subject.
I also believe the guy genuinely worked at Honda R&D, as he was the first person to mention the restrictor section welded inside the front exhaust downpipe - nobody else had noticed that!
Quote from: Taught2BeCautious on 05/10/14 - 17:12:15
I agree with TPD, but consider the following:
As the piston travels down the cylinder on the intake stroke, the inlet valve opens, and air/fuel mixture is drawn into the cylinder.
Just before the piston reaches the bottom of it's stroke, the inlet valve closes.
The piston rises on the compression stroke, and just before it reaches the top, a spark ignites the mixture.
The expanding gasses force the piston back down the cylinder again on the power stroke. The amount of power generated is proportional to the amount of fuel/air that was burned. Just before the piston reaches the bottom of the cylinder, the exhaust valve starts to open and the burned gasses start to make their way into the exhaust system under pressure.
Momentum stored in the flywheel causes the piston to rise again, expelling the remainder of the gases through the open exhaust valve.
Just before the piston reaches the top of the exhaust stroke, the burned gasses that are already in the exhaust system have started to cool and contract, which together with the momentum they have generated, help to expelled the remaining burned gasses from the cylinder, and then the exhaust valve closes tight ready for the whole process to start again.
That's a pretty simple explanation of the 4 stroke or 'Otto' cycle.
Now imagine its 1999 and you are the development engineer at Honda, and you have the very first engine off the production line ready for testing. You lash it up to the dynomometer and the damn thing is putting out 18 or more bhp!
The boss is going to fire you unless you can come up with a way of getting the output down to 14.6bhp - or they won't be able to sell the bike in the European learner market - and who is going to buy an 18bhp 125 after passing their test?
What do you do?
You could completely re-engineer the cylinder head with smaller valves and re-engineer the camshaft to alter the valve timing and dwell angles - but that is going to cost a lot of time and money in re-tooling the production line.
An easy fix would be to reduce the size of the air filter and put a restrictor bung in the airbox. This is cheap, easy and quick, because the air filter is made by an external contractor. This works by reducing the airflow, so there's less air flowing through the carburettors and it does make a difference to the output - but we're still not down to 14.6bhp.
Next thing to try, is to put a restrictor in the exhaust headers, which is also a cheap, easy and quick fix because they are made by another external contractor.
This works because it creates a small amount of back-pressure in the exhaust system, so when the exhaust valve shuts, not all of the burned gasses have escaped from the cylinder - and when the inlet valve opens and the piston travels down the cylinder, it won't be able to draw in as much fuel/air mixture, because some of the space is occupied by burned gasses from the previous cycle.
A smaller jet in the rear carb for good measure, and bingo - we're down to 14.6bhp.
I found the above explanation on another forum back in 2008 when I had just bought mine and was searching for information about de-restricting it. Someone had asked the same question and lots of people replied to say there weren't any restrictions - then this guy chips in, saying that he was part of the R&D team working on the 125 V-Twin engine at Honda in 1998-99.
He also said that those things were done purely to reduce the power output, although the 'official' reason was due to overheating problems caused by reduced air-flow at the rear cylinder. This makes no sense to me, because to start with, it's a water-cooled engine, and then the front cylinder is mostly covered by the front fairing, whilst air is directed towards the exposed rear cylinder by the rider's legs!
They wouldn't have gotten away with simply using restrictor plates between the carbs and the cylinders, as it would be too easily undone to get type approval in the UK.
I've not since been able to find the original post, but I do think the explanation makes more sense than anything else I have read on the subject.
I also believe the guy genuinely worked at Honda R&D, as he was the first person to mention the restrictor section welded inside the front exhaust downpipe - nobody else had noticed that!
An interesting story indeed, thank you. It's led me to another question, forgive me I'm new to all this. How do the aftermarket exhaust "packages" comprising of a link pipe and can, such as the scorpion system, increase the noise level without pulling more air through the system therefore warranting re-jetting and how do they then increase the power output to a level that would be illegal?
In simple terms the exhaust on a 4 stroke is mainly there to reduce the sound of the engine explosions. The bore of the header pipes and can affect the speed of spent gases exiting the system.
An aftermarket can has less internal pipework and baffling material so it is louder than stock. That is all.
It may flow better than stock so bonus HP increases though minimal, are often quoted. you are just getting a cleaner burn.
The only way to get big power increases are to stuff more fuel/air in hence turbo or super chargers to extract more power.
Manufacturers have to submit each model to meet type approval and always err on the side of caution when silencing engines. That is the operative word here, silencing. It is quite possible to run a four stroke engine on open pipes, i.e. no silencing at all, if you get the fuelling right. However environmental issues require less than 80 ish decibels at ground level.
Ever wondered why you can hear small private aircraft when they at 10,000 feet??? Yes they are running open pipes.
