Custom Muffler
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xtremelow
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You are going to want some type of back pressure. Running an empty pipe will have no restriction and be basically like running open headers. You will be losing power, and IMO you will be left with a hollow empty sound instead of a throaty roar.
Thats what i thought, i have it with a guy that a few people say he he knows what he is doing so i guess i will wait and see. Thanks for your input.
By the way, isnt that what a Jardine is? straight through, thats what i have just taken off my bike and i had plenty of power there...
By the way, isnt that what a Jardine is? straight through, thats what i have just taken off my bike and i had plenty of power there...
I believe that loss of back pressure isn't an issue as long as you re-tune your ECM.
Here's as good an explanation as I have found.
http://www.uucmotorwerks.com/html_product/sue462/backpressuretorquemyth.htm
What you may lose is scavenging.
I'm about to gut my own exhaust and I'm planning on putting a straight pipe from the header input going about 2/3 down the length of the exhaust body.
I think this should help keep the low end torque and sound good as well.
I'm also thinking about putting a short section of 'glass pack' baffle right before the exit.
Here's as good an explanation as I have found.
http://www.uucmotorwerks.com/html_product/sue462/backpressuretorquemyth.htm
What you may lose is scavenging.
I'm about to gut my own exhaust and I'm planning on putting a straight pipe from the header input going about 2/3 down the length of the exhaust body.
I think this should help keep the low end torque and sound good as well.
I'm also thinking about putting a short section of 'glass pack' baffle right before the exit.
crxtasy169
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It's not only scavenging you lose it's fuel and fresh air intake charge. There is actually a point where the intake and the exhaust valves are open at the same time just before the exhaust valve closes and as the intake valve is starting to open( it's called overlap). When there is no back pressure it allows the new incoming air/fuel charge to blow out the exhaust before it even gets used there fore losing efficiency in the engine, lower gas mileage, horsepower, and torque. Free flowing exhaust help but must have some back pressure or it will run like crap.
CoastieRider
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Public Service Announcement:
By RB Racing
Probably the best site ever..
We are going to state this very clearly...Backpressure does not increase horsepower. Period.
An often heard statement from the well-informed is "You need a bit of backpressure for an exhaust to work". Usually this comes from someone who is not a tuner or someone who is faced with a situation where he does not have the tools or means to adjust things. Anything you do in the exhaust will change the flows, the pressures, or velocities somewhat. The correct scenario is that the exhaust has to be properly designed and then you optimize the jetting, ecu data inputs, camshafts, port dimensions, valve sizes and the like. The exhaust has to be designed for the intended use.
This all dates from the early 1980's when Supertrapp invented a muffler designed for dirtbikes to trap potential sparks, or burning, carbonized, bits, so it could have US Forrestry Approval for off-road use. The "trapp" tells what the intended purpose was. If you wanted a Harley to barely work you had to stick a couple of pounds, or about 23-25 of these discs in the end of your exhaust. Of course this didn't really work, which is why they ended up putting a hole up the middle anyway. You don't tune an exhaust.
Your engine has 15 psi (1 Bar) of atmospheric pressure sitting at the inlet and another 15 psi lurking at the end of the tailpipe. The inlet stroke creates a pressure differential and the atmosphere goes rushing inward. The exhaust valve opens and there is a pressure rise in the tube followed by a strong vacuum signal as the gases head down the pipe. Note that we said "vacuum signal."
Pressure differentials can be seen in the exhaust of a jet engine. We have a high pressure pulse coming out our exhaust system but it's just not visible as in the photo above.
The pattern of evenly spaced rings sometimes visible in the exhaust of jet engine is typically referred to as shock diamonds or Mach disks. The phenomenon occurs anytime a flow exits a nozzle at supersonic speeds and at a pressure that is different than that of the external atmosphere. Most of us are probably used to seeing shock diamonds occur near sea level during the takeoff of an aircraft, like in the above photo of the SR-71 Blackbird.
Logical extremes are often used to illustrate a point. For those who argue that backpressure can be a help they might say, from an extreme position, "Let's throw away the exhaust system so we have no backpressure at all". They would then conclude that the motor would run like crap and we would agree completely. The only problem is that they haven't gotten rid of backpressure, they simply have introduced 15 psi at the exhaust port and have given up any inertia, gas speeds or vacuum signals that exist in a primary tube.
The vacuum signal or low pressure that follows an exhaust event can be used to help scavenge the cylinder during overlap when both exhaust and inlet valves are open. Conversely, during this overlap period, the increase in backpressure can cause these burnt gases to re-enter the combustion chamber and contaminate the inlet charge. Result...loss of power.
