Final exhaust discussion thread
05-15-03, 12:15 AM
#1
...94% correct.
Thread Starter
Final exhaust discussion thread
I previously wrote this post for another forum with info gathered from several different sources. This is solely intended to teach basic ideas, as trying to get a precise explanation of how to set a system up for maximum performance on every car would not be possible. Also, my information is gathered from people who have real experience and have real numbers to back up their ideas and opinions. If you find something written in here that is questionable please do not ppost the arguement, simply email or PM me with sources or phone numbers backing up your claim that the info is inaccurate and I will handle it accordingly. So here it is and thank you to everyone who helped and all that will contribute.
__________________________________________
__________________________________________
The Basic Idea
The basic idea of an exhaust system is to maximize the performance output to one’s desired level. There are hundreds upon hundreds of ways someone can tinker with their under-car concoctions to achieve something that they feel is good for them. This ranges from putting a shinny tip on their stock muffler to constructing a custom setup from the header/turbo to the point of exit. This is my attempt to shed a little bit of light onto this matter so that people out there will have a better idea of what to do to achieve their own goals.
I’m dividing this off into two main sections…NA Exhausts and Turbo Exhausts.
NA Exhaust Systems
This is the most extensive area on this matter as forced induction vehicles are less touchy to changes in the exhaust system.
First you have to understand what you’re trying to accomplish when you start a project like this. You need to know whether you just want it to look good, or you want to get real numbers out of it, or if you want to achieve the maximum amount of performance obtainable. After you decide that you have a good footing on where to start.
Typical thing’s you’ll need to construct your own exhaust system (keeping in mind the MKIII Supra as the guinea car) will be about 10-15’ of tubing in desired diameter and a muffler. Depending on what you want to do you may also need a catalytic converter in the same size as your tubing and a resonator also in the same size. You’ll need access to a welder and plenty of rods as well as a metal cut-off saw (easiest) or some other means of cutting metal. You may also want to use some ¼” mild steel plating to construct your mounting flanges on, but the stock flanges are usually easily cut and reused.
There are three major types of exhaust setups, in my own phrasing they are sport, street, and race.
Sport…looks
A “sport” setup is very simple and is usually only intended to add visual performance. A sport system is typically an aftermarket muffler welded to stock plumbing. No real gains are expected from this type, and the only changes are in appearance and volume. Most of these don’t change the sound of the car a great deal, only make it louder. Of course the loss of a restrictive stock muffler will help flow, thus slightly increasing HP...but not much.
Street…want to get real numbers out of it
A street exhaust gets a little more complicated and usually consists of plumbing from the catalytic converter back (cat-back). A street exhaust is installed with the intention of gaining real performance. The idea behind constructing or purchasing a street exhaust setup is to gain performance while remaining perfectly street-legal. Now diameter of tubing is a major concern when trying to accomplish real numbers, the following is roughly the sizes that should be used:
Liters_______Size of tubing
1................... 1.25" is decent for a
1.5................ 1.75"
2................... 2-2.25"
2.5 or 13B..... 2.25"
3....................2.25-2.5"
3.5 or 20B......2.5"
4....................2.75"
4.5.................2.75-3"
5....................3"
5.5.................3-3.25"
6....................3.25-2.75
Keep in mind that you don't want to go too large on an NA engine because back pressure does help you throught the power band, and too little will make your car suffer. But beings there is still a cat on the car (usually) then you shouldn't have to worry about that.
Now the basic build of this type of exhaust is to keep the moddified section of the exhaust fairly restriction free. When trying to get the best performance attainable from the setup you should use mandrel bends and a straight through style muffler. You want to make sure that all of the welds are smoother and the muffler is the same size as your tubing.
Race…maximum obtainable performance
A race style setup is typically an all-out replacement of the entire stock setup from the exhaust ports to the point of exit. One usually starts by installing a freer flowing exhasut manifold or headers. From there a straight piece of the desired size tubing is installed...this piece needs to be as long as possible without a bend in it. Another common method is to install a long radius 90* mandrel bend right after the header and dump the exhaust out the side. A muffler isn’t used unless the driver doesn’t like the sound. I personally built a silencer to fit in mine should I have company in the car or if I’m driving late at night.
Now, for a brief lesson in “Backpressure”.
Backpressure is a necessity with an NA engine. Those who say it isn’t necessary are free to email me links to sites that prove it or phone numbers to professionals who can back the point up. Backpressure is what maintains the velocity of the exhaust gas leaving the vehicle, backpressure also creates a scavenging effect essentially sucking an extra amount of spent gas from the combustion chamber when the exhaust port is open.
