Proper NA Exhaust Design
09-13-07, 03:34 PM
#1
Proper NA Exhaust Design
I'm looking for information on the optimal design for NA Exhausts. I knew it was posted up somewhere, but I can't find it.
From what I can remember, it was true dual header, to dual presilencer, collecting to a single pipe right where the y-pipe should be into a single outlet muffler.
Now, my questions are, what is the pipe length/width/cross-sectional area that I should use in each area? Is any form of metal better than another, and for what reason is it the best? How wide should the exhaust tip be and should the pipe ever taper up or taper down to a different pipe width?
P.S. If anyone could show me the math, that would be greatly appreciated.
From what I can remember, it was true dual header, to dual presilencer, collecting to a single pipe right where the y-pipe should be into a single outlet muffler.
Now, my questions are, what is the pipe length/width/cross-sectional area that I should use in each area? Is any form of metal better than another, and for what reason is it the best? How wide should the exhaust tip be and should the pipe ever taper up or taper down to a different pipe width?
P.S. If anyone could show me the math, that would be greatly appreciated.
09-13-07, 04:17 PM
#2
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RB got it right with their collected header & pre-silencer.
If you go dual, go all the way to through dual pre-silencers to dual mufflers.
Link to full dual stereo sound bite
Link to short video from inside
If you go dual, go all the way to through dual pre-silencers to dual mufflers.
Link to full dual stereo sound bite
Link to short video from inside
Last edited by SureShot; 09-13-07 at 04:23 PM.
09-13-07, 05:00 PM
#5
I was planning on doing the dual header and presilencer into the single Y and mufflers because I assumed it would not decrease performance from a single header presilencer and not be as loud as true dual.
I would also have the ability to switch to true dual if I was racing.
09-13-07, 05:33 PM
#7
True duals with the Side exits like the FC race car? I'd keep it a tad farther than right in front of the REAR tires but then again i'm no mazda race car tech.
Last edited by phoenix7; 12-23-07 at 08:52 PM.
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09-13-07, 05:52 PM
#8
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The only answer is it depends. It depends on the porting, both intake and exhaust, the header ID, the collector shape, the downstream components and stuff like that. There's no one answer, many systems have been tried with varying success with different cars, everything from true duals, to merging at the axle, to merging about a foot after the engine. All work in different situations.
09-13-07, 07:34 PM
#11
The thing about exhausts is that you only have X amount of restriction in the stock exhaust. No matter how much you try, you can't remove more than 100% of this restriction. And removing 95% of it will be 10 times harder than removing 90% of it.
I'd say the ideal exhaust would replace the catalytic converter and mufflers only, while leaving the rest stock. This will remove almost all of the restriction at a far lower cost than true duals (which is only a little better). Oh, and mind your 5th and 6th ports of course.
New cars come with fairly unrestrictive exhausts from the factory. So I imagine a leading Mazdaspeed engineer would use stock or whatever mufflers have the sound he likes. Though you can upgrade a new car to a huge expensive exhaust for tiny HP gains.
I'd say the ideal exhaust would replace the catalytic converter and mufflers only, while leaving the rest stock. This will remove almost all of the restriction at a far lower cost than true duals (which is only a little better). Oh, and mind your 5th and 6th ports of course.
New cars come with fairly unrestrictive exhausts from the factory. So I imagine a leading Mazdaspeed engineer would use stock or whatever mufflers have the sound he likes. Though you can upgrade a new car to a huge expensive exhaust for tiny HP gains.
09-13-07, 07:39 PM
#12
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There's more to it than just restriction, it's a series of pulses and a properly designed header can help with extracting the exhaust out of each rotor housing to give more power.
09-13-07, 07:51 PM
#13
No, no there isn't. Exhausts are passive devices. They don't pull.
Maybe they just didn't cover harmonics in my fluid dynamics classes, but the claims I've seen on headers seem hokey at best. And the best evidence I've seen are some poorly photoshopped dyno sheets (hey look, the static on the new line matches the static on the old line!, etc.). When people post their dynos on these forums their entire exhausts (headers included) are equal or less what is claimed only for the header. But I can see how headers would help a little by smoothing bends. It's just that smoothing out that little bend does a lot less than, for example, dealing with the two abrupt 180 degree turns in the mufflers.
