Dual Primary
02-28-03, 05:14 AM
#1
ROTARY POWER
Thread Starter
Dual Primary
simple question............please give me your opinion and what you are using
what type of exhaust are you running?
Is it: short primary, long primary, does it collect before or after the axle, does it ever collect or are you running two straight pipes to two seperate mufflers with no connections and mounted side by side?
I am trying to understand which is better regardless of the porting on a 6 port se motor looking for high end power and no real need for low end.
Thanks for your help if you can shed some light on this for me!
(i am considering the dual side/side muffers)
what type of exhaust are you running?
Is it: short primary, long primary, does it collect before or after the axle, does it ever collect or are you running two straight pipes to two seperate mufflers with no connections and mounted side by side?
I am trying to understand which is better regardless of the porting on a 6 port se motor looking for high end power and no real need for low end.
Thanks for your help if you can shed some light on this for me!
(i am considering the dual side/side muffers)
02-28-03, 06:06 AM
#2
Keep Right Except to Pass
02-28-03, 09:24 AM
#3
Check out my thread on the Warlock muffler in the rotary performance section. I've been playing with different setups lately. My engine is streetported though but I have quite a bit of experience with stock port exhaust systems as well. Heres my thoughts on each system.
This applies to a streetported GSL-SE engine with a good amount of port overlap. Others may be different:
Short primary: Better than the stock exhaust system anyday. A nice power increase with more noticable torque. Starts pulling really good above about 5000 rpm or so but getting stronger all the way to redline. Wish I could shift gears higher up.
Long primary: A noticable amount of power more than a short primary with more usable torque throughout the entire rpm range. Great lowend power but starts running lean after about 6000 rpm or so. No point to shifting higher than 7000 rpm. I suspect this is due to superior exhaust scavenging which helps pull a greater amount of air into the engine during the next cycle.
True dual: Good lowend but decreasing rapidly in usable power the higher in the rpm range. Lack of inertial scavenging from the other port results in no additional air being sucked into the engine from the velocity of escaping exhaust gasses other than what the engine can do on its own. You may have to think about that one for a while. A simpler way to explain that escapes me right now.
Here are my findings on STOCK ported engines. This is based on a 2nd gen engine. Again yours may respond different:
Short primary: Get that header on there and wow way more power! Gotta love that header! Car gets louder though. Very drivable with a nice exhaust tone. Car makes more power everywhere.
Long primary: Didn't try it on the 2nd gen.
True Duals: Fantastic power! Short primary has nothing on it in terms of power but I hate the sound of it. Definitely gets louder. Cars gas mileage went up considerably. Much more drivable around town. Best all around system for stock ports in terms of performance. I just wish that sound was different.
Obviously different port styles have different exhaust systems they favor. Bridgeport and peripheral port n/a's get even more finicky as to what does and doesn't work. If its just stock damn near anything is an improvement. My vote goes to the true dual on stock ports if you can tolerate the sound. If it is ported I say go for the long primary.
This applies to a streetported GSL-SE engine with a good amount of port overlap. Others may be different:
Short primary: Better than the stock exhaust system anyday. A nice power increase with more noticable torque. Starts pulling really good above about 5000 rpm or so but getting stronger all the way to redline. Wish I could shift gears higher up.
Long primary: A noticable amount of power more than a short primary with more usable torque throughout the entire rpm range. Great lowend power but starts running lean after about 6000 rpm or so. No point to shifting higher than 7000 rpm. I suspect this is due to superior exhaust scavenging which helps pull a greater amount of air into the engine during the next cycle.
True dual: Good lowend but decreasing rapidly in usable power the higher in the rpm range. Lack of inertial scavenging from the other port results in no additional air being sucked into the engine from the velocity of escaping exhaust gasses other than what the engine can do on its own. You may have to think about that one for a while. A simpler way to explain that escapes me right now.
Here are my findings on STOCK ported engines. This is based on a 2nd gen engine. Again yours may respond different:
Short primary: Get that header on there and wow way more power! Gotta love that header! Car gets louder though. Very drivable with a nice exhaust tone. Car makes more power everywhere.
Long primary: Didn't try it on the 2nd gen.
True Duals: Fantastic power! Short primary has nothing on it in terms of power but I hate the sound of it. Definitely gets louder. Cars gas mileage went up considerably. Much more drivable around town. Best all around system for stock ports in terms of performance. I just wish that sound was different.