The proper way to look at exhausts is to view them as a way to maintain the highest velocity that will not impede flow. As velocity increases the pressure drops and the engine can become more efficient. We have all the variables of length, diameter, rpm, collector size, internal shapes and the reflective waves that all this causes. There is no "one answer".
For those of you who disagree because of anecdotal evidence we would agree with you also. Altering an exhaust's flow can correct someting else like mixure or spark timing. In the end, if you have to throw it off a cliff to win, do it. Only results count and if increasing backpressure helps your situation then do it.
As a final thought...Gale Banks doesn't make money selling increased backpressure exhaust systems. Think about it.
By RB Racing
Probably the best site ever..
We are going to state this very clearly...Backpressure does not increase horsepower. Period.
An often heard statement from the well-informed is "You need a bit of backpressure for an exhaust to work". Usually this comes from someone who is not a tuner or someone who is faced with a situation where he does not have the tools or means to adjust things. Anything you do in the exhaust will change the flows, the pressures, or velocities somewhat. The correct scenario is that the exhaust has to be properly designed and then you optimize the jetting, ecu data inputs, camshafts, port dimensions, valve sizes and the like. The exhaust has to be designed for the intended use.
This all dates from the early 1980's when Supertrapp invented a muffler designed for dirtbikes to trap potential sparks, or burning, carbonized, bits, so it could have US Forrestry Approval for off-road use. The "trapp" tells what the intended purpose was. If you wanted a Harley to barely work you had to stick a couple of pounds, or about 23-25 of these discs in the end of your exhaust. Of course this didn't really work, which is why they ended up putting a hole up the middle anyway. You don't tune an exhaust.
Your engine has 15 psi (1 Bar) of atmospheric pressure sitting at the inlet and another 15 psi lurking at the end of the tailpipe. The inlet stroke creates a pressure differential and the atmosphere goes rushing inward. The exhaust valve opens and there is a pressure rise in the tube followed by a strong vacuum signal as the gases head down the pipe. Note that we said "vacuum signal."
Pressure differentials can be seen in the exhaust of a jet engine. We have a high pressure pulse coming out our exhaust system but it's just not visible as in the photo above.
The pattern of evenly spaced rings sometimes visible in the exhaust of jet engine is typically referred to as shock diamonds or Mach disks. The phenomenon occurs anytime a flow exits a nozzle at supersonic speeds and at a pressure that is different than that of the external atmosphere. Most of us are probably used to seeing shock diamonds occur near sea level during the takeoff of an aircraft, like in the above photo of the SR-71 Blackbird.
Logical extremes are often used to illustrate a point. For those who argue that backpressure can be a help they might say, from an extreme position, "Let's throw away the exhaust system so we have no backpressure at all". They would then conclude that the motor would run like crap and we would agree completely. The only problem is that they haven't gotten rid of backpressure, they simply have introduced 15 psi at the exhaust port and have given up any inertia, gas speeds or vacuum signals that exist in a primary tube.
The vacuum signal or low pressure that follows an exhaust event can be used to help scavenge the cylinder during overlap when both exhaust and inlet valves are open. Conversely, during this overlap period, the increase in backpressure can cause these burnt gases to re-enter the combustion chamber and contaminate the inlet charge. Result...loss of power.
The proper way to look at exhausts is to view them as a way to maintain the highest velocity that will not impede flow. As velocity increases the pressure drops and the engine can become more efficient. We have all the variables of length, diameter, rpm, collector size, internal shapes and the reflective waves that all this causes. There is no "one answer".
For those of you who disagree because of anecdotal evidence we would agree with you also. Altering an exhaust's flow can correct someting else like mixure or spark timing. In the end, if you have to throw it off a cliff to win, do it. Only results count and if increasing backpressure helps your situation then do it.
As a final thought...Gale Banks doesn't make money selling increased backpressure exhaust systems. Think about it.
crxtasy169
Well-known member
- Joined
- Jun 20, 2009
- Messages
- 912
As the article above says yes it's true back pressure does not increase horsepower but it can decrease it and engine performance if you do not have enough.
BuellerPilot
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Thanks CoastiRider!
I've kept quiet about a lot of exhaust discussions here as to not ruffle some feathers. I've seen a LOT of misinformation being repeated. So here goes.....
NO, I repeat NO back pressure is not a friend in an exhaust system, at all PERIOD.
NO it does not increase power AT all with one exception.... unless your tune is off and you need to DECREASE the efficiency of your engine (READ" USE LESS FRESH AIR) to bring your mixture richer, then in this case you would notice a power INCREASE from resulting introduced back pressure. Note if you ADD FUEL instead of IMPEDE FLOW your power would INCREASE MORE then choking it up to band aid or make up for a lack of a proper tune.
Lets break it down a little more.
