Informative: Exhaust Tuning, what part of the system actually tunes
01-20-10 | 01:45 PM
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From: Houston
Informative: Exhaust Tuning, what part of the system actually tunes
It has been a very long time since I've written anything technical but a recent PM made me realize there is still more to exhaust science that people don't understand. In the past (way past!) I've written lengthy threads on intake and exhaust tuning and now it's time to add an update. First off, for those still referencing the old thread on how to figure intake runner length, throw it away. Forget you ever saw it. While most is correct there is still a fundamental error in that thread which throws the results off pretty far. While I'm not going to explain everything all over again right now, I am going to address one misunderstood concept of exhaust design and that is which part is most important for tuning.
An exhaust needs to be thought of as a system and the whole system affects tuning. This is why I laugh at the latest and greatest header that others drool over and claim is better than the next. You have a few areas that affect tuning but each in their own way. The primary pipes from the header itself are less than half of the tuning potential of any system. How much more power can any good header design really offer than another good design? Not much. Having good results with a nice header on one system may give results that are totally different on another car that has a different exhaust system after the header. Most don't understand why.
Let's start at the header and work our way back. You have the header primary runner length and diameter which you know. We also know that the fewer the bends, and the more gentle they are when we need them, the better. We have also learned that at least 3" is needed after the engine in straight length so as to smooth airflow out of the exhaust ports before they need to hit the first turn. For most people, all of their effort lies in this small part of the exhaust. Let's move back farther.
The collector itself also plays a role in the tuning. How large is the total area? Is there a divergent cone (megaphone) on the collector? How long is it? What is the converging angle of the pipes? Incidentally there is no one right answer for this as pipes that converge at 30 degrees may be perfect for a low rpm but they may work best at 20 degrees at a higher rpm. We can only compromise here as the optimal angle will change depending on rpm and load but it is an important part when it comes to tuning. It is also one of the most often overlooked. Just collecting the pipes together isn't good enough. It's how they do that plays a big role.
Moving on, after the collector we have what we will call the "tailpipe". This is the total system from here on back as perceived by the engine so don't think this is only the muffler tips. The tailpipe ends at the point that the exhaust system suddenly hits a much larger volume such as the entire Earth's atmosphere. We can simulate this termination with an exhaust box though which effectively means the exhaust "ends" at the box. What happens after the box is irrelevant as long as there is enough flow. Tuning from that point back is no longer an issue.
Attention span break: Incidentally on the intake side of things, a plenum chamber represents the beginning of the intake. It is backwards. What comes before the plenum or how long it is, is completely irrelevant to tuning so long as it can flow the required amount of air. If there is no plenum such as with the Renesis intake, everything after the air filter affects tuning. This is why those engines sometimes have idle issues from a simple air filter change. They have changed intake tuning.
Ok, where were we? Ah yes, the termination of the exhaust tailpipe. Wherever we have a large area size, our exhaust system effectively ends. Much like the plenum on the intake side, once this large area is hit on the exhaust, whether it is an exhaust box (exhaust plenum?) or the atmosphere, the exhaust is effectively terminated. Anything you add after this point only needs to flow the required amount of air as tuning no longer has any effect.
Example time: Lets say we have a common system for the 2nd gen. Let's use a full Racing Beat system. We have a Racing Beat header, no cat, a y-pipe, and 2 Power Pulse mufflers. The end of the tuned length is the muffler tips at the back of the car. This is the first large area change in the system. Everything in here plays a role from the header to the mid pipe, to the y-pipe, to the mufflers. Changing any of these will result in some form of tuning change.
Let's say we changed only the mufflers out to some Flowmasters. Not that I'd condone that! These are chambered as opposed to absorptive and do a pretty good job of disappearing as opposed to straight through designs which are effectively the same as adding a length of pipe to the system. The reason is that these mufflers are a large area increase internally which does a pretty good job of simulating an exhaust box which makes the system see them as a termination. With the flowmaters, the end of the tuned length of the exhaust system is the beginning of the mufflers. We have effectively shortened the length of our exhaust. Some people that claim they get a power increase with Flowmasters aren't realizing that not everything has to do with how well it flows. If both types of mufflers flow what the engine needs, neither makes more power than the other as a result. However due a tuning change in the system, one is perceived. If you merely moved a Flowmaster from the rear of the car to the middle of the exhaust system, then you've really shortened up your exhaust! Things are not always as they appear to be. It is only about flow until you don't need anymore. After that, it's all a waste. Muffler B may flow more than Muffler A but if both flow more than the engine needs, neither is better. Don't get caught up in knowing only static flow. Know how it applies to your needs. That's all that matters.
Now lets get to the ultimate custom designed system. No I'm not telling you how to do it. This is an example. Let's say we went all out and designed the ultimate system. We start with a header. We figure out the perfect runner length and diameter through lots of trial and error and ringing ears as we haven't used a muffler to this point! Then we test many different collectors and collector angles to see if the powerband is strengthened where we want it. Then we work our way back to the tailpipe. We try different lengths and suddenly we find that we like a setup that is 30" long after the collector. If we go longer, our powerband becomes undesireable and if we shorten it the same thing happens. This is our sweet spot for this example system. However we are under the car and need the exhaust to go through mufflers and out the back. There are these two problems. Actually it's no problem! In comes the exhaust box. We just add a large hollow chamber mid car 30" after the collector and suddenly the exhaust thinks it has hit the atmosphere. The exhaust tuning terminates at the entrance to the box. If the box is not of sufficient size, what happens after it may be partially visible to the system. Now with our exhaust tuning terminated, all we need to do now is choose a muffler system that can flow what we need it to. Nothing else matters. You can put some very quiet mufflers on. As long as they hit the flow requirements, your power won't change. If they are restrictive, power will suffer. Remember you only need what you need and no more. More is not better and sometimes it's worse!