Obviously different port styles have different exhaust systems they favor. Bridgeport and peripheral port n/a's get even more finicky as to what does and doesn't work. If its just stock damn near anything is an improvement. My vote goes to the true dual on stock ports if you can tolerate the sound. If it is ported I say go for the long primary.
02-28-03, 11:42 AM
#5
I personally think the tone is atrocious. There are a few people that like it though. It sounds too much like a Harley-Davidson/lawnmower cross which I'm not fond of. Being unmixed with the other rotors exhaust also keeps it louder than a collected system all things being equal. this is easily remedied though. My setup currently sounds like you are playing a chainsaw through a Marshall amp!!! A little too loud. The true duals isn't that bad as far as loudness is concerned if you do it right. You never know you might like the sound. Then again...
02-28-03, 11:48 AM
#6
true dual sounds like a v8 at idle and really low engine speed.
I ran just a racingbeat roadrace header and a streetport section, no rear muffler for a few days before I finished my exhaust.
it sounded ******* awsome but it was to loud for the street.
I ran just a racingbeat roadrace header and a streetport section, no rear muffler for a few days before I finished my exhaust.
it sounded ******* awsome but it was to loud for the street.
02-28-03, 02:27 PM
#7
ROTARY POWER
Thread Starter
So I guess the true dual to two seperate mufflers is for me. I dont really care about the volume as this is a track car. but should I have mentioned that the 5/6th ports are wired open and is this the system that is going to let me make the most power over 5000rpms with the stock ports and wired 5/6ths?
this is a lot of help and i appreciate all the responses.
this is a lot of help and i appreciate all the responses.
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02-28-03, 03:01 PM
#8
Wiring open the auxilary ports gives you ZERO gain over not wiring them and letting them function properly. Why would it? The only thing that has changed is that you LOSE power below about 3800 rpm or so. If you have no emissions and hence no air pump, or back pressure sensing tube from the exhaust then it is logical to do this. If you want to actually get a gain, remove the actuators and actuator rods entirely. This will get everything out of the air stream. The rods take up alot of runner area and when you remove them you get this much more runner volume for air to flow down! More air will be flowing through the aux. ports. It is less turbulent and of higher velocity too. Radius the factory sleeve, or buy Pineapple sleeves and glue them in the open position (minus actuator rods). This will give the air a nice gentle turn instead of a brick wall to hit. You'll notice a top end difference by doing all of this. Getting back to your last question though, the true duals is going to give you the greatest usable average power across the entire powerband. Peak power may or may not be slightly lower than say a long primary system but you are going to be faster. Its not peak power that wins races, its average power. Peak power numbers are only good for bragging and selling product. They tell us nothing terribly useful.
02-28-03, 03:30 PM
#9
Absolute Power is Awesome
Originally posted by rotarygod
Wiring open the auxilary ports gives you ZERO gain over not wiring them and letting them function properly. Why would it? The only thing that has changed is that you LOSE power below about 3800 rpm or so. If you have no emissions and hence no air pump, or back pressure sensing tube from the exhaust then it is logical to do this. If you want to actually get a gain, remove the actuators and actuator rods entirely. This will get everything out of the air stream. The rods take up alot of runner area and when you remove them you get this much more runner volume for air to flow down! More air will be flowing through the aux. ports. It is less turbulent and of higher velocity too. Radius the factory sleeve, or buy Pineapple sleeves and glue them in the open position (minus actuator rods). This will give the air a nice gentle turn instead of a brick wall to hit. You'll notice a top end difference by doing all of this. Getting back to your last question though, the true duals is going to give you the greatest usable average power across the entire powerband. Peak power may or may not be slightly lower than say a long primary system but you are going to be faster. Its not peak power that wins races, its average power. Peak power numbers are only good for bragging and selling product. They tell us nothing terribly useful.