Your objection for an optimal exhaust system (lets throw out the mathematics and generalize here for discussion's sake) is to MAXIMIZE your VELOCITY of your exhaust gases exiting your exhaust pipe.
Your exhaust gas has weight/mass to it, therefore it carries an inertia. You want to use this inertia of your gas flow (mind you, your exhaust doesn't have a steady stream of gasses leaving it like a water hose, it's a violent series of pulses that constantly push and pull) to maximize it's pulling power behind it. When a puff of gas leaves your exhaust port, it's pressure is greater then the atmosphere it's headed toward (Duh!), it's fighting a pressure differential, and you want to minimize this differential (READ: MINIMIZE BACK PRESSURE) because as this "Puff" travels down the header it has a low pressure spot behind it. The higher the velocity, the more inertia, the bigger pull (or lower pressure wave) behind this puff of gas. This low pressure behind your puff is what you want to time so it's at your exhaust port during the overlap period (when both the intake and exhaust are open). You want to maximize your velocity without introducing impedance of flow. In other words, your going to want a smooth pipe that maximizes the gas velocity but not introduce to back pressure. This is were sizing both in diameter and length are important (length is important more for pulse and wave timing/tuning, and I won't get into that for THIS discussion). Your velocity will hit a ceiling on where it's being useful. So your pipe should be sized to maximize velocity yet minimize flow restrictions. It's a balance. What this means is a smooth pipe sized in diameter to get the high velocity, but not too small in diameter to impede flow. And gizmos in this pipe is strictly an inhibitor (such as rings welded in the pipe, muffler baffles, etc.).
Back pressure DOES NOT INCREASE TORQUE OR POWER PERIOD.
Lets use the same gas puff and keep a fixed volume. Squeeze it through a smaller diameter pipe, velocity increases (and therefore the inertia of the gas puff increases), and unfortunately back pressure does to. Now use a larger diameter pipe and the velocity drops and so does back pressure and thus you loose inertia also.
You want to keep inertia up not only for a stronger negative wave behind it, but also so it has a stronger punch when it exits the pipe and smacks head on with atmospheric pressure (14.7 PSI).
Lets run a scenario here for better understanding on the relationship of velocity and "Back pressure" and power production.
You size a pipe to maximize your low end. You'd pick a smaller diameter, you have less gases at the low end because you have less power strokes given in a certain time (RPM = Rev's Per Minute), so less gas is being carried by the pipe. So making it SMALLER will speed up it's VELOCITY so that gas carries more INERTIA so it has a stronger negative pressure wave behind it or "scavenging effect" so during over lap it has a better chance of pulling old burnt exhaust gases out of the cylinder to make more room for a fresher oxygen rich charge to take it's place and it has a stronger punch when it leave the pipe to hit the atmosphere. Now this same smaller diameter pipe becomes a restriction at higher RPM's (READ: BACK PRESSURE) because there's now a lot more gases in the pipe and the actual pipe diameter is too small to accommodate the amount of gases trying to pass through it. Your velocity has hit a ceiling and your now impeding flow at this point. You'd need to up size the pipe diameter to maximize flow yet STILL KEEP VELOCITY UP at higher RPM's. So lets not confuse what "Back pressure" did here. You got better low range RPM performance due to an increase of velocity because you have a smaller diameter pipe, your back pressure DID go up, but it was an unfortunate by-product and NOT the reason you'd be making more power. To summarize, smaller pipe kept the velocity up at lower RPM which kept inertia high for the exhaust gases which had a better scavenging effect which resulted in better low RPM cylinder filling and a cleaner cylinder full of fresher fuel/air. The pipe choked the top end impeding flow and causing exhaust gases to back up and not allow scavenging to happen properly and most likely had a phenomenon called "reversion" where exhaust that had left the cylinder are backing back up in the pipe and back up to a point where the gas that left the cylinder is now reverting and going back into the cylinder. Back pressure went up as a by-product and hurt high end power
Now lets reverse this scenario or play the opposite end. Your looking to make more power in the upper RPM's at the sacrifice of low RPM grunt. You'd go up in diameter of the pipe. Your upping the diameter because you have a lot more exhaust volume to deal with now and the smaller diameter pipe you previous had is choking your flow and your velocity has hit it's ceiling. You sized the diameter appropriately so you making full use of high velocity, but your not hitting the velocity ceiling so you flow is maximized resulting in LOW BACK PRESSURE. Your engine now screams at the top end, the high high velocity unimpeded gas pulse flow has lots of inertia to not only draw old exhaust gases from the cylinder but has enough umph to actually pull in fresh air and fuel from your intake system and pull it into your awaiting cylinder for a bigger bang on the compression stroke. But you lost low end power why?? Because that big pipe at low RPM where gas volume is lower doesn't keep the velocity up. The low gas volume is wasting it's expanding energy in filling up the volume of the pipe instead of expanding out of the pipe. This low velocity carries low inertia and the gas pulses actually stall in this big pipe. Now the next exhaust puff hit's the puff in front of it because it stalled in the pipe and we start getting a backing up of Puff's. Were not getting that strong negative wave so scavenging is none existent. We now have REVERSION and the exhaust gases rather than leaving the cylinder are backing back into it during overlap. In severe cases this exhaust can even back into the INTAKE MANIFOLD. You see this is BIG CAM engines where over lapped is really high and there isn't sufficient exhaust VELOCITY at LOW RPM to keep from reversing back into the cylinder and intake runners hence the cool "Lope Lope Lope" idle because the engine isn't getting enough fresh air and the cylinders are actually misfiring every other stroke or so do to a lack of fresh air with the fuel to ignite off.