Now let's talk about pure header designs and why none truly impress me. It's not to say I don't think there are better ones out there than others. There absolutely are. However how were those headers designed? Did someone pick out 304 stainless as a material and basically say they were going to use a 3" straight out of the motor before turning gently and then collect with true equal length pipes to a smooth collector and tig weld it all together? That's nice and all but where does the tuning come into play? Keep in mind that unless you have a true equal length intake manifold with all equal length runners, you do NOT want an equal length header! Suddenly many of these so called "best headers" don't sound all that impressive. There is far more involved in exhaust tuning than making it pretty and all equal length.
Was this header designed on a dyno or in a real car? What kind of exhaust system did that setup use? What kind of mufflers? How many? How long was the total system? You should know that from reading the above that everything in the system up to the point of a large area increase affects tuning. That header may have been designed to get the most power on that setup at the rpm they wanted it at but that was with everything they had it attached to. Whose to say that playing with the exhaust after this point and completely redesigning the header wouldn't have given them even more power where they wanted it? No one knows but in most cases it would probably be true. The header is less than half (closer to a 3rd) of the total system tuning so putting all of your effort into only it is completely missing most of the story. It is an important part but of equally important other parts that only work together perfectly as an entire system.
Impressed by polished stainless, 3" straights before the first turn, gentle curves, and equal lengths, you buy this header and install it on your car. You are less than impressed. Why? It's the best header made for the RX-7! The fact that you have Walmart mufflers and a half rusted y-pipe don't register as it's supposed to be the header that made all that power. Nope. Only some of it. If you want their results, you need to exactly copy them and I mean exactly.
So what header would impress me you say? None. I want to see an exhaust system that is designed in a way that it is tunable to each individual car and powerband. I want it to have the ability to be quiet if desired or loud if desired with no effect on power either way. I want a system that is great for the street but with a few minutes of work can be retuned for a track or a different climate. Think it can't be done? It can and it will fit under your car. Nothing complex. No fancy electronics. No butterfly valves. Just a smart design. Study the concepts above and start thinking past the header. That's where the secret is.
If you see a header come out, and the company/seller/individual pushing it claims it to be the best out there, and it doesn't involve the rest of the exhaust system, the only thing they've really done is shown their true knowledge level when it comes to exhaust design and apparently it's less than 50% of what they should know!
The responses to this should get interesting pretty fast!
An exhaust needs to be thought of as a system and the whole system affects tuning. This is why I laugh at the latest and greatest header that others drool over and claim is better than the next. You have a few areas that affect tuning but each in their own way. The primary pipes from the header itself are less than half of the tuning potential of any system. How much more power can any good header design really offer than another good design? Not much. Having good results with a nice header on one system may give results that are totally different on another car that has a different exhaust system after the header. Most don't understand why.
Let's start at the header and work our way back. You have the header primary runner length and diameter which you know. We also know that the fewer the bends, and the more gentle they are when we need them, the better. We have also learned that at least 3" is needed after the engine in straight length so as to smooth airflow out of the exhaust ports before they need to hit the first turn. For most people, all of their effort lies in this small part of the exhaust. Let's move back farther.
The collector itself also plays a role in the tuning. How large is the total area? Is there a divergent cone (megaphone) on the collector? How long is it? What is the converging angle of the pipes? Incidentally there is no one right answer for this as pipes that converge at 30 degrees may be perfect for a low rpm but they may work best at 20 degrees at a higher rpm. We can only compromise here as the optimal angle will change depending on rpm and load but it is an important part when it comes to tuning. It is also one of the most often overlooked. Just collecting the pipes together isn't good enough. It's how they do that plays a big role.
Moving on, after the collector we have what we will call the "tailpipe". This is the total system from here on back as perceived by the engine so don't think this is only the muffler tips. The tailpipe ends at the point that the exhaust system suddenly hits a much larger volume such as the entire Earth's atmosphere. We can simulate this termination with an exhaust box though which effectively means the exhaust "ends" at the box. What happens after the box is irrelevant as long as there is enough flow. Tuning from that point back is no longer an issue.
Attention span break: Incidentally on the intake side of things, a plenum chamber represents the beginning of the intake. It is backwards. What comes before the plenum or how long it is, is completely irrelevant to tuning so long as it can flow the required amount of air. If there is no plenum such as with the Renesis intake, everything after the air filter affects tuning. This is why those engines sometimes have idle issues from a simple air filter change. They have changed intake tuning.
Ok, where were we? Ah yes, the termination of the exhaust tailpipe. Wherever we have a large area size, our exhaust system effectively ends. Much like the plenum on the intake side, once this large area is hit on the exhaust, whether it is an exhaust box (exhaust plenum?) or the atmosphere, the exhaust is effectively terminated. Anything you add after this point only needs to flow the required amount of air as tuning no longer has any effect.
Example time: Lets say we have a common system for the 2nd gen. Let's use a full Racing Beat system. We have a Racing Beat header, no cat, a y-pipe, and 2 Power Pulse mufflers. The end of the tuned length is the muffler tips at the back of the car. This is the first large area change in the system. Everything in here plays a role from the header to the mid pipe, to the y-pipe, to the mufflers. Changing any of these will result in some form of tuning change.