Here's a clip of a six cylinder 50 cc honda racer on open pipes. Is this the effect you are trying to achieve?
https://www.youtube.com/watch?v=o57JwibqCb8
For us oldies happy memories.
The Prodded Dog
Quote from: The Prodded Dog on 05/10/14 - 20:08:04
In simple terms the exhaust on a 4 stroke is mainly there to reduce the sound of the engine explosions. The bore of the header pipes and can affect the speed of spent gases exiting the system.
An aftermarket can has less internal pipework and baffling material so it is louder than stock. That is all.
It may flow better than stock so bonus HP increases though minimal, are often quoted. you are just getting a cleaner burn.
The only way to get big power increases are to stuff more fuel/air in hence turbo or super chargers to extract more power.
Manufacturers have to submit each model to meet type approval and always err on the side of caution when silencing engines. That is the operative word here, silencing. It is quite possible to run a four stroke engine on open pipes, i.e. no silencing at all, if you get the fuelling right. However environmental issues require less than 80 ish decibels at ground level.
Ever wondered why you can hear small private aircraft when they at 10,000 feet??? Yes they are running open pipes.
Here's a clip of a six cylinder 50 cc honda racer on open pipes. Is this the effect you are trying to achieve?
https://www.youtube.com/watch?v=o57JwibqCb8
For us oldies happy memories.
The Prodded Dog
That (2)50 sounds darn incredible, reminiscent of the old v12 f1 cars in some ways. But it still leaves the question of if the branded silencers and link pipes don't require fuelling adjustments why would a more custom approach (which does still have bafflling)?
There is no direct relationship between noise and power.
The main way that the Vara's exhaust system affects the power output, is that the restrictions in the downpipes (everything from the cylinder heads to the start of the link pipe) cause some of the burned gasses to remain in the combustion chamber, thereby reducing the amount of fresh fuel/air mixture available for the next power stroke.
Less fuel/air = less power. The carburettors are configured to take care of the ratio of fuel and air depending on the amount of air flowing through them.
If you think about it, the 'explosions' happen while the exhaust valves are shut tight, and a lot of that sound is absorbed by the surrounding metal and water jacket.
When the exhaust valves opens however, the hot expanding gasses enter the downpipes at high speed, and that produces more sound waves, which travel down the system more or less unimpeded by the restrictions in the downpipes.
The End Can, has different effects on fast moving gasses and sound waves. Most End Cans have a perforated metal tube running through the centre, which is surrounded by a sound-deadening material, or 'Wadding'. This allows the gasses to flow through, but the sound waves pass through the perforations and are absorbed by the Wadding.
The design considerations for an effective and efficient exhaust system, are that it should allow the burned gasses to escape from the combustion chamber quickly, allow them to expand and cool quickly, and absorb excessive noise before leaving the system. Some racing exhausts have a massively increased diameter in the downpipes,
When you have turbo-assisted or super-charged intakes, this is less of a design issue - and open pipes of consistent diameter work just fine (like Dragsters and aircraft engines) because the intake design allows for a certain amount of un-burned gasses under high pressure to pass into the exhaust system - and we want to get rid of them as fast as possible into the atmosphere to reduce the risk of explosion close to the engine.
The Vara's factory system doesn't do that! The physical reduction of the internal diameter of the downpipes prevent the gasses from expanding quickly enough to create a low pressure zone to assist the gasses behind to escape faster. The same restriction has little effect on the sound waves, other than changing the pitch.
Also, the factory End Can has physical baffles before and after the wadding, and a small exit stub - where most after-market Cans are 'straight through'.
The Carburettors are a whole new ball game, and need to be considered separately.
You have 'Demand' on one side, and 'Availability' on the other, with the carburettor in the middle, which has access to fresh air and a supply of fuel.
Demand is determined by the swept volume of the cylinder, which in this case is 62cc, and a 'throttle valve' between the carburettor and the engine to regulate it.
Availability is determined by the amount of fuel and air available - in this case, whatever fuel in in the tank and the size of the main jet in the carburettor, and the amount of air that can enter the carburettor from the atmosphere (which is limited by the intake bung and filter).
The carburettor has a variable main jet through which the fuel passes into the airstream, and the amount of fuel allowed through the jet is governed by a tapered needle attached to a piston, which rises and falls depending on the volume of air passing over the jet, which is regulated by the throttle valve.
On the Vara's front carburettor, the main jet and needle are optimised for a 62cc cylinder, but the rear carb is optimised for a 50cc cylinder - not difficult to do when you have 125cc and 50cc engines being produced at the same factory!
In theory, the best setup would be to have both carburettors configured the same as the front one - but is it worth it?