Wiring open the auxilary ports gives you ZERO gain over not wiring them and letting them function properly. Why would it? The only thing that has changed is that you LOSE power below about 3800 rpm or so. If you have no emissions and hence no air pump, or back pressure sensing tube from the exhaust then it is logical to do this. If you want to actually get a gain, remove the actuators and actuator rods entirely. This will get everything out of the air stream. The rods take up alot of runner area and when you remove them you get this much more runner volume for air to flow down! More air will be flowing through the aux. ports. It is less turbulent and of higher velocity too. Radius the factory sleeve, or buy Pineapple sleeves and glue them in the open position (minus actuator rods). This will give the air a nice gentle turn instead of a brick wall to hit. You'll notice a top end difference by doing all of this. Getting back to your last question though, the true duals is going to give you the greatest usable average power across the entire powerband. Peak power may or may not be slightly lower than say a long primary system but you are going to be faster. Its not peak power that wins races, its average power. Peak power numbers are only good for bragging and selling product. They tell us nothing terribly useful.
02-28-03, 04:38 PM
#10
I think you misunderstand what I'm saying. Without the sleeve installed there is a horrible turn at the back of the auxillary port that is hurting airflow. It is even still there on the sleeves. The air has to turn a 90 degree bend. By installing radiused sleeves glued in the open position you no longer have this 90 degree turn but rather a gentle radius for air to enter the engine. Since either way the port is always open there is no more or less timing. Only with a closed sleeve would there be less timing.
02-28-03, 05:27 PM
#11
Absolute Power is Awesome
Originally posted by rotarygod
I think you misunderstand what I'm saying. Without the sleeve installed there is a horrible turn at the back of the auxillary port that is hurting airflow. It is even still there on the sleeves. The air has to turn a 90 degree bend. By installing radiused sleeves glued in the open position you no longer have this 90 degree turn but rather a gentle radius for air to enter the engine. Since either way the port is always open there is no more or less timing. Only with a closed sleeve would there be less timing.
I think you misunderstand what I'm saying. Without the sleeve installed there is a horrible turn at the back of the auxillary port that is hurting airflow. It is even still there on the sleeves. The air has to turn a 90 degree bend. By installing radiused sleeves glued in the open position you no longer have this 90 degree turn but rather a gentle radius for air to enter the engine. Since either way the port is always open there is no more or less timing. Only with a closed sleeve would there be less timing.
Removing the sleeve completely increases the cross sectional area of the port, increasing the mass flow of air though the port, provided the hole in the side housing is larger than the hole in the sleeve (I'm not sure about that)
02-28-03, 05:57 PM
#13
The outside of a turn makes a huge difference in the flow characteristics. Air has mass. When fuel is added to it then it obviously has more mass. This mass is getting forced towards the outside of the bend. When you turn really fast to the right in your car you get thrown to the outside (left) of the car not towards the inside (right). Air does the same thing. Yes radiusing the inner edge does help. I do this on all of my engines but it is really just removing turbulence from that sharp edge. It doesn't mean that all of the flow is on the inner edge. Airflow through an engine is unaffected as to whether it is being sucked in or pushed in. It still flows the same way. A sharper turn radius has a negative effect because the air can't turn fast enough and more of it gets pushed to the outside by inertia. This is the busy area of the port. Some air is traveling down the inner surface but not as much. Lets use a very recognizable fluid as an example. A river. Look at the bends of a river. Where does the water move the fastest? The outside of the turn. This is also where the greatest amount of erosion takes place since this is the busiest area. The relatively stagnant inner bend of the river runs much slower. Any change here will have less of an impact on total flow than the outside. Also remember that we have other forces at work in our engines, namely acoustic ramcharging. A soundwave traveling back to the port is going to have a harder time entering through a smaller opening such as a door in a room than if it were a constant size opening such as a pipe. Muffler? Acoustic pressure waves also gives the engine a boost in power. Yes, we have plenum chambers with stagnant areas in them but they function very differently. First off, they are much larger and air has a much easier time turning inside this area. The plenum chamber is there because we are tuning the intake runners to a certain length. This length is determined by where the runners terminate into a larger area regardless of whether its a plenum or the open atmosphere. Air has no trouble turning outside in an area as large as the Earth's atmosphere. Got some neat weather patterns to prove it. In an area as small as a port runner air molecules are proportionately larger in relation to the area of the port. What I mean by this is that it takes fewer molecules of air to span the open area of a smaller area. This makes good flow all the more important. Ever tried to drive 150 mph and stay in only one lane on the road through a turn? Pretty tough to do at high speed. It would be even harder if we were between two concrete barriers and the turn was just an opening before the end of the walls. Try going this fast on a 6 lane freeway. Easy. The difference being that the air doesn't have the common sense that we do to take the inner apex of a turn and hence the shortest distance. If we didn't then we'd be riding the concrete barrier around the outside of the turn like the air does. I could write all day about this so I'll stop here. You get the idea.