Let's say we changed only the mufflers out to some Flowmasters. Not that I'd condone that! These are chambered as opposed to absorptive and do a pretty good job of disappearing as opposed to straight through designs which are effectively the same as adding a length of pipe to the system. The reason is that these mufflers are a large area increase internally which does a pretty good job of simulating an exhaust box which makes the system see them as a termination. With the flowmaters, the end of the tuned length of the exhaust system is the beginning of the mufflers. We have effectively shortened the length of our exhaust. Some people that claim they get a power increase with Flowmasters aren't realizing that not everything has to do with how well it flows. If both types of mufflers flow what the engine needs, neither makes more power than the other as a result. However due a tuning change in the system, one is perceived. If you merely moved a Flowmaster from the rear of the car to the middle of the exhaust system, then you've really shortened up your exhaust! Things are not always as they appear to be. It is only about flow until you don't need anymore. After that, it's all a waste. Muffler B may flow more than Muffler A but if both flow more than the engine needs, neither is better. Don't get caught up in knowing only static flow. Know how it applies to your needs. That's all that matters.
Now lets get to the ultimate custom designed system. No I'm not telling you how to do it. This is an example. Let's say we went all out and designed the ultimate system. We start with a header. We figure out the perfect runner length and diameter through lots of trial and error and ringing ears as we haven't used a muffler to this point! Then we test many different collectors and collector angles to see if the powerband is strengthened where we want it. Then we work our way back to the tailpipe. We try different lengths and suddenly we find that we like a setup that is 30" long after the collector. If we go longer, our powerband becomes undesireable and if we shorten it the same thing happens. This is our sweet spot for this example system. However we are under the car and need the exhaust to go through mufflers and out the back. There are these two problems. Actually it's no problem! In comes the exhaust box. We just add a large hollow chamber mid car 30" after the collector and suddenly the exhaust thinks it has hit the atmosphere. The exhaust tuning terminates at the entrance to the box. If the box is not of sufficient size, what happens after it may be partially visible to the system. Now with our exhaust tuning terminated, all we need to do now is choose a muffler system that can flow what we need it to. Nothing else matters. You can put some very quiet mufflers on. As long as they hit the flow requirements, your power won't change. If they are restrictive, power will suffer. Remember you only need what you need and no more. More is not better and sometimes it's worse!
Now let's talk about pure header designs and why none truly impress me. It's not to say I don't think there are better ones out there than others. There absolutely are. However how were those headers designed? Did someone pick out 304 stainless as a material and basically say they were going to use a 3" straight out of the motor before turning gently and then collect with true equal length pipes to a smooth collector and tig weld it all together? That's nice and all but where does the tuning come into play? Keep in mind that unless you have a true equal length intake manifold with all equal length runners, you do NOT want an equal length header! Suddenly many of these so called "best headers" don't sound all that impressive. There is far more involved in exhaust tuning than making it pretty and all equal length.
Was this header designed on a dyno or in a real car? What kind of exhaust system did that setup use? What kind of mufflers? How many? How long was the total system? You should know that from reading the above that everything in the system up to the point of a large area increase affects tuning. That header may have been designed to get the most power on that setup at the rpm they wanted it at but that was with everything they had it attached to. Whose to say that playing with the exhaust after this point and completely redesigning the header wouldn't have given them even more power where they wanted it? No one knows but in most cases it would probably be true. The header is less than half (closer to a 3rd) of the total system tuning so putting all of your effort into only it is completely missing most of the story. It is an important part but of equally important other parts that only work together perfectly as an entire system.
Impressed by polished stainless, 3" straights before the first turn, gentle curves, and equal lengths, you buy this header and install it on your car. You are less than impressed. Why? It's the best header made for the RX-7! The fact that you have Walmart mufflers and a half rusted y-pipe don't register as it's supposed to be the header that made all that power. Nope. Only some of it. If you want their results, you need to exactly copy them and I mean exactly.
So what header would impress me you say? None. I want to see an exhaust system that is designed in a way that it is tunable to each individual car and powerband. I want it to have the ability to be quiet if desired or loud if desired with no effect on power either way. I want a system that is great for the street but with a few minutes of work can be retuned for a track or a different climate. Think it can't be done? It can and it will fit under your car. Nothing complex. No fancy electronics. No butterfly valves. Just a smart design. Study the concepts above and start thinking past the header. That's where the secret is.
If you see a header come out, and the company/seller/individual pushing it claims it to be the best out there, and it doesn't involve the rest of the exhaust system, the only thing they've really done is shown their true knowledge level when it comes to exhaust design and apparently it's less than 50% of what they should know!
The responses to this should get interesting pretty fast!
01-20-10 | 02:33 PM
#2
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From: https://www2.mazda.com/en/100th/
i agree!
looking over tons of posts, links and as many books as i could find, i found that header primary length was pretty well known, collector diameter was pretty well known.
but
things like the total tuned length of the system arent.
and
you find this amazing variety of exhausts that work, from mazdatrix's really long setup, to logans 2.5", to the true dual setup everyone around here with a BP/PP runs
the goal of course is to have something streetably quiet, AND power
looking over tons of posts, links and as many books as i could find, i found that header primary length was pretty well known, collector diameter was pretty well known.
but
things like the total tuned length of the system arent.
and
you find this amazing variety of exhausts that work, from mazdatrix's really long setup, to logans 2.5", to the true dual setup everyone around here with a BP/PP runs
the goal of course is to have something streetably quiet, AND power
01-20-10 | 02:43 PM
#3
Excellent article. Moderators archive at once!
Since most carb intakes have to deal with the tilt of the engine to keep
the bowls fuel level, then the intakes are by definition unequal. So this
means that the corresponding tunable length needs to be proportionally
unequal as well. Correct?