However, too much backpressure will hinder your car’s performance. A term that is more important word to focus on here is ‘volume’. Backpressure governs exhaust gas velocity and velocity and tubing size govern the volume of gas moved. For example: Small tubing=high velocity but high backpressure as well, these combined limit the volume of gas moved from engine to atmosphere in a given amount of time. Too small tubing will begin to decrease the velocity but the backpressure will still rise. Extra large tubing=low velocity and extremely low backpressure, these combined move exhaust gasses very slowly. Both of these move poor volumes of exhaust gasses, though better than too small a tubing. The ideal size tubing will be able to move the maximum amount of exhaust gasses out in a given amount of time.
Another point to look at though is what is the car used for…this changes the ideal tubing size. The size in tubing, after the exhaust has been completely freed up (tubing must at least be the same size as exhaust ports to be considered "freed up"), doesn’t change the peek power…it only moves it around in the RPM band. For example, 2.5” keeps the peek power of the 7M-GE 3liter NA supra within obtainable limits…that size tubing raises the power band (torque to be specific) 500-1000rpm higher than stock. A smaller diameter tubing will lower it and larger will raise it even higher. If you intend to keep your NA engine revved high and raced there then larger tubing might be a consideration. If you never race, or race often from a dig, then smaller tubing may be more ideal for you. again, after the exhaust is free, the only thing tubing size does is regulate where the power band will be.
CATS ARE NOT ALWAYS BAD when it comes to a racing or free flowing exhaust. As Waynis on Supraforums can vouch, the addition of a cat in a free flowing exhaust will not hinder flow so much as raise back pressure. The raising of the back pressure simply lowered the power band back down to a more streetable level, making the car more ideal for dig and drag (and other low RPM) racing. An ultra free flowing straight exhaust is intended for someone who either tries to get the highest speed possible from the vehicle or who races consistantly high in the RPM band, but that type of exhaust will hinder low end acceleration...for example:
My car=7MGE Supra NA
cat back (and a few other mods)
15.3 quarter mile and a top speed of 138 (or so, can't really remember)
free exhaust
15.7 quarter and a top speed of 147mph
Forced Induction Exhaust Systems
Turbo systems are much easier to construct with much fewer components to consider. In just about any application 3” tubing coupled with a straight-through muffler is the best setup…no cats, no resonators. Keep in mind that the turbo itself acts as a restriction in the exhaust so the freest flowing enviroment possible is required to achieve maximum output. But similar setups as stated above still apply. A sport following the same characteristics as stated above. A street type being a 3” cat-back with minimal bends. Then a race type being 3” from the turbo to the exit point with minimal bends.
There are really no tricks or anything to worry about. The freest possible exhaust is the best for a turbo application.
Please post questions or comments or PM them to me and I will get back with you as soon as possible.
Thank you
__________________________________________
Keep in mind that this was written up in regards to piston engines, but the same basics apply to the rotory.
__________________________________________
__________________________________________
The Basic Idea
The basic idea of an exhaust system is to maximize the performance output to one’s desired level. There are hundreds upon hundreds of ways someone can tinker with their under-car concoctions to achieve something that they feel is good for them. This ranges from putting a shinny tip on their stock muffler to constructing a custom setup from the header/turbo to the point of exit. This is my attempt to shed a little bit of light onto this matter so that people out there will have a better idea of what to do to achieve their own goals.
I’m dividing this off into two main sections…NA Exhausts and Turbo Exhausts.
NA Exhaust Systems
This is the most extensive area on this matter as forced induction vehicles are less touchy to changes in the exhaust system.
First you have to understand what you’re trying to accomplish when you start a project like this. You need to know whether you just want it to look good, or you want to get real numbers out of it, or if you want to achieve the maximum amount of performance obtainable. After you decide that you have a good footing on where to start.
Typical thing’s you’ll need to construct your own exhaust system (keeping in mind the MKIII Supra as the guinea car) will be about 10-15’ of tubing in desired diameter and a muffler. Depending on what you want to do you may also need a catalytic converter in the same size as your tubing and a resonator also in the same size. You’ll need access to a welder and plenty of rods as well as a metal cut-off saw (easiest) or some other means of cutting metal. You may also want to use some ¼” mild steel plating to construct your mounting flanges on, but the stock flanges are usually easily cut and reused.
There are three major types of exhaust setups, in my own phrasing they are sport, street, and race.
Sport…looks
A “sport” setup is very simple and is usually only intended to add visual performance. A sport system is typically an aftermarket muffler welded to stock plumbing. No real gains are expected from this type, and the only changes are in appearance and volume. Most of these don’t change the sound of the car a great deal, only make it louder. Of course the loss of a restrictive stock muffler will help flow, thus slightly increasing HP...but not much.
Street…want to get real numbers out of it
A street exhaust gets a little more complicated and usually consists of plumbing from the catalytic converter back (cat-back). A street exhaust is installed with the intention of gaining real performance. The idea behind constructing or purchasing a street exhaust setup is to gain performance while remaining perfectly street-legal. Now diameter of tubing is a major concern when trying to accomplish real numbers, the following is roughly the sizes that should be used:
Liters_______Size of tubing
1................... 1.25" is decent for a
1.5................ 1.75"
2................... 2-2.25"
2.5 or 13B..... 2.25"
3....................2.25-2.5"
3.5 or 20B......2.5"
4....................2.75"
4.5.................2.75-3"
5....................3"
5.5.................3-3.25"
6....................3.25-2.75
Keep in mind that you don't want to go too large on an NA engine because back pressure does help you throught the power band, and too little will make your car suffer. But beings there is still a cat on the car (usually) then you shouldn't have to worry about that.