Maybe they just didn't cover harmonics in my fluid dynamics classes, but the claims I've seen on headers seem hokey at best. And the best evidence I've seen are some poorly photoshopped dyno sheets (hey look, the static on the new line matches the static on the old line!, etc.). When people post their dynos on these forums their entire exhausts (headers included) are equal or less what is claimed only for the header. But I can see how headers would help a little by smoothing bends. It's just that smoothing out that little bend does a lot less than, for example, dealing with the two abrupt 180 degree turns in the mufflers.
09-13-07, 10:14 PM
#15
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Yea, they don't really cover that, but then why would Mazda do the whole VDI thing if the intake and exhaust were static devices. The fact is there's pressure waves and they affect things. That's why different length headers perform differently, and why equal length is desirable. I don't know much about header theory, but it's more than just a minimum backpressure persuit. With a 2 stroke I've heard of dirt bikes loosing significant power if the expansion chamber is dented, proof that harmonics and the pulses really do matter.
09-13-07, 11:34 PM
#17
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The road race headers from racing beat are seperate.. My 87' was fitted that and I Had both of the 2" pipes runing side by side till the y-pipe then they just seperated to the magnaflow exhaust's. It sounded different though... It pulsated too much. If I parked it with the tail pipes towards the house I could vibrated everything in the house... Things fell off the table and everything... the weird part was that it was not that loud... I asked a friend of mine that was more informed on the subject to fill me in and he said that a mazda stock manifold was designed to have the peaks of one rotor's pulse pass by on a deppression of the other rotor's pulses... thus deadning the pulses... but since they were seperate the "true" pulses were presnent and the car vibrated everything.
09-14-07, 07:22 AM
#18
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OK – some basic points:
Auto engines don’t breathe in a continuous flow, they breathe in short pulses, especially the rotary.
When the intake & exhaust tubes length matches an even multiple of the speed of sound divided by the pulse frequency, you get a standing wave (or tune).
Longer tubes tune at lower frequencies, shorter tubes at higher frequencies. (Think tubas & trumpets)
When these pressure waves arrive at the end of the tube in tune with the port opening frequency, you get a nice boost in flow at the port. (On the exhaust side it’s often called scavenging, on the intake side, dynamic tune)
If you ever get a chance to drive with the header off, you will be amazed at the power loss compared to even an untuned exhaust.
Besides the tube length, other tuning variables are the collection point for multiple ports, and the crossover point for multiple tubes.
-Bill
(edit)
My 91NA had full duals.
I liked that setup for daily driving because the sweet spot was low (around 3500).
That low end grunt was fun when zipping around town.
You might notice it in the video.
Auto engines don’t breathe in a continuous flow, they breathe in short pulses, especially the rotary.
When the intake & exhaust tubes length matches an even multiple of the speed of sound divided by the pulse frequency, you get a standing wave (or tune).
Longer tubes tune at lower frequencies, shorter tubes at higher frequencies. (Think tubas & trumpets)
When these pressure waves arrive at the end of the tube in tune with the port opening frequency, you get a nice boost in flow at the port. (On the exhaust side it’s often called scavenging, on the intake side, dynamic tune)
If you ever get a chance to drive with the header off, you will be amazed at the power loss compared to even an untuned exhaust.
Besides the tube length, other tuning variables are the collection point for multiple ports, and the crossover point for multiple tubes.
-Bill
(edit)
My 91NA had full duals.
I liked that setup for daily driving because the sweet spot was low (around 3500).
That low end grunt was fun when zipping around town.
You might notice it in the video.
Last edited by SureShot; 09-14-07 at 07:32 AM.