I know cooling issues cause some of the issues with uneven EGTs
in the front vesus rear rotors but maybe this is also a cause as well. It
also explains why on my Dell the rear rotors idle jet has to be set slighlty
differently when its all tuned.
Since most carb intakes have to deal with the tilt of the engine to keep
the bowls fuel level, then the intakes are by definition unequal. So this
means that the corresponding tunable length needs to be proportionally
unequal as well. Correct?
I know cooling issues cause some of the issues with uneven EGTs
in the front vesus rear rotors but maybe this is also a cause as well. It
also explains why on my Dell the rear rotors idle jet has to be set slighlty
differently when its all tuned.
01-20-10 | 05:09 PM
#5
Awesome stuff. It helps a lot to have it all explained in that way. I'm not sure you will get too many nay-sayers, since your logic is very sound, it was well explained, and your avatar stares creepily at anyone who dares to disagree with the rotarygod!
Anyhow, about your post; after coming up with an appropriate header, collector, etc.; It would be pretty cool to have several short sections of exhaust tubing, in a straight section of the pipe after the header, all flanged, as well as a muffler that can act as an expansion chamber, or system termination, or whatever one chooses to call it...
Then you could move the expansion chamber muffler thingy closer or further from the header by removing the flanged tubes and re-positioning them in front of or behind the muffler. Then you could observe the changes. Cool.
Ooo! Then you could even put a catalytic converter (given that it flows enough to not cause a change and make the system "see it") after the muffler expansion thingy, so you could reduce the tailpipe stink (although I think some of us are addicted to it...) and reduce noise. And theoretically you would still make as much power as you originally designed it to make.
Anyhow, about your post; after coming up with an appropriate header, collector, etc.; It would be pretty cool to have several short sections of exhaust tubing, in a straight section of the pipe after the header, all flanged, as well as a muffler that can act as an expansion chamber, or system termination, or whatever one chooses to call it...
Then you could move the expansion chamber muffler thingy closer or further from the header by removing the flanged tubes and re-positioning them in front of or behind the muffler. Then you could observe the changes. Cool.
Ooo! Then you could even put a catalytic converter (given that it flows enough to not cause a change and make the system "see it") after the muffler expansion thingy, so you could reduce the tailpipe stink (although I think some of us are addicted to it...) and reduce noise. And theoretically you would still make as much power as you originally designed it to make.
01-20-10 | 05:33 PM
#6
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From: Houston
There are many combinations that work well. The best system isn't going to design every aspect that plays a role to strengthen the powerband all at the same point. This would make things a bit peaky and narrow. The best systems give up a bit here and there in the name of average power. This drives better and is ultimately quicker. If we design our header to tune for 6000 rpm, setup our collector to benefit at 6500 rpm and the tailpipe section to benefit at 7000 rpm, we've got a system that would be easier to drive than one where everything was all tuned for a 7000 rpm bump even though that one may make more absolute power at that spot.
Now lets say we change our exhaust design. We tune the header to 7000, the collector to 6000, and our tailpipe to 6500 rpm. We still get the same basic powerband as the first setup even though everything was different.
Then we get into harmonics but there are literally volumes of books on the subject. This is just a quick example to hopefully help people understand the kinds of things happening in the exhaust system. It should also show that there is no one right way to do things!
I'm going to give you guys a little tip and this is one that will get you thinking. When figuring out exhaust or even intake lengths through mathematical calculations, we obviously have several variables. Change any of them and you change the results. One variable is the speed of sound. This is important because it is temperature dependent. The higher the temperature, the faster the speed of sound. If we change the speed of sound, we change the tuned length. In other words if we change the temperature of the gas, we change the tuned length. See where I'm going yet?
Water injection. But where? Straight in the exhaust right after the exhaust ports. In theory, this is the key, if we change the temperature of the exhaust gasses from let's say for this example from 1600* F to 1500* F, it should also change the exhaust tuning point by moving it down by about 750 rpm or so. By tapering in and out varying amounts of water, you can theoretically have an exhaust that retunes but without the complexity of having any moving parts. To expand this, if we can in fact change exhaust tuning with water, we could also stagger the amounts between pipes to functionally equalize any length inconsistencies between header pipes. In other words, equal length wouldn't necessarily matter as long as we could stagger jet the water. Incidentally on a 12A engine, if you stagger jet each rotor, you can pick up about 2 hp due to tuning differences through the manifold. Now don't expect huge power gains from all of this. You probably won't get them. But more is more. How much is anyones guess though.
Have fun thinking about that one!
Now lets say we change our exhaust design. We tune the header to 7000, the collector to 6000, and our tailpipe to 6500 rpm. We still get the same basic powerband as the first setup even though everything was different.
Then we get into harmonics but there are literally volumes of books on the subject. This is just a quick example to hopefully help people understand the kinds of things happening in the exhaust system. It should also show that there is no one right way to do things!
I'm going to give you guys a little tip and this is one that will get you thinking. When figuring out exhaust or even intake lengths through mathematical calculations, we obviously have several variables. Change any of them and you change the results. One variable is the speed of sound. This is important because it is temperature dependent. The higher the temperature, the faster the speed of sound. If we change the speed of sound, we change the tuned length. In other words if we change the temperature of the gas, we change the tuned length. See where I'm going yet?