Now the basic build of this type of exhaust is to keep the moddified section of the exhaust fairly restriction free. When trying to get the best performance attainable from the setup you should use mandrel bends and a straight through style muffler. You want to make sure that all of the welds are smoother and the muffler is the same size as your tubing.
Race…maximum obtainable performance
A race style setup is typically an all-out replacement of the entire stock setup from the exhaust ports to the point of exit. One usually starts by installing a freer flowing exhasut manifold or headers. From there a straight piece of the desired size tubing is installed...this piece needs to be as long as possible without a bend in it. Another common method is to install a long radius 90* mandrel bend right after the header and dump the exhaust out the side. A muffler isn’t used unless the driver doesn’t like the sound. I personally built a silencer to fit in mine should I have company in the car or if I’m driving late at night.
Now, for a brief lesson in “Backpressure”.
Backpressure is a necessity with an NA engine. Those who say it isn’t necessary are free to email me links to sites that prove it or phone numbers to professionals who can back the point up. Backpressure is what maintains the velocity of the exhaust gas leaving the vehicle, backpressure also creates a scavenging effect essentially sucking an extra amount of spent gas from the combustion chamber when the exhaust port is open.
However, too much backpressure will hinder your car’s performance. A term that is more important word to focus on here is ‘volume’. Backpressure governs exhaust gas velocity and velocity and tubing size govern the volume of gas moved. For example: Small tubing=high velocity but high backpressure as well, these combined limit the volume of gas moved from engine to atmosphere in a given amount of time. Too small tubing will begin to decrease the velocity but the backpressure will still rise. Extra large tubing=low velocity and extremely low backpressure, these combined move exhaust gasses very slowly. Both of these move poor volumes of exhaust gasses, though better than too small a tubing. The ideal size tubing will be able to move the maximum amount of exhaust gasses out in a given amount of time.
Another point to look at though is what is the car used for…this changes the ideal tubing size. The size in tubing, after the exhaust has been completely freed up (tubing must at least be the same size as exhaust ports to be considered "freed up"), doesn’t change the peek power…it only moves it around in the RPM band. For example, 2.5” keeps the peek power of the 7M-GE 3liter NA supra within obtainable limits…that size tubing raises the power band (torque to be specific) 500-1000rpm higher than stock. A smaller diameter tubing will lower it and larger will raise it even higher. If you intend to keep your NA engine revved high and raced there then larger tubing might be a consideration. If you never race, or race often from a dig, then smaller tubing may be more ideal for you. again, after the exhaust is free, the only thing tubing size does is regulate where the power band will be.
CATS ARE NOT ALWAYS BAD when it comes to a racing or free flowing exhaust. As Waynis on Supraforums can vouch, the addition of a cat in a free flowing exhaust will not hinder flow so much as raise back pressure. The raising of the back pressure simply lowered the power band back down to a more streetable level, making the car more ideal for dig and drag (and other low RPM) racing. An ultra free flowing straight exhaust is intended for someone who either tries to get the highest speed possible from the vehicle or who races consistantly high in the RPM band, but that type of exhaust will hinder low end acceleration...for example:
My car=7MGE Supra NA
cat back (and a few other mods)
15.3 quarter mile and a top speed of 138 (or so, can't really remember)
free exhaust
15.7 quarter and a top speed of 147mph
Forced Induction Exhaust Systems
Turbo systems are much easier to construct with much fewer components to consider. In just about any application 3” tubing coupled with a straight-through muffler is the best setup…no cats, no resonators. Keep in mind that the turbo itself acts as a restriction in the exhaust so the freest flowing enviroment possible is required to achieve maximum output. But similar setups as stated above still apply. A sport following the same characteristics as stated above. A street type being a 3” cat-back with minimal bends. Then a race type being 3” from the turbo to the exit point with minimal bends.
There are really no tricks or anything to worry about. The freest possible exhaust is the best for a turbo application.
Please post questions or comments or PM them to me and I will get back with you as soon as possible.
Thank you
__________________________________________
Keep in mind that this was written up in regards to piston engines, but the same basics apply to the rotory.
05-15-03, 12:45 AM
#2
...94% correct.
Thread Starter
Another lesson in back pressure...
I had an interesting question asked and this was my response...
Exhaust gasses flowing through the exhaust tubing encounter resistance against the walls. This resistance is called backpressure...other things cause back pressure as well such as a cat and type of muffler...but it is impossible to elliminate it withough having the gasses come straight out of the valves into the atmosphere.