09-14-07, 10:54 AM
#19
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The only answer is it depends. It depends on the porting, both intake and exhaust, the header ID, the collector shape, the downstream components and stuff like that. There's no one answer, many systems have been tried with varying success with different cars, everything from true duals, to merging at the axle, to merging about a foot after the engine. All work in different situations.
for a stock intake fc, street car, the header seems to work just as well as removing the cats, i think the vdi works best with some backpressure.
09-14-07, 11:54 AM
#20
You're thinking way too far into it.
The SDJ headers are the best ones out there but are more expensive than RB by a margin.
If you arent that serious i'd say just get an RB header a high flow 2.5" cat, and then have the exhaust shop down the road make you a cat back system with whatever muffler(s) you want.
The SDJ headers are the best ones out there but are more expensive than RB by a margin.
If you arent that serious i'd say just get an RB header a high flow 2.5" cat, and then have the exhaust shop down the road make you a cat back system with whatever muffler(s) you want.
09-14-07, 11:55 AM
#21
This is for my ITS car.......yeah, it's serious.
SDJ has a track header, but I refuse to believe race headers are a one-size fit all approach. If anyone can show me the math on how they determined what their optimal exhaust components should be, that would be very much appreciated.
SDJ has a track header, but I refuse to believe race headers are a one-size fit all approach. If anyone can show me the math on how they determined what their optimal exhaust components should be, that would be very much appreciated.
09-14-07, 12:07 PM
#22
From what i've heard that there have been people who dynoed it and it made more power than RB.
I would ask chris ludwig, he lives near me, he has an its car and he's pretty damn experienced a local engine builder. He made 172 HP out of a stock ECU stock port car.
Should've said it was for an ITS car in the first place.
Personally, if it were me, i'd just run the header to a 2.5" XR-1 and then a straight pipe out the back, but what do i know.
I would ask chris ludwig, he lives near me, he has an its car and he's pretty damn experienced a local engine builder. He made 172 HP out of a stock ECU stock port car.
Should've said it was for an ITS car in the first place.
Personally, if it were me, i'd just run the header to a 2.5" XR-1 and then a straight pipe out the back, but what do i know.
09-14-07, 12:12 PM
#23
I've spoken to him, and used his ECU. Granted his run was on an Rtek crammed into the Stock ECU box, the same that I'm using now.
Baseline two nights before the dyno tuning sessions at KDR: 155 whp
Baseline day of: 140-143 whp I forget exactly
After tune: 153 whp
It was really hot that day, and I wasn't really making any power, but the car, when the ambient temps cool down, definitely feels like a 170 whp car.
We went conservative and aimed for 13.5-13.6 on the AFR scales.
The reason why I posted this thread was that awhile ago, there was a debate betweem Nihilantic and Icemark on what the best exhaust for an N/A second gen was. I also remember seeing a thread with Aaron Cake stating that the RB Road Race was the best mass-porduced approximation of what an optimal exhaust should be.
I can't find any of those threads anymore, which is why I posted up this one.
Baseline two nights before the dyno tuning sessions at KDR: 155 whp
Baseline day of: 140-143 whp I forget exactly
After tune: 153 whp
It was really hot that day, and I wasn't really making any power, but the car, when the ambient temps cool down, definitely feels like a 170 whp car.
We went conservative and aimed for 13.5-13.6 on the AFR scales.
The reason why I posted this thread was that awhile ago, there was a debate betweem Nihilantic and Icemark on what the best exhaust for an N/A second gen was. I also remember seeing a thread with Aaron Cake stating that the RB Road Race was the best mass-porduced approximation of what an optimal exhaust should be.
I can't find any of those threads anymore, which is why I posted up this one.
09-14-07, 01:05 PM
#24
Wanna bet?
There is more to it than just flow. If this wasn't true then the best exhaust would be no exhaust. Take the exhaust completely off of the car and drive it open port. While you are trying to cover your bleeding ears, you'll notice that the car doesn't make crap for power. Why? The exhaust isn't helping the air flow away from the port.
Fluid mechanics is a very interesting topic and definitely good to know. Realize though that we don't have constant flow in the intake or exhaust system. This isn't a river. We have pulses. Each pulse is a high pressure zone moving through the pipe. However it is followed by a low pressure zone behind it. We want the low behind it to help "pull" the next pulse through the pipe. Proper exhaust scavenging does this and we pick up power. We optimally want these pulses equally spaced which is why even length headers are best.