Last edited by rotarygod; 02-28-03 at 06:05 PM.
02-28-03, 06:41 PM
#14
ROTARY POWER
Thread Starter
I dont have any emissions contol or airpump, but i never considered removing the actuators.......until now.
I'm going to look into that now, so thanks. But when you guys say true dual, do you mean never collecting at any point, not even with a 'x' or 'H' pipe? It seems from othe comments some people consider these slight mix points as still being a true dual primary.
Does the "average overall power gain" out way the weight gain of a second muffler and more piping?
Any pictures out there of these true dual primary setups?
I'm going to look into that now, so thanks. But when you guys say true dual, do you mean never collecting at any point, not even with a 'x' or 'H' pipe? It seems from othe comments some people consider these slight mix points as still being a true dual primary.
Does the "average overall power gain" out way the weight gain of a second muffler and more piping?
Any pictures out there of these true dual primary setups?
02-28-03, 08:02 PM
#15
Absolute Power is Awesome
Originally posted by rotarygod
The outside of a turn makes a huge difference in the flow characteristics. Air has mass. When fuel is added to it then it obviously has more mass. This mass is getting forced towards the outside of the bend. When you turn really fast to the right in your car you get thrown to the outside (left) of the car not towards the inside (right). Air does the same thing. Yes radiusing the inner edge does help. I do this on all of my engines but it is really just removing turbulence from that sharp edge. It doesn't mean that all of the flow is on the inner edge. Airflow through an engine is unaffected as to whether it is being sucked in or pushed in. It still flows the same way. A sharper turn radius has a negative effect because the air can't turn fast enough and more of it gets pushed to the outside by inertia. This is the busy area of the port. Some air is traveling down the inner surface but not as much. Lets use a very recognizable fluid as an example. A river. Look at the bends of a river. Where does the water move the fastest? The outside of the turn. This is also where the greatest amount of erosion takes place since this is the busiest area. The relatively stagnant inner bend of the river runs much slower. Any change here will have less of an impact on total flow than the outside. Also remember that we have other forces at work in our engines, namely acoustic ramcharging. A soundwave traveling back to the port is going to have a harder time entering through a smaller opening such as a door in a room than if it were a constant size opening such as a pipe. Muffler? Acoustic pressure waves also gives the engine a boost in power. Yes, we have plenum chambers with stagnant areas in them but they function very differently. First off, they are much larger and air has a much easier time turning inside this area. The plenum chamber is there because we are tuning the intake runners to a certain length. This length is determined by where the runners terminate into a larger area regardless of whether its a plenum or the open atmosphere. Air has no trouble turning outside in an area as large as the Earth's atmosphere. Got some neat weather patterns to prove it. In an area as small as a port runner air molecules are proportionately larger in relation to the area of the port. What I mean by this is that it takes fewer molecules of air to span the open area of a smaller area. This makes good flow all the more important. Ever tried to drive 150 mph and stay in only one lane on the road through a turn? Pretty tough to do at high speed. It would be even harder if we were between two concrete barriers and the turn was just an opening before the end of the walls. Try going this fast on a 6 lane freeway. Easy. The difference being that the air doesn't have the common sense that we do to take the inner apex of a turn and hence the shortest distance. If we didn't then we'd be riding the concrete barrier around the outside of the turn like the air does. I could write all day about this so I'll stop here. You get the idea.