Okay, that's how back pressure is created...this is what it does...
If you put your finger into a bowl of water you will clearly be able to see the ripples you caused flow out and then against the rim of the bowl. This is similar to what happens when exhaust gasses flow out against the walls of the tubing and into obstructions...it's ripples, and here, as they did in the bowl of water, bounce off and go back the way they came. So some of your exhaust gas pressure gets reflected back at the valves in negative waves...by the time that these waves make it back to the valve it's closed, and they bounce off become positive waves again. As they begine their travel back down the exhaust tubing they creat a suction between them and the closed exhaust valve. This suction pulls the new exhaust gasses out when the valve opens at a higher rate of speed than they would under normal circumstances...this is called scavenging. This process will repeat again and again every time the exhaust valve opens.
The scavenging effect causes a greater volume of exhaust gasses to travel through the tubing, and this is beneficial to the performance of the engine.
A stock FC exhaust has too small a diameter of tubing which causes a lot of back pressure, then three cats which cause a lot of back pressure, and two mufflers which cause a lot of back pressure. All of these obstructions send the pressure waves back to the valves at random crazy times when the valve is closed and and when it's open which causes the scavenging effect to be hindered, lowering the volume that can be moved. But a straight obstructionless exhaust will not send many waves back at all which hinders the scavenging effect...however, if the tubing size just happens to be too large then it will just take a higher volume of gasses to put the scavenging effect into full yield, which means the engine has to rev higher (hence the reason they put 2.5" exhausts on ITRs...they can rev that high).
This is why exhaust tuning is so difficult and varies so much from car to car to purpose to purpose. The differences in the obstructions and the distance between the valves and obstructions and such change the cars powerband. Hope this helps you out. Oh yeah, and I know rotories do not have valves, but the rotor works the process out in the same manner.
I had an interesting question asked and this was my response...
Exhaust gasses flowing through the exhaust tubing encounter resistance against the walls. This resistance is called backpressure...other things cause back pressure as well such as a cat and type of muffler...but it is impossible to elliminate it withough having the gasses come straight out of the valves into the atmosphere.
Okay, that's how back pressure is created...this is what it does...
If you put your finger into a bowl of water you will clearly be able to see the ripples you caused flow out and then against the rim of the bowl. This is similar to what happens when exhaust gasses flow out against the walls of the tubing and into obstructions...it's ripples, and here, as they did in the bowl of water, bounce off and go back the way they came. So some of your exhaust gas pressure gets reflected back at the valves in negative waves...by the time that these waves make it back to the valve it's closed, and they bounce off become positive waves again. As they begine their travel back down the exhaust tubing they creat a suction between them and the closed exhaust valve. This suction pulls the new exhaust gasses out when the valve opens at a higher rate of speed than they would under normal circumstances...this is called scavenging. This process will repeat again and again every time the exhaust valve opens.
The scavenging effect causes a greater volume of exhaust gasses to travel through the tubing, and this is beneficial to the performance of the engine.
A stock FC exhaust has too small a diameter of tubing which causes a lot of back pressure, then three cats which cause a lot of back pressure, and two mufflers which cause a lot of back pressure. All of these obstructions send the pressure waves back to the valves at random crazy times when the valve is closed and and when it's open which causes the scavenging effect to be hindered, lowering the volume that can be moved. But a straight obstructionless exhaust will not send many waves back at all which hinders the scavenging effect...however, if the tubing size just happens to be too large then it will just take a higher volume of gasses to put the scavenging effect into full yield, which means the engine has to rev higher (hence the reason they put 2.5" exhausts on ITRs...they can rev that high).
This is why exhaust tuning is so difficult and varies so much from car to car to purpose to purpose. The differences in the obstructions and the distance between the valves and obstructions and such change the cars powerband. Hope this helps you out. Oh yeah, and I know rotories do not have valves, but the rotor works the process out in the same manner.
05-15-03, 08:08 PM
#5
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I'm trying to find an article i once put together on delta pressure vs. velocity. You want to have the least delta pressure, with the most velocity for HP. And i'm too lazy to try to explain anything else tonight.
05-16-03, 10:13 AM
#7
Nice write up but I'll have to disagree with where you put the 13B and 20B in relation to exhaust tubing size. Its a little larger than you think. Depending on how you do the exhaust sleeves in the engine you will want anywhere from a 1 3/4" to 2" pipe straight from each individual rotor. The collector should be in the 2 1/2" area for street if collected in a short primary and some long primary systems and 2 1/2" collector to an expansion to 3" if a higher powerband long primary is used in certain applications. This is on a 2 rotor. A 3 rotor gets larger after the collector. This is what I've deduced after a whole lot of experimentation just to see what works. 2 1/4" after the collector is still a little small but does work fine. It is still bigger than the stock 2" but not quite optimum. These figures are what I have found to work on street cars. Race cars are a little different due to powerband requirements.