If we take it that the front carb is ideal for a 62cc cylinder, and the rear is ideal for a 50cc cylinder, then this setup should be able to produce 14.6bhp from a 112cc engine - but if both cylinders are the same, the front cylinder must be contributing 8.0822bhp to the total, whilst the rear is only contributing 6.517bhp. (14.6/112 x 62 and 14.6/112 x 50)
If we can make the rear the same as the front, we would have a theoretical maximum of just under 16.2bhp - an increase of just 1.6bhp, or about 11% - and that is just theory, assuming less than 0.01% tolerance. If you factor in wear and tear, less-than-perfect components and less-than-perfect conditions, I don't think it's worth the effort, time or cost.
If you wanted more power than that, you would have to start looking at the cylinder head design to increase the diameter of the inlet and exhaust valves, improve gas flow in and out, and also changing the camshaft profiles to make the valves open faster and stay open longer.
I would be happy for someone to prove me wrong on this, as I personally believe that 14.6bhp is not enough for safety on the road, unless you reduce the power in all other vehicles proportionally.
BTW - 'DB Killers' and Baffle Tubes that fit into the outlet of after-market End Cans, work by reflecting sound waves back into the End Can so they can be absorbed by the wadding, without adding to much of a restriction on the flow of gasses.
By the time the gasses reach the end can, they should have already expanded and cooled enough so that whatever happens now, won't have a massive effect on the power output of the engine.
I think we are getting off track here!
Generally, road legal aftermarket cans do not require rejetting & the bike will run fine.
By all means get a noisier exhaust, just don't have the assumption that cars will hear you and that will keep you safe - for that, you need observation, anticipation, moderation and a touch of good luck!
Remember that by having a noisy can, for every person that may be impressed there will be several that think you are a c0ck & motorbikes are a menace and should be banned. It's your choice :)
Yeah well said MR X
Quote from: Mr X on 08/10/14 - 10:38:45
Generally, road legal aftermarket cans do not require rejetting & the bike will run fine.
There is an increasing trend for people to make comments online without thinking about the consequences.
We recently had a thread on another forum from a Varadero owner who couldn't get his bike to start, probably due to stale fuel or gummed up carbs. I know a very good way of starting an engine to allow it to warm up which would probably have solved his problem. I didn't post anything because there is a risk associated with it and if he had an accident I would have some degree of liability.
Which bring me to my point :
If you say something on here like " aftermarket cans do not require rejetting & the bike will run fine" and someone does it and subsequently wrecks their engine, you could be held responsible !
A very fair and valid point, however, my comment was based on what many aftermarket exhaust manufacturers state in their advertising blurb. The fact that I started my comment with the word ''generally'' would suggest that it would be wise to check first.
Maybe forums should forbid for people to have input or suggestions?
People come on here to try and gain from the experience of others. It is what forums are for.
What we should always remember is that what you say might not be necessarily what the person who asked the question hears or interprets.
Saying it is wise to check first begs the question "who should you ask?".
The exhaust company who want to sell you something?
The anonymous contributor?
I try to understand what the post is all about and then try to give an opinion to solve the question.
In this case and in many other 125 queries I can understand the frustration of trying to improve the ride.
The answer is simple. Pass your test and buy a bigger bike. Live with what you have for now. Keep it stock so you can sell it on.
The Prodded Dog
Sorry but I can't help thinking that my reply was much more relevant to the initial post than the drivel that you posted.
Christ, no wonder this forum is dead if that's how contributors are treated.
Please delete my account, I'm outta here...
Quote from: Mr X on 10/10/14 - 11:37:54
Sorry but I can't help thinking that my reply was much more relevant to the initial post than the drivel that you posted.
Christ, no wonder this forum is dead if that's how contributors are treated.
Please delete my account, I'm outta here...
Done :)
Quote from: Mr X on 10/10/14 - 11:37:54
Sorry but I can't help thinking that my reply was much more relevant to the initial post than the drivel that you posted.
Christ, no wonder this forum is dead if that's how contributors are treated.
Please delete my account, I'm outta here...
Sorry to lose you so soon and thanks for your contribution.
The Podded Dog
Just out of curiosity, I asked a local tube bending specialist if they could duplicate the Vara's exhaust system, using 32mm stainless tube.
The guy took lots of measurements, then went off into the workshop to check they had the correct mandrels - and Yes! It can be done.
It would cost about ?150 for a one-off, plus about ?90 for the setup costs, tooling, and a minimum purchase of tube stock - but the setup costs could be absorbed in an order of 6 or more units.
The custom units would be from the cylinder heads to where the factory end-can joins, just above the right-hand footpeg hanger, so you could re-use the factory silencer, or add an after-market one with a suitable link pipe (which I forgot to ask a price for, but shouldn't be a huge cost).
It would be a case of one-size-fits-all, but with the option of adding a threaded boss for the O2 sensors on injection models.
Obviously, neither myself or the forum could accept responsibility if you buy one and fit it and something bad happens - but is there any interest out there?
I need to do something with mine soon as it is starting to get a bit rusty, but it would be nice to get the cost down to ?150.