On to more misinformation:
Straight through mufflers offer THE BEST PERFORMANCE in all situations given your header diameters, collectors, mid pipes and muffler core diameters are sized correctly PERIOD given you are TUNED for such systems. The ONLY, ONLY time your gaining power from a restriction (READ; BACK PRESSURE)is if your currently aren't tuned correctly and you impede flow (back pressure) to get your current tune to a better air/fuel ratio.
I've seen post of people complaining of a lack of low end power using the Jardine mufflers. This is NOT due to a lack of "Back Pressure", the loss in power is a LACK of FUEL. You made your engine system more EFFICIENT and it is puling in more air. If you don't add more fuel it won't make more power but will lose power due to being lean. Now I've seen some add a "cone" and even large washers just after the collector to "gain back low end torque", but the power increase they felt was because they DECREASED the efficiency (less gas going out, less air coming in) an brought their air/fuel ratios back to were the stock ECM is injection a metered fuel rate to. They didn't "increase power because they added Back pressure, they DECREASED power potential to fit there ECM's current tune. If they would just ADD FUEL to these lean spots, they would have GAINED much more power then what they perceived as a gain by adding that restriction/back pressure.
Running a hollow muffler will have SIGNIFICANT BACK PRESSURE, NOT the opposite as stated earlier by a poster above. It would have MUCH more back pressure than the straight through core muffler. It would be due to letting the exhaust gas coming out of the mid pipe suddenly coming to the empty LARGE VOLUME VOID of a gutted can and expanding loosing all velocity and STALLING in that huge empty chamber. All these stalled pulses back up and create BACK PRESSURE.
Perforated core mufflers offer VERY LITTLE BACK PRESSURE. It is even difficult to see any sort of difference on a dyno between a straight piece of pipe and a perforated core muffler. This is FACT. I'm talking about perforated cores, the straight pipe with holes in them. Now the type that are louvered are a different story, those can creat a LOT of back pressure, even more so then baffles.
Baffled mufflers are NOT "tuned" to create torque or power (funny, some don't even realize the relationship of torque and power), they are baffled to REDUCE SOUND and that's all. They might be optimized to have a good sound while attempting to MINIMIZE POWER and TORQUE LOSSES. The purpose of a muffler is to reduce sound, a muffler can NEVER make more power or torque ANYWHERE in a power band that a straight piece of tubing can do (granted everything is sized in diameter, length etc.). Again, their job is to reduce sound and/or change the note so it's more appealing to the human ear.
I hope this clarifies some things, keep in mind I generalized this into one post where theres antire libraries dedicated to this stuff. Theres a **** ton more to it like size, length, bends, even shapes of tubing (like the MICRON flat bends) and collector merge angles, collector volumes, diameters, expansion or megaphones ETC ETC. I didn't even touch on gas expansion and temperatures (like you want to keep it hot, and you want it to expand down the pipe, not in the pipe, etc.)
I'm not listing my opinions here, I'm listing FACTS as agreed by scientist, not back yard shade tree racers or engine builders (more like engine assemblers).
I didn't bring this post up to debate, as you can't debate facts, you can only debate facts if you don't understand them.
Read and read more and make sure you understand exhaust theories before debating anything lol, cause if you debate any of this or what CoastieRider says, then it's obvious you don't understand the facts. Not trying to be a dick or put anyone down, I just don't see a point in arguing with facts.
~Mike........
I've kept quiet about a lot of exhaust discussions here as to not ruffle some feathers. I've seen a LOT of misinformation being repeated. So here goes.....
NO, I repeat NO back pressure is not a friend in an exhaust system, at all PERIOD.
NO it does not increase power AT all with one exception.... unless your tune is off and you need to DECREASE the efficiency of your engine (READ" USE LESS FRESH AIR) to bring your mixture richer, then in this case you would notice a power INCREASE from resulting introduced back pressure. Note if you ADD FUEL instead of IMPEDE FLOW your power would INCREASE MORE then choking it up to band aid or make up for a lack of a proper tune.