You have dealt with scavenging and pressure waves but you haven't completely covered all the bases. I'm sure you know all of this though and just forgot to type it out. There are two kinds of waves that travel through the exhaust (and intake as well). First there is the gas pressure wave. This is the big scavenging wave. Length of the pipe, diameter, collector point and size all affect this. This is tuned by utilizing the exhaust gasses themselves and how they interact with the others from the other rotors or cylinders. On a rotary depending on how extreme the porting style is these can stay completely seperate or collect at any of a number of locations. The more port overlap between intake and exhaust however, the more important it is to collect these. On a high overlap engine, backpressure is your enemy. The more free the flow the better but only if it is scavenged. This doesn't mean do not put any exhaust on the car. On a high overlap engine it is extremely critical that the system be collected. This will help scavenge the corresponding tube or tubes since there is a constant pulling from the other side. As long as the muffler (if there is one) or anything else in the exhaust system flow good enough the constant flow (when tuned properly) will actually help pull the gasses out of the other side of the engine. This scavenging is making the system less restrictive than no exhaust at all. Don't get scavenging confused with back pressure. Back pressure can aid in low end power in a big way but it is possible to have less pressure in the exhaust from the engines point of view than no exhaust at all. The second type of waves are purely acoustical. These are what we try to utilize in the intake manifold since the intake runners are really too short for inertial charging. Back to the exhaust though. Acoustic waves travel back and forth at the speed of sound. These sound waves are also a form of pressure wave. Depending on how long the exhaust is these wave can arrive back at the exhaust port as either a high pressure or low pressure wave and they will in both cases depending on the rpm and tuning. If the high pressure part of the wave arrives while the port is open then it is a small hinderence. However, if and when it arrives in the form of the low pressure part of the sound wave then it is a gain. You can either try to develop a system that utilizes gas pressure waves and acoustic waves at the same point in the rpm range but it is more likely that the system will have these benefits at two different spots in the powerband. The acoustic scavenging is a much smaller effect so it is generally the gas pressure waves we tune around for exhaust use. Intakes are tuned around similar methods but are more focused on the acoustic side of it but thats info for a different thread.
You have dealt with scavenging and pressure waves but you haven't completely covered all the bases. I'm sure you know all of this though and just forgot to type it out. There are two kinds of waves that travel through the exhaust (and intake as well). First there is the gas pressure wave. This is the big scavenging wave. Length of the pipe, diameter, collector point and size all affect this. This is tuned by utilizing the exhaust gasses themselves and how they interact with the others from the other rotors or cylinders. On a rotary depending on how extreme the porting style is these can stay completely seperate or collect at any of a number of locations. The more port overlap between intake and exhaust however, the more important it is to collect these. On a high overlap engine, backpressure is your enemy. The more free the flow the better but only if it is scavenged. This doesn't mean do not put any exhaust on the car. On a high overlap engine it is extremely critical that the system be collected. This will help scavenge the corresponding tube or tubes since there is a constant pulling from the other side. As long as the muffler (if there is one) or anything else in the exhaust system flow good enough the constant flow (when tuned properly) will actually help pull the gasses out of the other side of the engine. This scavenging is making the system less restrictive than no exhaust at all. Don't get scavenging confused with back pressure. Back pressure can aid in low end power in a big way but it is possible to have less pressure in the exhaust from the engines point of view than no exhaust at all. The second type of waves are purely acoustical. These are what we try to utilize in the intake manifold since the intake runners are really too short for inertial charging. Back to the exhaust though. Acoustic waves travel back and forth at the speed of sound. These sound waves are also a form of pressure wave. Depending on how long the exhaust is these wave can arrive back at the exhaust port as either a high pressure or low pressure wave and they will in both cases depending on the rpm and tuning. If the high pressure part of the wave arrives while the port is open then it is a small hinderence. However, if and when it arrives in the form of the low pressure part of the sound wave then it is a gain. You can either try to develop a system that utilizes gas pressure waves and acoustic waves at the same point in the rpm range but it is more likely that the system will have these benefits at two different spots in the powerband. The acoustic scavenging is a much smaller effect so it is generally the gas pressure waves we tune around for exhaust use. Intakes are tuned around similar methods but are more focused on the acoustic side of it but thats info for a different thread.
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05-16-03, 05:06 PM
#8
...94% correct.
Thread Starter
damn...lol...where were you when I was initially putting this write-up together? You're correct in your assessment that the tubing sizes I listed were a tad smaller than most people would really consider...a 13B, if intended to spend the majority of its life, should hang around 2.5" or possibly 2.75" but this diminishes the streetabillity of the car. The dimensions I gave were in an attempt to specify what sizes would be best to keep the low-end in a usable range. But, most of this stuff is slightly inaccurate, as it's hard to give the specifics for each individual vehicle. I appreciate you pointing it out to me and other readers.
05-16-03, 05:07 PM
#9
...94% correct.