Water injection. But where? Straight in the exhaust right after the exhaust ports. In theory, this is the key, if we change the temperature of the exhaust gasses from let's say for this example from 1600* F to 1500* F, it should also change the exhaust tuning point by moving it down by about 750 rpm or so. By tapering in and out varying amounts of water, you can theoretically have an exhaust that retunes but without the complexity of having any moving parts. To expand this, if we can in fact change exhaust tuning with water, we could also stagger the amounts between pipes to functionally equalize any length inconsistencies between header pipes. In other words, equal length wouldn't necessarily matter as long as we could stagger jet the water. Incidentally on a 12A engine, if you stagger jet each rotor, you can pick up about 2 hp due to tuning differences through the manifold. Now don't expect huge power gains from all of this. You probably won't get them. But more is more. How much is anyones guess though.
Have fun thinking about that one!
01-20-10 | 06:13 PM
#7
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we know about how long headers should be, megaphone type collector is good, its everything AFTER that that's the problem.
dynomax is nice because they list the muffers by CFM.
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01-20-10 | 07:57 PM
#8
Anyhow, about your post; after coming up with an appropriate header, collector, etc.; It would be pretty cool to have several short sections of exhaust tubing, in a straight section of the pipe after the header, all flanged, as well as a muffler that can act as an expansion chamber, or system termination, or whatever one chooses to call it...
I used the tank for the cold start *way to small* with a generic washer pump from the HELP section at autozone to tube with a screen at the end right after the flange, so far from optimal but it was just a test. I have to many other things I'm working on *again... damn "redundant" external HDD* but this is on the list to keep playing with.
01-20-10 | 10:17 PM
#9
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From: Houston
The exhaust box is very simple. It's a hollow box! Nothing more complex than that. The larger the better but there is a functional limit on how small you can go and get most of the benefit. I forgot that number so I'll get back to it later.
If you want to design each section of the exhaust system independently but still want hearing and don't mind a little extra work, it can be done. We all know the first aspects of a header. Keep it straight as long as possible and keep the bends as gentle as possible. Worry about getting around the first corner. At this point the length is still fairly short. Try fitting a sort of exhaust box here with each header pipe terminating in it. Then make sure you have a large enough pipe leaving it to not hurt flow and send it through a muffler or wherever you want it. Design the box so that it unbolts from a flange on the header. Basically just use the road race header flange from Racing Beat. You can use another flange and weld in various lengths of pipe that insert between the header pipes and the box, effectively making your header pipes longer. You can try several of these but make sure you have enough depth in the box for the inserts. Not test to see where you want your powerband.
Next once you've figured that out, you want to know your collector. Again build a box that bolts on after or at the collector and swap various ones out using the road race header flanges. Try different converging angles, and pipe areas that they collect to. When you get this where you want it, move the box back and start playing with tailpipe lengths. You see how this all works.
It is a bit intensive for the home mechanic/hobbiest and is easiest on an engine dyno but it can be done with patience and lots of trial and error. If you get real creative you can build the entire system in a way that various designs unbolt and are swappable. Now you've got the ultimate system for any occasion. Just change what you want and go from there. When i see someone build such a system, then I'll be impressed. After you get this far, then you can play with exhaust water injection. Have fun!
If you want to design each section of the exhaust system independently but still want hearing and don't mind a little extra work, it can be done. We all know the first aspects of a header. Keep it straight as long as possible and keep the bends as gentle as possible. Worry about getting around the first corner. At this point the length is still fairly short. Try fitting a sort of exhaust box here with each header pipe terminating in it. Then make sure you have a large enough pipe leaving it to not hurt flow and send it through a muffler or wherever you want it. Design the box so that it unbolts from a flange on the header. Basically just use the road race header flange from Racing Beat. You can use another flange and weld in various lengths of pipe that insert between the header pipes and the box, effectively making your header pipes longer. You can try several of these but make sure you have enough depth in the box for the inserts. Not test to see where you want your powerband.
Next once you've figured that out, you want to know your collector. Again build a box that bolts on after or at the collector and swap various ones out using the road race header flanges. Try different converging angles, and pipe areas that they collect to. When you get this where you want it, move the box back and start playing with tailpipe lengths. You see how this all works.
It is a bit intensive for the home mechanic/hobbiest and is easiest on an engine dyno but it can be done with patience and lots of trial and error. If you get real creative you can build the entire system in a way that various designs unbolt and are swappable. Now you've got the ultimate system for any occasion. Just change what you want and go from there. When i see someone build such a system, then I'll be impressed. After you get this far, then you can play with exhaust water injection. Have fun!
01-21-10 | 02:16 AM
#10
I do have one question about the megaphone. What if instead of having the megaphone directly after the collector, so say there's a 2-3" straight pipe going out and then you megaphone, what would the effects of such a thing be?
Also here's another one to think about, what would happen if you a have 2 different angles of megaphones one after the other. So say you have one that about 2" long running about 8 degree taper, and another one right after that say 1.5" long on a 20 degree taper. Would something like that help you to further broaden your power band?
Another way could also look at thing is a kinda backwards method of the above method. Say you have it originally megaphoned to 4" on the back side instead of say stepping down to 2.5" right away you do a reverse cone going from 4" to 3" and run that for about a foot or so, then step it down again to 2.5".
Just tossing more food for brain I guess.
Lastly what books would you mostly recommend for reading up more on exhaust theories? I would like to get a few and read up.
Also here's another one to think about, what would happen if you a have 2 different angles of megaphones one after the other. So say you have one that about 2" long running about 8 degree taper, and another one right after that say 1.5" long on a 20 degree taper. Would something like that help you to further broaden your power band?
Another way could also look at thing is a kinda backwards method of the above method. Say you have it originally megaphoned to 4" on the back side instead of say stepping down to 2.5" right away you do a reverse cone going from 4" to 3" and run that for about a foot or so, then step it down again to 2.5".
Just tossing more food for brain I guess.