Lets break it down a little more.
Your objection for an optimal exhaust system (lets throw out the mathematics and generalize here for discussion's sake) is to MAXIMIZE your VELOCITY of your exhaust gases exiting your exhaust pipe.
Your exhaust gas has weight/mass to it, therefore it carries an inertia. You want to use this inertia of your gas flow (mind you, your exhaust doesn't have a steady stream of gasses leaving it like a water hose, it's a violent series of pulses that constantly push and pull) to maximize it's pulling power behind it. When a puff of gas leaves your exhaust port, it's pressure is greater then the atmosphere it's headed toward (Duh!), it's fighting a pressure differential, and you want to minimize this differential (READ: MINIMIZE BACK PRESSURE) because as this "Puff" travels down the header it has a low pressure spot behind it. The higher the velocity, the more inertia, the bigger pull (or lower pressure wave) behind this puff of gas. This low pressure behind your puff is what you want to time so it's at your exhaust port during the overlap period (when both the intake and exhaust are open). You want to maximize your velocity without introducing impedance of flow. In other words, your going to want a smooth pipe that maximizes the gas velocity but not introduce to back pressure. This is were sizing both in diameter and length are important (length is important more for pulse and wave timing/tuning, and I won't get into that for THIS discussion). Your velocity will hit a ceiling on where it's being useful. So your pipe should be sized to maximize velocity yet minimize flow restrictions. It's a balance. What this means is a smooth pipe sized in diameter to get the high velocity, but not too small in diameter to impede flow. And gizmos in this pipe is strictly an inhibitor (such as rings welded in the pipe, muffler baffles, etc.).
Back pressure DOES NOT INCREASE TORQUE OR POWER PERIOD.
Lets use the same gas puff and keep a fixed volume. Squeeze it through a smaller diameter pipe, velocity increases (and therefore the inertia of the gas puff increases), and unfortunately back pressure does to. Now use a larger diameter pipe and the velocity drops and so does back pressure and thus you loose inertia also.
You want to keep inertia up not only for a stronger negative wave behind it, but also so it has a stronger punch when it exits the pipe and smacks head on with atmospheric pressure (14.7 PSI).
Lets run a scenario here for better understanding on the relationship of velocity and "Back pressure" and power production.
You size a pipe to maximize your low end. You'd pick a smaller diameter, you have less gases at the low end because you have less power strokes given in a certain time (RPM = Rev's Per Minute), so less gas is being carried by the pipe. So making it SMALLER will speed up it's VELOCITY so that gas carries more INERTIA so it has a stronger negative pressure wave behind it or "scavenging effect" so during over lap it has a better chance of pulling old burnt exhaust gases out of the cylinder to make more room for a fresher oxygen rich charge to take it's place and it has a stronger punch when it leave the pipe to hit the atmosphere. Now this same smaller diameter pipe becomes a restriction at higher RPM's (READ: BACK PRESSURE) because there's now a lot more gases in the pipe and the actual pipe diameter is too small to accommodate the amount of gases trying to pass through it. Your velocity has hit a ceiling and your now impeding flow at this point. You'd need to up size the pipe diameter to maximize flow yet STILL KEEP VELOCITY UP at higher RPM's. So lets not confuse what "Back pressure" did here. You got better low range RPM performance due to an increase of velocity because you have a smaller diameter pipe, your back pressure DID go up, but it was an unfortunate by-product and NOT the reason you'd be making more power. To summarize, smaller pipe kept the velocity up at lower RPM which kept inertia high for the exhaust gases which had a better scavenging effect which resulted in better low RPM cylinder filling and a cleaner cylinder full of fresher fuel/air. The pipe choked the top end impeding flow and causing exhaust gases to back up and not allow scavenging to happen properly and most likely had a phenomenon called "reversion" where exhaust that had left the cylinder are backing back up in the pipe and back up to a point where the gas that left the cylinder is now reverting and going back into the cylinder. Back pressure went up as a by-product and hurt high end power
Now lets reverse this scenario or play the opposite end. Your looking to make more power in the upper RPM's at the sacrifice of low RPM grunt. You'd go up in diameter of the pipe. Your upping the diameter because you have a lot more exhaust volume to deal with now and the smaller diameter pipe you previous had is choking your flow and your velocity has hit it's ceiling. You sized the diameter appropriately so you making full use of high velocity, but your not hitting the velocity ceiling so you flow is maximized resulting in LOW BACK PRESSURE. Your engine now screams at the top end, the high high velocity unimpeded gas pulse flow has lots of inertia to not only draw old exhaust gases from the cylinder but has enough umph to actually pull in fresh air and fuel from your intake system and pull it into your awaiting cylinder for a bigger bang on the compression stroke. But you lost low end power why?? Because that big pipe at low RPM where gas volume is lower doesn't keep the velocity up. The low gas volume is wasting it's expanding energy in filling up the volume of the pipe instead of expanding out of the pipe. This low velocity carries low inertia and the gas pulses actually stall in this big pipe. Now the next exhaust puff hit's the puff in front of it because it stalled in the pipe and we start getting a backing up of Puff's. Were not getting that strong negative wave so scavenging is none existent. We now have REVERSION and the exhaust gases rather than leaving the cylinder are backing back into it during overlap. In severe cases this exhaust can even back into the INTAKE MANIFOLD. You see this is BIG CAM engines where over lapped is really high and there isn't sufficient exhaust VELOCITY at LOW RPM to keep from reversing back into the cylinder and intake runners hence the cool "Lope Lope Lope" idle because the engine isn't getting enough fresh air and the cylinders are actually misfiring every other stroke or so do to a lack of fresh air with the fuel to ignite off.