Thread Starter
Originally posted by drago86
free exhaust
15.7 quarter and a top speed of 147mph <-- isnt that trap speed a tad high for a 15.7?
free exhaust
15.7 quarter and a top speed of 147mph <-- isnt that trap speed a tad high for a 15.7?
05-16-03, 06:14 PM
#10
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I am just wondering can anyone explain if it is better to have a collected exhaust on a side exit system or a true dual exhaust with a side exit system. The reson for asking this is because I have ordered the mufflers for my cars side exit exhaust that I am going to build, and I want to know wich would give me better power for what.
05-17-03, 01:56 PM
#12
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If we are talking about exhuast I figured I would post up these two articles as they have lots of good information.
http://personal.riverusers.com/~yawpower/jantech.html
http://personal.riverusers.com/~yawpower/febtech.html
And I woudl like it if anyone could find a more "in-depth" article on pressure wave tuning in both the exhaust and the intake.
Thanks
http://personal.riverusers.com/~yawpower/jantech.html
http://personal.riverusers.com/~yawpower/febtech.html
And I woudl like it if anyone could find a more "in-depth" article on pressure wave tuning in both the exhaust and the intake.
Thanks
05-19-03, 05:17 PM
#14
Lots of my knowledge of intakes and exhausts came from phone and e-mail conversations with Paul Yaw several years ago. He probably has no clue who I am now. He is absolutely against uncollected systems on rotaries (unless his view has changed since then). He is extraordinarily knowledgeable when it comes to everything rotary. He is the person who I learned about doing new exhaust sleeves from. He is also the person who did the flowbench testing on 6 port sleeves and showed that a radius will only add a 1% increase in airflow on systems that still use the sleeves. He's too smart for his own good. All of my experimentation has revolved around the things I learned from him years ago. Volume means nothing without velocity. His words of wisdom.
Corey: I would collect it as far back as possible in your setup. You can dual it out but it will be louder and you may not like your powerband. I've never done a true dual this short before so I can't say that it does or doesn't work.
I am working on a different form of system right now on my GSL-SE. It is a little unorthodox on rotaries but I'm big into wasting money for knowledge sake. It is going to use an X-pipe from Dr. Gas. However this isn't just a plain straight X pipe like it would be if you just joined 2 merge collectors together end to end. I am going to try a tangentially siamesed X-pipe. Here's the reason. On a true dual system you get good low end power but start to suffer on the top end due to lack of gas pressure wave scavenging. It gets even worse on big port styles. On a collected system you get much better top end from scavenging and depending on where you put the collector you can have a higher or lower power peak. Low end can be good with a collected system if the collector is far enough back but an uncollected system generally has better low end. The goal of my system is to try to get some of the benefits of each system so the powerband will be the most useful for street use. A tangentially siamesed system does scavenge but not all of the gasses go to the other side. It is my hope that low end and top end will be a nice compromise between a good collected system and a true dual. The sound should be unique as well sounding like a combination of the two. We shall see. I might hate it, it might not work, it might sound bad, who knows. Then again it might work great. We'll see.
Corey: I would collect it as far back as possible in your setup. You can dual it out but it will be louder and you may not like your powerband. I've never done a true dual this short before so I can't say that it does or doesn't work.
I am working on a different form of system right now on my GSL-SE. It is a little unorthodox on rotaries but I'm big into wasting money for knowledge sake. It is going to use an X-pipe from Dr. Gas. However this isn't just a plain straight X pipe like it would be if you just joined 2 merge collectors together end to end. I am going to try a tangentially siamesed X-pipe. Here's the reason. On a true dual system you get good low end power but start to suffer on the top end due to lack of gas pressure wave scavenging. It gets even worse on big port styles. On a collected system you get much better top end from scavenging and depending on where you put the collector you can have a higher or lower power peak. Low end can be good with a collected system if the collector is far enough back but an uncollected system generally has better low end. The goal of my system is to try to get some of the benefits of each system so the powerband will be the most useful for street use. A tangentially siamesed system does scavenge but not all of the gasses go to the other side. It is my hope that low end and top end will be a nice compromise between a good collected system and a true dual. The sound should be unique as well sounding like a combination of the two. We shall see. I might hate it, it might not work, it might sound bad, who knows. Then again it might work great. We'll see.
05-19-03, 05:43 PM
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It seems like if I used two mufflers on a true dual that it would be quiter than if I used just one on a collected. Well since I have ordered two mufflers I will go with a true dual. But latter on I will make a collector and see if it is better, but I guess that would be a matter of opinion and use. Anyways I will try to get around to trying both.
05-20-03, 12:12 PM
#17
Cory: You may be pleasantly surprised at how loud an uncollected system is in relation to a collected system, even using the same mufflers. The mixing of pulses from both sides of the engine also serve to help quiet (reduce decibal level) the exhaust. Not saying by any means though that it makes it quiet. Just a little less loud.
Makenzie71: Here's some more info for you.
This next part will get long so grab a refeshment and use the restroom before reading.