Lastly what books would you mostly recommend for reading up more on exhaust theories? I would like to get a few and read up.
01-21-10 | 11:09 AM
#11
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Joined: Jan 2008
Posts: 232
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From: idaho
if i understand?
my set-up is 26" - 2" primaries w/ 2 90 bend going to 3" 12" long collector
and sence my muffler(open chamber type straight-thru) is 16" from collector that is the end of the system?
that means my system is only 44"s long! on stock ports? where is this going to limit me?
i think you should have posted this 2 weeks ago!
RotaryGod- you alway's have the most interesting topics! THANKS
my set-up is 26" - 2" primaries w/ 2 90 bend going to 3" 12" long collector
and sence my muffler(open chamber type straight-thru) is 16" from collector that is the end of the system?
that means my system is only 44"s long! on stock ports? where is this going to limit me?
i think you should have posted this 2 weeks ago!
RotaryGod- you alway's have the most interesting topics! THANKS
01-21-10 | 11:19 AM
#12
Thread Starter
Rotors still spinning
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From: Houston
A megaphone does have to be directly on the collector itself. There can be a straight piece between them. It will vary it's effect which may be good or bad. The only way to know which is better is to try them. Differing tapers will also have different effects as will their lengths.
An expansion chamber where you have a diverging cone into a larger pipe and then a converging cone back into a smaller pipe also has an effect on power. Typically if designed correctly for your application, it will broaden the powerband a bit at the slight expense of ultimate peak power. This may or may not be desireable.
There are tons of things that play a role in an exhaust and lots of unique things that can be done. You can have dead leg pipes, x-pipes, crossovers, collectors, megaphones, expansion chambers, exhaust boxes, and the list goes on and on. There are lots of ways to do things. In the past I concentrated on trying to learn the math behind it. Now I'm pushing for an understanding of what is actually going on and understanding it. Once you know how certain things play a role, you can start to experiment. If you sit there all day and try to design a system based on math, you are still going to end up with a system that needs to be tweaked and modified to truly do what you want. Here's an example of why.
Let's say we want to calculate a tuned length for a header primary pipe. We go to the trouble to do our math formula and we get a number. Let's say one of our variables, the one for the speed of sound to be exact, was a certain number that basically corresponded to its speed in 1600*F exhaust gas. This formula tells us that we should be tuned to a certain rpm and it's corresponding harmonics. For example in theory we tune for 7000 rpm but the harmonics also tune for 3500 at the 2nd order, 1750 as the 3rd order, etc. You get the idea. However you never see this actually happen because exhaust temps don't remain constant. From the moment that air and fuel get combusted and hit their peak temperature, they immediately start rapidly cooling down. You may have 2000* at the spark plug, 1600* at the exhaust port, and by the time you get out the back of the car through the entire system they may only be 400* or so. You get the idea. When the temperature goes down, the speed of sound changes too and so does tuning.
The speed of sound within the wave length of the first harmonic is going to be faster than the speed of sound through the length of the second harmonic which is more than the 3rd and so forth and so on. What this means is that the return waves do not arrive when we expect them to because all we could do was calculate for fixed variables rather than having a dynamic variable. Suddenly all that math may or may not have been worth it.
The above heat loss issue is compounded by exhaust material. Stainless steel will retain more heat than mild steel will meaning our exhaust gasses will be cooler at the back of the car with the mild steel system than that of the stainless system. This of course applies to other materials too. If we have 2 identical headers but one is stainless and the other is mild steel, they will be tuned completely differently! They may be close but they aren't the same. This makes playing with various designs even more difficult as mild steel is easy to work with an much cheaper. You design a system using mild steel, get it where you want it, and then build it out of stainless only to find it is close but not quite exact in terms of your goals. For street use this really isn't going to be much of an issue but a (good) race team will only prototype with the same material they intend to use for the finished product. A (good) race team will also tune their a/f ratios in the sweet spot of the powerband around egt's. Now you know why. Maintaining a certain egt as long as possible maintains the same tuning for the system as long as possible. If your egt's change too much because you are tuning by a/f ratio only, you may find your powerband falling off a bit in places because of the change in the speed of sound and hence the tuning.
Now don't get all frustrated and scared now that I've said all of this. Many people want all the information they can get on anything that can have any effect at all. Even if it is a small one. It isn't that hard to design a good system for the street. They key is not to get too overwhelmed on the smallest of details that a good race team would focus on. They need that last 1/10th of a horsepower and will go a long way to get it. The first 90% of your power comes with only 10% of the effort. The last 10% of your total power potential takes 90% of your effort. If we only have about 20 more hp to really extract from teh engine, it's not hard to get about 18 of them. Don't ask where I got only 20 more hp from the system though. I made it up as an example! If you've got a stock 2nd gen, you've got far more than 20 more hp left to go.
As far as books, I've been studying these things for about 10 years or so now although probably longer. I think I wrote the first exhaust tech article about 7 years ago or so. Back then I didn't know what I do today since I was concentrating on the math. Understand the concepts first. Worry about math later. It's the concepts that are good for that 90%. The math far less. Even the best race teams in the world use computers and simulation programs to help them now. There's no point trying to figure it all out with a calculator anymore.
An expansion chamber where you have a diverging cone into a larger pipe and then a converging cone back into a smaller pipe also has an effect on power. Typically if designed correctly for your application, it will broaden the powerband a bit at the slight expense of ultimate peak power. This may or may not be desireable.