On to more misinformation:
Straight through mufflers offer THE BEST PERFORMANCE in all situations given your header diameters, collectors, mid pipes and muffler core diameters are sized correctly PERIOD given you are TUNED for such systems. The ONLY, ONLY time your gaining power from a restriction (READ; BACK PRESSURE)is if your currently aren't tuned correctly and you impede flow (back pressure) to get your current tune to a better air/fuel ratio.
I've seen post of people complaining of a lack of low end power using the Jardine mufflers. This is NOT due to a lack of "Back Pressure", the loss in power is a LACK of FUEL. You made your engine system more EFFICIENT and it is puling in more air. If you don't add more fuel it won't make more power but will lose power due to being lean. Now I've seen some add a "cone" and even large washers just after the collector to "gain back low end torque", but the power increase they felt was because they DECREASED the efficiency (less gas going out, less air coming in) an brought their air/fuel ratios back to were the stock ECM is injection a metered fuel rate to. They didn't "increase power because they added Back pressure, they DECREASED power potential to fit there ECM's current tune. If they would just ADD FUEL to these lean spots, they would have GAINED much more power then what they perceived as a gain by adding that restriction/back pressure.
Running a hollow muffler will have SIGNIFICANT BACK PRESSURE, NOT the opposite as stated earlier by a poster above. It would have MUCH more back pressure than the straight through core muffler. It would be due to letting the exhaust gas coming out of the mid pipe suddenly coming to the empty LARGE VOLUME VOID of a gutted can and expanding loosing all velocity and STALLING in that huge empty chamber. All these stalled pulses back up and create BACK PRESSURE.
Perforated core mufflers offer VERY LITTLE BACK PRESSURE. It is even difficult to see any sort of difference on a dyno between a straight piece of pipe and a perforated core muffler. This is FACT. I'm talking about perforated cores, the straight pipe with holes in them. Now the type that are louvered are a different story, those can creat a LOT of back pressure, even more so then baffles.
Baffled mufflers are NOT "tuned" to create torque or power (funny, some don't even realize the relationship of torque and power), they are baffled to REDUCE SOUND and that's all. They might be optimized to have a good sound while attempting to MINIMIZE POWER and TORQUE LOSSES. The purpose of a muffler is to reduce sound, a muffler can NEVER make more power or torque ANYWHERE in a power band that a straight piece of tubing can do (granted everything is sized in diameter, length etc.). Again, their job is to reduce sound and/or change the note so it's more appealing to the human ear.
I hope this clarifies some things, keep in mind I generalized this into one post where theres antire libraries dedicated to this stuff. Theres a **** ton more to it like size, length, bends, even shapes of tubing (like the MICRON flat bends) and collector merge angles, collector volumes, diameters, expansion or megaphones ETC ETC. I didn't even touch on gas expansion and temperatures (like you want to keep it hot, and you want it to expand down the pipe, not in the pipe, etc.)
I'm not listing my opinions here, I'm listing FACTS as agreed by scientist, not back yard shade tree racers or engine builders (more like engine assemblers).
I didn't bring this post up to debate, as you can't debate facts, you can only debate facts if you don't understand them.
Read and read more and make sure you understand exhaust theories before debating anything lol, cause if you debate any of this or what CoastieRider says, then it's obvious you don't understand the facts. Not trying to be a dick or put anyone down, I just don't see a point in arguing with facts.
~Mike........
BuellerPilot
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- Jul 19, 2010
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- 1,226
Wow, didn't realize I wrote a book lol, sorry for it's length!
~Mike......
~Mike......
dave_xb12r
Well-known member
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- May 19, 2008
- Messages
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Sorry Mike, but the word "PERIOD" and all caps doesn't make it true. There is some good information here, but there is also some misleading. I'm not an expert, but I do know a little about how these things work.