The outside of a turn makes a huge difference in the flow characteristics. Air has mass. When fuel is added to it then it obviously has more mass. This mass is getting forced towards the outside of the bend. When you turn really fast to the right in your car you get thrown to the outside (left) of the car not towards the inside (right). Air does the same thing. Yes radiusing the inner edge does help. I do this on all of my engines but it is really just removing turbulence from that sharp edge. It doesn't mean that all of the flow is on the inner edge. Airflow through an engine is unaffected as to whether it is being sucked in or pushed in. It still flows the same way. A sharper turn radius has a negative effect because the air can't turn fast enough and more of it gets pushed to the outside by inertia. This is the busy area of the port. Some air is traveling down the inner surface but not as much. Lets use a very recognizable fluid as an example. A river. Look at the bends of a river. Where does the water move the fastest? The outside of the turn. This is also where the greatest amount of erosion takes place since this is the busiest area. The relatively stagnant inner bend of the river runs much slower. Any change here will have less of an impact on total flow than the outside. Also remember that we have other forces at work in our engines, namely acoustic ramcharging. A soundwave traveling back to the port is going to have a harder time entering through a smaller opening such as a door in a room than if it were a constant size opening such as a pipe. Muffler? Acoustic pressure waves also gives the engine a boost in power. Yes, we have plenum chambers with stagnant areas in them but they function very differently. First off, they are much larger and air has a much easier time turning inside this area. The plenum chamber is there because we are tuning the intake runners to a certain length. This length is determined by where the runners terminate into a larger area regardless of whether its a plenum or the open atmosphere. Air has no trouble turning outside in an area as large as the Earth's atmosphere. Got some neat weather patterns to prove it. In an area as small as a port runner air molecules are proportionately larger in relation to the area of the port. What I mean by this is that it takes fewer molecules of air to span the open area of a smaller area. This makes good flow all the more important. Ever tried to drive 150 mph and stay in only one lane on the road through a turn? Pretty tough to do at high speed. It would be even harder if we were between two concrete barriers and the turn was just an opening before the end of the walls. Try going this fast on a 6 lane freeway. Easy. The difference being that the air doesn't have the common sense that we do to take the inner apex of a turn and hence the shortest distance. If we didn't then we'd be riding the concrete barrier around the outside of the turn like the air does. I could write all day about this so I'll stop here. You get the idea.
Your analogy about a river assumes errosion is due to a solid body type momentum somehow. In actuality, the sand, dirt, ect on the outside bend of a river is deposited to the inside the of bend due to secondary flow effects. The water at the outside of the bend is moving slowly, the inside is moving quickly, the pressure at the outside of the bend is higher than the inside causing a secondary flow of fluid from the outside of the bend to the inside, this secondary flow carries the material from the outside of the bend to the inside. THIS is why the bend in a river grows. It's also why loose tea leaves collect in the center of a cup if you stir the water.
If you want to REALLY understand fluid flows, I can refer you to some very informative texts.
03-01-03, 02:38 AM
#16
OMG that doesn't even deserve a response as any form of intelligence is wasted at this point but I'll still deal with the river analogy since any geology professor would laugh at that response and I don't want any other RX-7 people to believe something that isn't even close to true. You are correct, a liquid is NOT a solid body. It is a LIQUID body hence the term liquid! Different fluids exhibit different properties. Water is not compressible. Air is. Air is also a fluid!
Why do you think sediment falls out of suspension from the water on the inside of a turn? Its because it is moving slowly! Slower moving water posseses far less energy with which to transport sediment. Water on the outside of a turn is moving much faster and this makes it far easier for sediment to stay in suspension. This faster moving water also picks up MORE sediment as it passes by. Velocity means everything. What do you think keeps things in orbit in space around this planet? The space station doesn't stay there because there is no gravity. At that altitude there is still about 95% of the gravity that we have here on the ground. It is the sheer velocity of the station that keeps it up there. The lack of atmosphere just removes the resistence to easily hold this momentum. You have to get almost 25000 miles away before gravity has little to no effect when you aren't moving. Maybe you don't realize that it only takes 6" of water to move a 3000 lb. car if the water is moving at least 20 mph. If your incorrect theory were applied here then the car would float away in non-moving water but stay still in rapidly moving water. Let me tell you a little about my education. I've had 2 years of geology, I've taken chemistry 1 and 2 (although it doesn't apply to this argument), physics, several acoustics classes, and fluid mechanics since my major is Mechanical Engineering not to mention all the other required classes I won't list. You can't BS ME!!! Your arguments make absolutely NO sense with any relation to physics in this universe or at least on this planet and I can only deduce that you came to these conclusions on your own. I don't need REALLY informative texts because I already have DEFINITE lab results from personal experience. When you can provide physical proof I'm wrong (and you can't!) then I'll go farther in this discussion.