There are tons of things that play a role in an exhaust and lots of unique things that can be done. You can have dead leg pipes, x-pipes, crossovers, collectors, megaphones, expansion chambers, exhaust boxes, and the list goes on and on. There are lots of ways to do things. In the past I concentrated on trying to learn the math behind it. Now I'm pushing for an understanding of what is actually going on and understanding it. Once you know how certain things play a role, you can start to experiment. If you sit there all day and try to design a system based on math, you are still going to end up with a system that needs to be tweaked and modified to truly do what you want. Here's an example of why.
Let's say we want to calculate a tuned length for a header primary pipe. We go to the trouble to do our math formula and we get a number. Let's say one of our variables, the one for the speed of sound to be exact, was a certain number that basically corresponded to its speed in 1600*F exhaust gas. This formula tells us that we should be tuned to a certain rpm and it's corresponding harmonics. For example in theory we tune for 7000 rpm but the harmonics also tune for 3500 at the 2nd order, 1750 as the 3rd order, etc. You get the idea. However you never see this actually happen because exhaust temps don't remain constant. From the moment that air and fuel get combusted and hit their peak temperature, they immediately start rapidly cooling down. You may have 2000* at the spark plug, 1600* at the exhaust port, and by the time you get out the back of the car through the entire system they may only be 400* or so. You get the idea. When the temperature goes down, the speed of sound changes too and so does tuning.
The speed of sound within the wave length of the first harmonic is going to be faster than the speed of sound through the length of the second harmonic which is more than the 3rd and so forth and so on. What this means is that the return waves do not arrive when we expect them to because all we could do was calculate for fixed variables rather than having a dynamic variable. Suddenly all that math may or may not have been worth it.
The above heat loss issue is compounded by exhaust material. Stainless steel will retain more heat than mild steel will meaning our exhaust gasses will be cooler at the back of the car with the mild steel system than that of the stainless system. This of course applies to other materials too. If we have 2 identical headers but one is stainless and the other is mild steel, they will be tuned completely differently! They may be close but they aren't the same. This makes playing with various designs even more difficult as mild steel is easy to work with an much cheaper. You design a system using mild steel, get it where you want it, and then build it out of stainless only to find it is close but not quite exact in terms of your goals. For street use this really isn't going to be much of an issue but a (good) race team will only prototype with the same material they intend to use for the finished product. A (good) race team will also tune their a/f ratios in the sweet spot of the powerband around egt's. Now you know why. Maintaining a certain egt as long as possible maintains the same tuning for the system as long as possible. If your egt's change too much because you are tuning by a/f ratio only, you may find your powerband falling off a bit in places because of the change in the speed of sound and hence the tuning.
Now don't get all frustrated and scared now that I've said all of this. Many people want all the information they can get on anything that can have any effect at all. Even if it is a small one. It isn't that hard to design a good system for the street. They key is not to get too overwhelmed on the smallest of details that a good race team would focus on. They need that last 1/10th of a horsepower and will go a long way to get it. The first 90% of your power comes with only 10% of the effort. The last 10% of your total power potential takes 90% of your effort. If we only have about 20 more hp to really extract from teh engine, it's not hard to get about 18 of them. Don't ask where I got only 20 more hp from the system though. I made it up as an example! If you've got a stock 2nd gen, you've got far more than 20 more hp left to go.
As far as books, I've been studying these things for about 10 years or so now although probably longer. I think I wrote the first exhaust tech article about 7 years ago or so. Back then I didn't know what I do today since I was concentrating on the math. Understand the concepts first. Worry about math later. It's the concepts that are good for that 90%. The math far less. Even the best race teams in the world use computers and simulation programs to help them now. There's no point trying to figure it all out with a calculator anymore.
01-21-10 | 11:27 AM
#13
Thread Starter
Rotors still spinning
iTrader: (1)
Joined: Jul 2002
Posts: 4,181
Likes: 20
From: Houston
if i understand?
my set-up is 26" - 2" primaries w/ 2 90 bend going to 3" 12" long collector
and sence my muffler(open chamber type straight-thru) is 16" from collector that is the end of the system?
that means my system is only 44"s long! on stock ports? where is this going to limit me?
my set-up is 26" - 2" primaries w/ 2 90 bend going to 3" 12" long collector
and sence my muffler(open chamber type straight-thru) is 16" from collector that is the end of the system?
that means my system is only 44"s long! on stock ports? where is this going to limit me?
Do you know where your power peaks? Judging from your primary header pipe lengths I'd guess you've got some good power in the 6000-6500 rpm range which for stock ports on the street would be fine. The unknown is what effect the 3" collector is having. At a guess I'd say it is hurting your low to midrane power but strengthening your top end over the primary runner tuning. At a guess I'd say for street driving your average powerband is lower than what it could be with the tradeoff that you've probably got some good peak power at redline. I'd personally try to use a 2-1/2" collector instead as I've never has good luck with a pure 3" collector on a stock port engine.
Keep in mind these are guesses on my part. It's your car so only you know what is really going on. I prefer a wider powerband for street use which means I'll sacrifice power above 7000 rpm and shoot for a peak of around 6500-7000 rpm.
01-21-10 | 03:42 PM
#16
Excellent thread rotarygod, I am looking all the info I can get to make a complete custom exhaust system for the 12a installed in my toyota starlet
Thank for your sharing your knowledge
Thank for your sharing your knowledge
01-21-10 | 09:56 PM
#17
Full Member
Joined: Jan 2008
Posts: 122
Likes: 0
From: Huntington Beach, CA
Thank you for writing this! I've always appreciated your devotion to N/A tuning and i've read many of your articles
I would like to ask if you could explain the theory behind expansion chambers in a little more detail and how they work with the entire system that you expalined so well. I'm assuming they don't have the volume to act as an exhaust box so how exactly do they work?