I'm not going to type up an essay, so here is the short version. Our motors were designed to have back pressure. Unless you're changing out a lot of internals and doing major fuel and timing remapping, having no back pressure isn't beneficial. I like my back pressure and I'll keep it, thank you very much.
I'm not going to type up an essay, so here is the short version. Our motors were designed to have back pressure. Unless you're changing out a lot of internals and doing major fuel and timing remapping, having no back pressure isn't beneficial. I like my back pressure and I'll keep it, thank you very much.
BuellerPilot
Well-known member
- Joined
- Jul 19, 2010
- Messages
- 1,226
Dave,
If the back pressure works for you, then keep it.
I'm not telling anybody here how run their exhaust or what to do with their bikes. I'm explaining how an exhaust system should work to maximize a given perimeter or goal and am showing how one might *perceive* "back pressure" helping them.
What in particular would be "misleading" in my post?
BTW, our engines were designed in to 50's before exhaust tuning was fully understood, that doesn't mean that current rules of physics don't apply to them and the current engine was designed around many parameters to function as the factory intended taking fuel mileage, noise, emissions and performance into account.
~Mike.....
If the back pressure works for you, then keep it.
I'm not telling anybody here how run their exhaust or what to do with their bikes. I'm explaining how an exhaust system should work to maximize a given perimeter or goal and am showing how one might *perceive* "back pressure" helping them.
What in particular would be "misleading" in my post?
BTW, our engines were designed in to 50's before exhaust tuning was fully understood, that doesn't mean that current rules of physics don't apply to them and the current engine was designed around many parameters to function as the factory intended taking fuel mileage, noise, emissions and performance into account.
~Mike.....
dave_xb12r
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I would argue "Back pressure DOES NOT INCREASE TORQUE OR POWER PERIOD" because straight pipes decrease torque
BuellerPilot
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But they increase power yes?
dave_xb12r
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More back pressure does not equal more torque, Obviously you'll only get so much, but some back pressure is required, just not A LOT. Normally, by adding back pressure, you loose high end HP, but gain low end torque. That is what exhaust tuning is for; finding that sweet spot that you like. Good torque + good HP. You'll never have max both. I dont care about top end HP. I would rather have torque so I would rather have back pressure
BuellerPilot
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You didn't really read my post did you? [confused]
You got the basic down sort of, but your misunderstanding or using incorrectly the word "Back Pressure".
And power is function of torque over time. You cannot increase one without the other increasing also, you can only shift it around in the RPM range.
It's terms like "torque" and "power" and "back pressure" that are being miss-used and miss-understood that add to not fully understanding the dynamics of whats really going on in your exhaust system.
Lets not confuse good low end power/torque as being labeled "torque" and an engine that makes it's torque higher in the RPM range as being labeled "power". They are one in the same. You cannot have a measurement of "power" without torque (force). The word "Torque" does not mean an engine makes good low RPM grunt. It simply makes it's torque in the low RPM range. Same with an all top end engine. It should not be the winner for being labeled as "power" even though it does, it makes it's torque higher in the RPM range.
Lets not confuse an exhaust better suited for low end torque as being as such because "back pressure". That exhaust better suited for low end power/torque makes that power as a result of having a higher gas velocity at low RPM. Back pressure is a negative bi-product of that and the back pressure doesn't show up till you reach higher RPM's and starts to choke the top end. This is why it's mistakenly thought of as "back pressure is good for the low end". That back pressure didn't even show up till the exhaust gases started to be restricted hurting power (at the higher RPM).
Conversely, an exhaust designed for high end power/torque (can't have high power without high torque if your RPM ceiling isn't raised) will have little back pressure both in high and low RPM's, but it's NOT the lack of back pressure that kills the low end torque/power. It's the lack of exhaust velocity that killed it. So it can be mistaken and is incorrect to assume that a low back pressure exhaust makes no torque. This is wrong, it's not the lack of back pressure doing it, it's the lack of gas velocity at low RPM.
I hope this clarifies it. Even if some insist on using these terms incorrectly, I hope this little post at least helped to understand some of the dynamics that's going on inside those pipes.
I'm not attacking you Dave or anyone else personally, I'm just making an attempt to show the fundamentals and facts about exhaust tuning for everyone who wants to read/learn about it like CoastieRider touched on and debunking a lot of misinformation being repeated. I'm not stating anything different then he did, I just went a tad more in-depth and tried to explain it more. Those who choose to bury their heads in sand can do so, no skin off my behind lol.