Why do you think sediment falls out of suspension from the water on the inside of a turn? Its because it is moving slowly! Slower moving water posseses far less energy with which to transport sediment. Water on the outside of a turn is moving much faster and this makes it far easier for sediment to stay in suspension. This faster moving water also picks up MORE sediment as it passes by. Velocity means everything. What do you think keeps things in orbit in space around this planet? The space station doesn't stay there because there is no gravity. At that altitude there is still about 95% of the gravity that we have here on the ground. It is the sheer velocity of the station that keeps it up there. The lack of atmosphere just removes the resistence to easily hold this momentum. You have to get almost 25000 miles away before gravity has little to no effect when you aren't moving. Maybe you don't realize that it only takes 6" of water to move a 3000 lb. car if the water is moving at least 20 mph. If your incorrect theory were applied here then the car would float away in non-moving water but stay still in rapidly moving water. Let me tell you a little about my education. I've had 2 years of geology, I've taken chemistry 1 and 2 (although it doesn't apply to this argument), physics, several acoustics classes, and fluid mechanics since my major is Mechanical Engineering not to mention all the other required classes I won't list. You can't BS ME!!! Your arguments make absolutely NO sense with any relation to physics in this universe or at least on this planet and I can only deduce that you came to these conclusions on your own. I don't need REALLY informative texts because I already have DEFINITE lab results from personal experience. When you can provide physical proof I'm wrong (and you can't!) then I'll go farther in this discussion.
03-01-03, 03:04 AM
#17
Absolute Power is Awesome
Thanks for giving your credentials. I see why you are confused, they don't teach complex fliuds in undergrad classes.
i've got one up on you as I have a masters in mechanical engineering from the University of Wisconsin at the engine research center. I specifically studied fluid flow and combustion for two years and have been working in fluids for the past three years.
This is me,
http://www.erc.wisc.edu/wsec/former/rubenstein.html
(I'm really not that ugly!?!)
You can also look up my name at SAE.org to see my paper on port flow bench simulation.
I really don't mean to be confrontational, I'm just trying to be an informational part of this great forum.
i've got one up on you as I have a masters in mechanical engineering from the University of Wisconsin at the engine research center. I specifically studied fluid flow and combustion for two years and have been working in fluids for the past three years.
This is me,
http://www.erc.wisc.edu/wsec/former/rubenstein.html
(I'm really not that ugly!?!)
You can also look up my name at SAE.org to see my paper on port flow bench simulation.
I really don't mean to be confrontational, I'm just trying to be an informational part of this great forum.
Last edited by purple82; 03-01-03 at 03:24 AM.
03-01-03, 06:36 AM
#18
Airflow is my life
Purple, not saying your wrong cause you 2 guys are wayyyyyyyyy smarter than me. But..... doesnt the incompressibility of a liquid render the river analogy moot in this case? Also, I dont understand your explanation of velocity in the bend. It defies all logic. The outside is the highest velocity. Like an airplane wing. The air over the top has to travel further than the bottom, so velocity is higher on the top so the air can meet back up at the trailing edge. and consequently pressure on top goes down.
03-01-03, 07:08 AM
#19
Absolute Power is Awesome
I'm happy to explain. I totally understand that this is counter intuitive. It blows away just about everyone when they first learn this phenomenon. This may be a bit long, I'll try to condense as much as I can.
This secondary fluid motion that I've been talking about occurs on the surface of airplane wings as well because of the difference in airspeed between the base of the wing and the air at the tip.
The first thing you need to do is visualize fluid as a bunch of very small particles that move around relative to each other with a loose inter-bond between them. There is nothing that says two particles next to each other at one point in an airflow stream need to stay next to each other under changes in flow direction. This is the piece of the puzzle that helps to understand airflow behavior.
Imagine two particles in the air, one above the other. They are about to be split by a wing flowing through the air. When air is separated by the wing, the airstream across the top of the wing must move a longer distance than the air across the bottom. When the two streams re-attach (usually not very smoothly, but let's stay theoretical) the top particle will be behind the bottom. They will no longer be one on top of the other because the flow path of the two has been disturbed in different ways.
For a fluid going around a bend, don't think of one car going around a corner, think of ten cars going around a corner. Before coming to the corner, they are all nose to nose. As they round the corner, the inside cars will be ahead of the outside cars because they have a shorter distance to travel. At the exit of the corner, the inside cars will have a clear lead on the outside cars. This is similar to what happens with water in a river.
Incompressibility doesn't mean that the flow can't be separated, or move relative to itself. It just means that changes in density due to pressure can be ignored
The secondary flow that I refer to is an artifact of these differences in the speed of the fluid in the flow.
This secondary fluid motion that I've been talking about occurs on the surface of airplane wings as well because of the difference in airspeed between the base of the wing and the air at the tip.