We also have another tuning benefit and that is acoustics. Your intake runners are acoustically tuned. Even VDI is an acoustic tuning method as the return pulses return at the speed of sound to the other side. Scavenging is dependent on rpm as faster gasses are at lower pressure. We don't want these waves to be at the speed of sound. Typically .6 mach is about the max we want. 2 totally different tuning phenomenon in the same place.
There is no one proper exhaust. Again as with everything, it depends. There are 3 basic systems out there. The first is the short primary system. This utilizes a header that collects conventionally near the engine. Typically at lengths of around 24" or so. Some are more, some are less. Varying the length changes the tuning. Technically the stock exhaust box is a short primary as the effective runner length is about 2" (which tunes it to about 7000 rpm or so) and then collects in a large open exhaust manifold.
Next we have a long primary. This is seem more often on 1st gens and some race cars. This is also a header system but it collects near the rear of the car before the muffler. Lengths over 100" are common. The powerband is different with these as opposed to a short primary. Some people say they make more power than a short primary and others say the opposite. If done properly they make more average power but again, it depends.
Tuning length is more involved than just making a pipe longer to tune lower. If we tune at one rpm, we also tune at it's harmonics. Let's say we tune a pipe for peak power at 8000 rpm. It is also going to benefit at 4000, 2000, and 1000 rpm's with lowering degrees of benefit for each harmonic lower. Between these rpms however benefit falls off and power can actually suffer. You can't have it all! If we tuned a long primary for a benefit at X rpm and then had a short primary tuned for max benefit at Y rpm, the fact that they are tuned at different rpms will allow one to outperform the other. What if the long primary were tuned such that it had a valley at 7000 rpm but the short primary was tuned for 7000? The short would make more power there. You get the idea.
The reason a long primary works so well is due to the number of pulses in the pipe at any one time. If we have a longer pipe, we have more pulses that can pull on each other. There is of course always a law of diminishing returns though so don't think going longer indefinitely is a good thing.
The last system is a true dual. This system does not scavenge. Why? You have to have a collected system to scavenge. I know I said that pulses pull on each other and they do. However it's the pulses from the other rotor that do so. Remember each rotor has some overlap to the other. As the pulse from one rotor is slowing down, the other rotor has opened up and occupies the same space as a part of the previous pulse. It helps pull it down the pipe. Think of this as drafting a semi on the freeway. If the spaces are too far out and don't overlap much, such as getting farther and farther away from the semi, the benefit is diminished.
If a true dual doesn't scavenge, why do they make decent power? Acoustic tuning! Yes acoustics can play that large of a role in tuning. Keep in mind the more overlap your porting has such as bridge or peripheral porting, the more critical it is that you have a scavenging collected exhaust system. Basically a true dual is nice on a stock or streetport, but anything more aggressive than this and you really need to pick one of the other 2 for max benefit.
BTW: My personal favorite system, and I've had all 3, is the long primary.
I could write all day on this topic.
There is more to it than just flow. If this wasn't true then the best exhaust would be no exhaust. Take the exhaust completely off of the car and drive it open port. While you are trying to cover your bleeding ears, you'll notice that the car doesn't make crap for power. Why? The exhaust isn't helping the air flow away from the port.
Fluid mechanics is a very interesting topic and definitely good to know. Realize though that we don't have constant flow in the intake or exhaust system. This isn't a river. We have pulses. Each pulse is a high pressure zone moving through the pipe. However it is followed by a low pressure zone behind it. We want the low behind it to help "pull" the next pulse through the pipe. Proper exhaust scavenging does this and we pick up power. We optimally want these pulses equally spaced which is why even length headers are best.
We also have another tuning benefit and that is acoustics. Your intake runners are acoustically tuned. Even VDI is an acoustic tuning method as the return pulses return at the speed of sound to the other side. Scavenging is dependent on rpm as faster gasses are at lower pressure. We don't want these waves to be at the speed of sound. Typically .6 mach is about the max we want. 2 totally different tuning phenomenon in the same place.