Here are some basic guidelines for getting good power out of you exhaust. First of all, name brands mean nothing!!! I don't care if its made by Greddy, Dynomax, HKS, or anyone else. If its a crap design or a good design will not be affected by who's name is stamped on it. We'll start with the muffler since this is the first thing people usually replace. Get a straight through design. There are 2 types of straight through designs and only one of them is good. The first design is the perforated core. This is a tube that has many small holes in it around the periphery of the tube which are lined on the opposite side by either fiberglass or stainless steel. Most are fiberglass and hold up very well even on rotaries provided that they are on the back of the car and are not being used as pre-silencers. The stainless steel packing is always more durable but also more expensive. The second type is the louvered core. This design is junk pure and simple. Unfortunately this is what most of the import crowd like to install on their cars. The louvered cores have small dimples that extend into the airstream and catch some of the air and direct it into the packing material. These louvers effectively reduce the usable pipe size through the muffler as well as creating huge ammounts of turbulence and backpressure regardless of their straight through design. They are also not terribly effective when it comes to muffling ability. If these mufflers are turned around backwards then their flow is improved but they still suck so just avoid them. On a funnier yet more pathetic note many of these mufflers are too loud and come with a restrictor that inserts into the end of the muffler to help quiet it down. It is argued by the manufacturers that these can be inserted to be quiet for street driving but then removed for racing. Basically you either have a loud poorly flowing muffler, or a slightly quieter, even worse flow POS under your car. Whats the point? Other muffler styles include chambered designs such as the factory units and those from Flowmaster. I like to call the Flowmasters 'redneck' mufflers. Yes they flow better than stock. No chambered design will ever flow as much as a straight through design and their effectiveness at sound reduction is directly proportional to their restrictiveness. On a rotary they will disintegrate over time from excess heat. Then we have the 'turbo' style mufflers. Avoid these at all costs. Too much turbulence and restriction. The Dynomax Superturbo series adds a u shaped insert to aid in flow and these work better than all the other turbo designs. I would consider only this turbo style muffler to be acceptable as only a direct replacement for a factory muffler. Supertraps are next. These mufflers use discs which depending on how many are used allow on for a certain amount of gas and therefore noise to exit the car. I don't care who says what about them, they suck. They are only just acceptable if they are completely uncapped but then they aren't mufflers anymore. The last design is the entropy muffler. This is a relatively new and unique style of muffler fom Spintech. These have to be seen to be comprehended but they can't burn out and are made from stainless steel. Due to their design they get more efficient as the flow increases!!! Check them out at www.spintechmufflers.com I like these!!!
That covers mufflers. Long wasn't it?! There are a couple of other muffler designs out there but I don't consider them significant enough to mention as viable alternatives.
The rest of the exhaust system should be restriction free. Use good mandrel bent pipes. Do not use the muffler shop type of bends or the crimped bends. Terrible for airflow. If you are upgrading a factory catback system, what is the point of going with a larger diameter system if your header and cat are smaller? I see so many people do this. Keep it consistent and design around your needs. It is relatively cheap to fab up your own design around your own needs and it will probably just work as good as any store bought system if not better in some cases. I'm dissappointed if I pay more than about $300 for a complete system. Sure I could chrome plate it or polish it or put a logo on it but it is under the car where I can't see it and it gets dirty so why waste the money? Other aspects of exhaust design I'l have to cover at a later time. I just got sick of typing.
Makenzie71: Here's some more info for you.
This next part will get long so grab a refeshment and use the restroom before reading.
Here are some basic guidelines for getting good power out of you exhaust. First of all, name brands mean nothing!!! I don't care if its made by Greddy, Dynomax, HKS, or anyone else. If its a crap design or a good design will not be affected by who's name is stamped on it. We'll start with the muffler since this is the first thing people usually replace. Get a straight through design. There are 2 types of straight through designs and only one of them is good. The first design is the perforated core. This is a tube that has many small holes in it around the periphery of the tube which are lined on the opposite side by either fiberglass or stainless steel. Most are fiberglass and hold up very well even on rotaries provided that they are on the back of the car and are not being used as pre-silencers. The stainless steel packing is always more durable but also more expensive. The second type is the louvered core. This design is junk pure and simple. Unfortunately this is what most of the import crowd like to install on their cars. The louvered cores have small dimples that extend into the airstream and catch some of the air and direct it into the packing material. These louvers effectively reduce the usable pipe size through the muffler as well as creating huge ammounts of turbulence and backpressure regardless of their straight through design. They are also not terribly effective when it comes to muffling ability. If these mufflers are turned around backwards then their flow is improved but they still suck so just avoid them. On a funnier yet more pathetic note many of these mufflers are too loud and come with a restrictor that inserts into the end of the muffler to help quiet it down. It is argued by the manufacturers that these can be inserted to be quiet for street driving but then removed for racing. Basically you either have a loud poorly flowing muffler, or a slightly quieter, even worse flow POS under your car. Whats the point? Other muffler styles include chambered designs such as the factory units and those from Flowmaster. I like to call the Flowmasters 'redneck' mufflers. Yes they flow better than stock. No chambered design will ever flow as much as a straight through design and their effectiveness at sound reduction is directly proportional to their restrictiveness. On a rotary they will disintegrate over time from excess heat. Then we have the 'turbo' style mufflers. Avoid these at all costs. Too much turbulence and restriction. The Dynomax Superturbo series adds a u shaped insert to aid in flow and these work better than all the other turbo designs. I would consider only this turbo style muffler to be acceptable as only a direct replacement for a factory muffler. Supertraps are next. These mufflers use discs which depending on how many are used allow on for a certain amount of gas and therefore noise to exit the car. I don't care who says what about them, they suck. They are only just acceptable if they are completely uncapped but then they aren't mufflers anymore. The last design is the entropy muffler. This is a relatively new and unique style of muffler fom Spintech. These have to be seen to be comprehended but they can't burn out and are made from stainless steel. Due to their design they get more efficient as the flow increases!!! Check them out at www.spintechmufflers.com I like these!!!