The first thing you need to do is visualize fluid as a bunch of very small particles that move around relative to each other with a loose inter-bond between them. There is nothing that says two particles next to each other at one point in an airflow stream need to stay next to each other under changes in flow direction. This is the piece of the puzzle that helps to understand airflow behavior.
Imagine two particles in the air, one above the other. They are about to be split by a wing flowing through the air. When air is separated by the wing, the airstream across the top of the wing must move a longer distance than the air across the bottom. When the two streams re-attach (usually not very smoothly, but let's stay theoretical) the top particle will be behind the bottom. They will no longer be one on top of the other because the flow path of the two has been disturbed in different ways.
For a fluid going around a bend, don't think of one car going around a corner, think of ten cars going around a corner. Before coming to the corner, they are all nose to nose. As they round the corner, the inside cars will be ahead of the outside cars because they have a shorter distance to travel. At the exit of the corner, the inside cars will have a clear lead on the outside cars. This is similar to what happens with water in a river.
Incompressibility doesn't mean that the flow can't be separated, or move relative to itself. It just means that changes in density due to pressure can be ignored
The secondary flow that I refer to is an artifact of these differences in the speed of the fluid in the flow.
Last edited by purple82; 03-01-03 at 07:14 AM.
03-01-03, 08:38 AM
#22
Purple82, I was reading what you wrote, and I havent taken classes in any of this stuff, yet it seems to make sense. The only question I have is with your car around the corner analogy. Although this makes perfect sense, I dont understand how this relates to intake flow. When the cars go around the bend, they are on a guided path (the road, track, course, etc), and self guided around said path. The intake flow however, is not so much on a guided path, and is definatly not self guided. When it enters the plate, its just going for the path of least resistance, correct? I realize that would be the port into the combustion chamber, but that 90° corner straight ahead would be pretty inviting to head on collide with, dont you think? I mean, the engine is creating vaccum that should suck the intake in before its in limbo too long, but would a smoother flow straight into the engine at least help a little? So if when the intake is being pulled in, it can easily be pulled straight into the combustion chamer rather than creating a "low pressure" zone or whatever as you had called it in the corner of the 90° turn? So wouldnt that help a little? Even if not not to aleviate the amount of vaccum required to pull the intake into the combustion chamber? And if it did just that, then wouldnt that in theroy create more power because of less of a parasitic drag on the engine, even though it is a minute amount? I just dont understand how you can say that the pineapple sleeves do nothing when I have seen dyno charts that proove otherwise. Anyway, Im trying to keep up with this convo and learn, so please forgive me if this is an obviously stupid question 
.
~T.J.
.~T.J.
03-01-03, 09:12 AM
#23
Absolute Power is Awesome
The corner is actually high pressure, not low like I mentioned earlier, sorry about that.
When the port opens, there will be a pressure differential that forces the air into the combustion chamber. As the air wave comes down the port, it's going to create an air "wedge" in that corner, this is why I say the Pineapple sleeves aren't doing anything. If the sleeves are somehow improving the entrance of the flow into the chamber by adjusting the angle that the air enters (maybe more in line with the port?), there may be some improvement, but the air should take care of this itself. Like you said, it wants to take the path of least resistance.
Anyone have a cross secion of the Pineapple sleeve? I can do a quick CFD model on it if I know the angle of the ramp at the housing end and show it to you guys. I'd be interested in seeing the dyno numbers you're referring to.
When the port opens, there will be a pressure differential that forces the air into the combustion chamber. As the air wave comes down the port, it's going to create an air "wedge" in that corner, this is why I say the Pineapple sleeves aren't doing anything. If the sleeves are somehow improving the entrance of the flow into the chamber by adjusting the angle that the air enters (maybe more in line with the port?), there may be some improvement, but the air should take care of this itself. Like you said, it wants to take the path of least resistance.
Anyone have a cross secion of the Pineapple sleeve? I can do a quick CFD model on it if I know the angle of the ramp at the housing end and show it to you guys. I'd be interested in seeing the dyno numbers you're referring to.
03-01-03, 09:52 AM
#24
Anyone have a cross secion of the Pineapple sleeve? I can do a quick CFD model on it if I know the angle of the ramp at the housing end and show it to you guys.
I'd be interested in seeing the dyno numbers you're referring to.
.~T.J.