I'm not a know-it-all (honestly, there is no such person), but I have done quit a bit of studying and research on this subject. I have an office at NASA Langley and though my field is UAV's (unmanned Air vehicles) I have done a lot of internal combustion work and research both in my employment and because I'm a gear head on my personal time as well. I'm also surrounded by some of the greatest minds on earth at NASA for me to pick and listen too.
~Mike......
You got the basic down sort of, but your misunderstanding or using incorrectly the word "Back Pressure".
And power is function of torque over time. You cannot increase one without the other increasing also, you can only shift it around in the RPM range.
It's terms like "torque" and "power" and "back pressure" that are being miss-used and miss-understood that add to not fully understanding the dynamics of whats really going on in your exhaust system.
Lets not confuse good low end power/torque as being labeled "torque" and an engine that makes it's torque higher in the RPM range as being labeled "power". They are one in the same. You cannot have a measurement of "power" without torque (force). The word "Torque" does not mean an engine makes good low RPM grunt. It simply makes it's torque in the low RPM range. Same with an all top end engine. It should not be the winner for being labeled as "power" even though it does, it makes it's torque higher in the RPM range.
Lets not confuse an exhaust better suited for low end torque as being as such because "back pressure". That exhaust better suited for low end power/torque makes that power as a result of having a higher gas velocity at low RPM. Back pressure is a negative bi-product of that and the back pressure doesn't show up till you reach higher RPM's and starts to choke the top end. This is why it's mistakenly thought of as "back pressure is good for the low end". That back pressure didn't even show up till the exhaust gases started to be restricted hurting power (at the higher RPM).
Conversely, an exhaust designed for high end power/torque (can't have high power without high torque if your RPM ceiling isn't raised) will have little back pressure both in high and low RPM's, but it's NOT the lack of back pressure that kills the low end torque/power. It's the lack of exhaust velocity that killed it. So it can be mistaken and is incorrect to assume that a low back pressure exhaust makes no torque. This is wrong, it's not the lack of back pressure doing it, it's the lack of gas velocity at low RPM.
I hope this clarifies it. Even if some insist on using these terms incorrectly, I hope this little post at least helped to understand some of the dynamics that's going on inside those pipes.
I'm not attacking you Dave or anyone else personally, I'm just making an attempt to show the fundamentals and facts about exhaust tuning for everyone who wants to read/learn about it like CoastieRider touched on and debunking a lot of misinformation being repeated. I'm not stating anything different then he did, I just went a tad more in-depth and tried to explain it more. Those who choose to bury their heads in sand can do so, no skin off my behind lol.
I'm not a know-it-all (honestly, there is no such person), but I have done quit a bit of studying and research on this subject. I have an office at NASA Langley and though my field is UAV's (unmanned Air vehicles) I have done a lot of internal combustion work and research both in my employment and because I'm a gear head on my personal time as well. I'm also surrounded by some of the greatest minds on earth at NASA for me to pick and listen too.
~Mike......
dave_xb12r
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I've always understood HP as more of momentum and torque is the force that builds the momentum. Yes, to have HP, torque must be present as well, but isn't the an optimum point right before one of those variables falls?
Also, because of our small RPM range, isn't it ideal to have your torque in the low range so that power builds faster? So wouldn't it be beneficial to have an exhaust that enables low end "torque"
Also, because of our small RPM range, isn't it ideal to have your torque in the low range so that power builds faster? So wouldn't it be beneficial to have an exhaust that enables low end "torque"
BuellerPilot
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The answer would be YES if your gearing is correct and your main objective is acceleration only.
Torque is a measurement of static force. More specifically it's a force around an axis (bending force if you will) Such as Foot Pounds (actually stated pounds feet). That force is specified as Foot.... Pounds. It's measured a foot (12 inches) from a pivot point and pounds of force (using gravity as a standard for weight {pounds}). Horse power is a measurement of work being done over time. Remember, torque is a force, or static force and is potential work. No work is being done though because nothing is moving, once again, its a static force. Now you take this static force and allow it into motion (axial or spinning about an axis) and now your measuring power or horse power (force over time, or work over time).
If your torque rises, stays the same, or even falls off slightly, your power measurement still climbs because your doing more work in the same amount of time (RPM INCREASE). Your power will decline eventually when torques falls off a good amount. It's just the way math works, and all this is based on math (physics!).
To convert torque to horsepower you simply multiply torque by rpm/5,252
That's why looking at Dyno plots you will ALWAYS see torque and Horsepower intersect at 5252 RPM's (granted your using the same scaling for both). This is also why typically in conventional gasoline engines you see Horsepower generally is higher then torque numbers. Because your multiplying torque by RPM. This is also why typically in Diesel engines you see Torque numbers higher then HP, this is because they typically don't rev to or much higher then 5000 RPM's (The cross over point).
1 HP = 33,000 ft·lb/min
hope this helps.......
~Mike.......