That covers mufflers. Long wasn't it?! There are a couple of other muffler designs out there but I don't consider them significant enough to mention as viable alternatives.
The rest of the exhaust system should be restriction free. Use good mandrel bent pipes. Do not use the muffler shop type of bends or the crimped bends. Terrible for airflow. If you are upgrading a factory catback system, what is the point of going with a larger diameter system if your header and cat are smaller? I see so many people do this. Keep it consistent and design around your needs. It is relatively cheap to fab up your own design around your own needs and it will probably just work as good as any store bought system if not better in some cases. I'm dissappointed if I pay more than about $300 for a complete system. Sure I could chrome plate it or polish it or put a logo on it but it is under the car where I can't see it and it gets dirty so why waste the money? Other aspects of exhaust design I'l have to cover at a later time. I just got sick of typing.
Last edited by rotarygod; 05-20-03 at 12:19 PM.
05-20-03, 02:46 PM
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This is a relatively new and unique style of muffler fom Spintech. These have to be seen to be comprehended but they can't burn out and are made from stainless steel. Due to their design they get more efficient as the flow increases!!! Check them out at www.spintechmufflers.com I like these!!!
Sweet, I bought a set of shoot out style mufflers with 2 in inlet and 2 in outlet, modle # 6111 from them, but it is a pain in the but because you have to send them money and then wait for them to send you the mufflers, and that is what I had to do because I don't have a credit card. But they should be at my door step in about a week or so, I am hopeing it won't take any longer than that.
05-20-03, 03:03 PM
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Yeah it will be a bitch won't it, Ohh well I'll just make sure the old people are awake and take it for a spin at about midnight for the first time when I get them put on. Do you think that I could pack them with steel wool, to quit them down if they are to loud even for me??? As long as it sounds better than the Aero Speed mufflers that are on my car now I will be happy, wether it is loud or not.
05-20-03, 03:32 PM
#21
Nope you can't really modify those mufflers. they are so simple it's going to be hard to do anything to them. If you add packing it will probably still be loud, sound bad, and it probably won't won't near as good anymore either.
Just to reiterate...They are going to be REALLY F&*CKING LOUD!!!!!!
Just to reiterate...They are going to be REALLY F&*CKING LOUD!!!!!!
05-23-03, 11:34 AM
#24
Here are a couple of links which will really get your mind going. They are very informative and scientific. The first link is just a small basic theory behind headers.
http://www.burnsstainless.com/TechAr...ry/theory.html
The next link is actually to an aircraft site. Regardless it has some very useful articles which applies to all engines in general. These are extremely informative and should probably be printed out and read since the Adobe Acrobat fomat gets very annoying. They explain very well the differences in acoustic and pressure wave tuning. There are two articles on exhausts in this link. The first is titled "The EPG and Aircraft Exhaust Systems" and the second is "Aircraft Exhaust Systems IV". There are also a couple of good articles on ignition systems and how they work internally on the engine. There's even an article on the drag coefficient effects of a good wax job on your paint! Check this site out. Your brain will pop.
http://www.cafefoundation.org/research.htm
http://www.burnsstainless.com/TechAr...ry/theory.html
The next link is actually to an aircraft site. Regardless it has some very useful articles which applies to all engines in general. These are extremely informative and should probably be printed out and read since the Adobe Acrobat fomat gets very annoying. They explain very well the differences in acoustic and pressure wave tuning. There are two articles on exhausts in this link. The first is titled "The EPG and Aircraft Exhaust Systems" and the second is "Aircraft Exhaust Systems IV". There are also a couple of good articles on ignition systems and how they work internally on the engine. There's even an article on the drag coefficient effects of a good wax job on your paint! Check this site out. Your brain will pop.
http://www.cafefoundation.org/research.htm