I ask because it seems that the ITS racers love the complete ISC exhaust system which has a 4" expansion chamber after the collector. I'd just like a little more info on how/why that expansion chamber is so affective
Thank you
I would like to ask if you could explain the theory behind expansion chambers in a little more detail and how they work with the entire system that you expalined so well. I'm assuming they don't have the volume to act as an exhaust box so how exactly do they work?
I ask because it seems that the ITS racers love the complete ISC exhaust system which has a 4" expansion chamber after the collector. I'd just like a little more info on how/why that expansion chamber is so affective
Thank you
01-22-10 | 09:08 AM
#18
Thread Starter
Rotors still spinning
iTrader: (1)
Joined: Jul 2002
Posts: 4,181
Likes: 20
From: Houston
I've always loved n/a tuning quite simply because it is harder to make more power. A turbo is very forgiving. You can have an absolutely horrible design and still be relatively quick. A turbo makes it easy for anyone to be fast. I do have my own opinion on how forced induction systems should be designed too though. It doesn't take a lot of talent to go fast with a turbo. It does take talent and knowhow to get really big numbers reliably though.
With n/a tuning, there is far more importance placed on every component. You want more horsepower but at the same time need to balance out drivability, mileage, and noise. You can stick a turbo on a stock engine and hit 300 hp and still retain a good idle, decent mileage, and keep it quiet. It's easy. You let the turbo do all the work. For me, n/a tuning isn't about having more power than the Corvette next door. I don't care what I can do in the quarter mile. I don't care who can beat me. I like n/a tuning because it is a challenge and it forces you to learn. It is definitely not for those who are seeking instant gratification. I like knowing how and why things work like they do. I'm not out to challenge or impress anyone. For me it's all about personal gratification and knowledge.
Having owned a turbo rotary in the past, my current one is a stock '90 GXL. It's still got the paper air filter! Sometimes you get sick of working on them and fixing them and just want to drive. That's why I've left it alone. I've got plans for it though and have the components necessary to do it. I'm just in no hurry. Let's just say it's one of the least popular options on rotaries. That's why I'm going to do it! I never have and want first hand experience.
With n/a tuning, there is far more importance placed on every component. You want more horsepower but at the same time need to balance out drivability, mileage, and noise. You can stick a turbo on a stock engine and hit 300 hp and still retain a good idle, decent mileage, and keep it quiet. It's easy. You let the turbo do all the work. For me, n/a tuning isn't about having more power than the Corvette next door. I don't care what I can do in the quarter mile. I don't care who can beat me. I like n/a tuning because it is a challenge and it forces you to learn. It is definitely not for those who are seeking instant gratification. I like knowing how and why things work like they do. I'm not out to challenge or impress anyone. For me it's all about personal gratification and knowledge.
Having owned a turbo rotary in the past, my current one is a stock '90 GXL. It's still got the paper air filter! Sometimes you get sick of working on them and fixing them and just want to drive. That's why I've left it alone. I've got plans for it though and have the components necessary to do it. I'm just in no hurry. Let's just say it's one of the least popular options on rotaries. That's why I'm going to do it! I never have and want first hand experience.
01-22-10 | 12:19 PM
#20
Old [Sch|F]ool
Joined: May 2001
Posts: 12,635
Likes: 464
From: Cleveland, Ohio, USA
Me, I see unequal runners as broadening the powerband and adding some minor but beneficial unevenness to the engine's power output. Kind of like how V-twins can walk all over even-firing engines under certain conditions. (It has to do with the tires able to regain traction after breaking it momentarily)
FWIW, at least as of several years ago, there was a rule that said Pro Stock engines had to be below a certain displacement, but there was no rule saying all cylinders had to have the same bore or stroke. The engines would end up being two different interlaced V4s.
01-22-10 | 12:26 PM
#21
Not necessarily. If the intake is moved back as you tilt it, the runners can be equalized.
Me, I see unequal runners as broadening the powerband and adding some minor but beneficial unevenness to the engine's power output. Kind of like how V-twins can walk all over even-firing engines under certain conditions. (It has to do with the tires able to regain traction after breaking it momentarily)
Me, I see unequal runners as broadening the powerband and adding some minor but beneficial unevenness to the engine's power output. Kind of like how V-twins can walk all over even-firing engines under certain conditions. (It has to do with the tires able to regain traction after breaking it momentarily)
This thread rocks! I love the raw facts that are jumping out of here.
01-22-10 | 01:15 PM
#22
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From: https://www2.mazda.com/en/100th/
Thank you for writing this! I've always appreciated your devotion to N/A tuning and i've read many of your articles
I would like to ask if you could explain the theory behind expansion chambers in a little more detail and how they work with the entire system that you expalined so well. I'm assuming they don't have the volume to act as an exhaust box so how exactly do they work?
I ask because it seems that the ITS racers love the complete ISC exhaust system which has a 4" expansion chamber after the collector. I'd just like a little more info on how/why that expansion chamber is so affective
Thank you
I would like to ask if you could explain the theory behind expansion chambers in a little more detail and how they work with the entire system that you expalined so well. I'm assuming they don't have the volume to act as an exhaust box so how exactly do they work?
I ask because it seems that the ITS racers love the complete ISC exhaust system which has a 4" expansion chamber after the collector. I'd just like a little more info on how/why that expansion chamber is so affective
Thank you
if you look at the pics they have with that, they have one of how the mufflers LOOK to the ENGINE.
so it looks like the ISC setup ACTS like a megaphone? which then makes sense, we know the megaphone works, its just not done a lot cause its um loud
01-23-10 | 05:29 AM
#25