There is no one proper exhaust. Again as with everything, it depends. There are 3 basic systems out there. The first is the short primary system. This utilizes a header that collects conventionally near the engine. Typically at lengths of around 24" or so. Some are more, some are less. Varying the length changes the tuning. Technically the stock exhaust box is a short primary as the effective runner length is about 2" (which tunes it to about 7000 rpm or so) and then collects in a large open exhaust manifold.
Next we have a long primary. This is seem more often on 1st gens and some race cars. This is also a header system but it collects near the rear of the car before the muffler. Lengths over 100" are common. The powerband is different with these as opposed to a short primary. Some people say they make more power than a short primary and others say the opposite. If done properly they make more average power but again, it depends.
Tuning length is more involved than just making a pipe longer to tune lower. If we tune at one rpm, we also tune at it's harmonics. Let's say we tune a pipe for peak power at 8000 rpm. It is also going to benefit at 4000, 2000, and 1000 rpm's with lowering degrees of benefit for each harmonic lower. Between these rpms however benefit falls off and power can actually suffer. You can't have it all! If we tuned a long primary for a benefit at X rpm and then had a short primary tuned for max benefit at Y rpm, the fact that they are tuned at different rpms will allow one to outperform the other. What if the long primary were tuned such that it had a valley at 7000 rpm but the short primary was tuned for 7000? The short would make more power there. You get the idea.
The reason a long primary works so well is due to the number of pulses in the pipe at any one time. If we have a longer pipe, we have more pulses that can pull on each other. There is of course always a law of diminishing returns though so don't think going longer indefinitely is a good thing.
The last system is a true dual. This system does not scavenge. Why? You have to have a collected system to scavenge. I know I said that pulses pull on each other and they do. However it's the pulses from the other rotor that do so. Remember each rotor has some overlap to the other. As the pulse from one rotor is slowing down, the other rotor has opened up and occupies the same space as a part of the previous pulse. It helps pull it down the pipe. Think of this as drafting a semi on the freeway. If the spaces are too far out and don't overlap much, such as getting farther and farther away from the semi, the benefit is diminished.
If a true dual doesn't scavenge, why do they make decent power? Acoustic tuning! Yes acoustics can play that large of a role in tuning. Keep in mind the more overlap your porting has such as bridge or peripheral porting, the more critical it is that you have a scavenging collected exhaust system. Basically a true dual is nice on a stock or streetport, but anything more aggressive than this and you really need to pick one of the other 2 for max benefit.
BTW: My personal favorite system, and I've had all 3, is the long primary.
I could write all day on this topic.
09-14-07, 01:38 PM
#25
So, on stock ports, you'd want to stay true dual? (Say......for an ITS-race car)
And for a ported 4-port NA engine with an aggressive street port (Think 13BT, RE, REW or 20B-REW with S5 NA or RX-8 rotors), you'd want to go with a long primary?
How does exhaust piping width/cross-sectional area and muffler tip size play into this?
Also, how does the Y-pipe play a role into this? Say you have a short primary, does the Y-pipe solely lower noise while maintaing flow? Is it that much of a restriction? Or for instance, you have a long primary system, but want to keep two mufflers. How far apart would you have to place the y-pipe? Would it make any sense to place the Y directly at the collection site? I would think there would be too much turbulence there.
And for a ported 4-port NA engine with an aggressive street port (Think 13BT, RE, REW or 20B-REW with S5 NA or RX-8 rotors), you'd want to go with a long primary?
How does exhaust piping width/cross-sectional area and muffler tip size play into this?
Also, how does the Y-pipe play a role into this? Say you have a short primary, does the Y-pipe solely lower noise while maintaing flow? Is it that much of a restriction? Or for instance, you have a long primary system, but want to keep two mufflers. How far apart would you have to place the y-pipe? Would it make any sense to place the Y directly at the collection site? I would think there would be too much turbulence there.