The Myth: Resonance Tuning vs. BackPressure
Registered User
Joined: Feb 2004
Posts: 34
From: waterboro,Maine
Alright i'll admit, I'm not a genuis. That was difficult. I'm new here at this board and find this topic very interesting. Oh and I'm terrible at spelling please forgive me. Now i have a few words of input and a question.
I have read many of David Vizard's books so i have a basic understanding of how an exhaust system works or should work, even though i can't mathmatically back up my statements. From what i understand the "pulse" will not travel back up the pipe until it hits either a wall or the atmosphere. the collector actually helps scavange more exhaust out; actually adding to the collector scavanges more, usually around 18" longer. the pulse bounces off the atmospheric pressure it see's at the end of the pipe(14.7 lbs). most of us can only tune off the third pulse(wave) because it happens so fast, and we have to deal with the confines of the car. you can get rid of the wave tunning buy building a "big can" at the precise point of the end of the collector. There is a formula, the can must be at least 8 times the volume of one cylinder but would be better if it were 11-15 the size. after this all you have to deal with is no back pressure. this can would make the engine think its running on open headers with a correct length collector. the can is so big that it acts like a big shock absorber(thats how i think of it.
I have trouble believing that the collector will cause a pressure wave to bounce back up the primary tube. only until the pulse hit atmospheric pressure or the end of the collector. in my understanding a wave will bounce off at the same angle it arrived at the object. so unless you have some really funky header collectors i don't see how it could happen. But like i said earlier i'm not a genius and i don't have any degrees in any type of wave dynamics so i may be way off base here.
The question i have is this: is it posible to have any type of scavanging with headers and a single exhaust that would fit under a 3rd Gen.? If so is there a muffler that will flow 950CFM with one pipe in and out.
I think i'm better off just making a custom exhaust. i'm using Super Comp long tube headers. I have a 400 sm blk making around 390-410 HP with a cam of 106 lobe seperation to use exhaust scavanging to help with the mid range and top end.
Thanks.
I have read many of David Vizard's books so i have a basic understanding of how an exhaust system works or should work, even though i can't mathmatically back up my statements. From what i understand the "pulse" will not travel back up the pipe until it hits either a wall or the atmosphere. the collector actually helps scavange more exhaust out; actually adding to the collector scavanges more, usually around 18" longer. the pulse bounces off the atmospheric pressure it see's at the end of the pipe(14.7 lbs). most of us can only tune off the third pulse(wave) because it happens so fast, and we have to deal with the confines of the car. you can get rid of the wave tunning buy building a "big can" at the precise point of the end of the collector. There is a formula, the can must be at least 8 times the volume of one cylinder but would be better if it were 11-15 the size. after this all you have to deal with is no back pressure. this can would make the engine think its running on open headers with a correct length collector. the can is so big that it acts like a big shock absorber(thats how i think of it.
I have trouble believing that the collector will cause a pressure wave to bounce back up the primary tube. only until the pulse hit atmospheric pressure or the end of the collector. in my understanding a wave will bounce off at the same angle it arrived at the object. so unless you have some really funky header collectors i don't see how it could happen. But like i said earlier i'm not a genius and i don't have any degrees in any type of wave dynamics so i may be way off base here.
The question i have is this: is it posible to have any type of scavanging with headers and a single exhaust that would fit under a 3rd Gen.? If so is there a muffler that will flow 950CFM with one pipe in and out.
I think i'm better off just making a custom exhaust. i'm using Super Comp long tube headers. I have a 400 sm blk making around 390-410 HP with a cam of 106 lobe seperation to use exhaust scavanging to help with the mid range and top end.
Thanks.
Thread Starter
Registered User
Joined: Sep 2002
Posts: 655
The short answer would be yes, there is scavening in a single
pipe exhaust system.
As the gas velocity builds at higher RPM, the system pressure lowers
allowing for intake charge to fill the "void".
I would suggest something like a Warlock muffler made by Flowtech.
Their numbers are pretty good. I don't recall the flow numbers
off hand, but I recall the Warlock series being high up on the list.
If you read this entire thread, you'll find answers to most of your
concerns and maybe more insight on your question.
If anyone can confirm my post at the end of the 3rd page regarding
chapters in the book, "Scientific Design of Exhaust and Intake Systems"
it would be really cool!
pipe exhaust system.
As the gas velocity builds at higher RPM, the system pressure lowers
allowing for intake charge to fill the "void".
I would suggest something like a Warlock muffler made by Flowtech.
Their numbers are pretty good. I don't recall the flow numbers
off hand, but I recall the Warlock series being high up on the list.
If you read this entire thread, you'll find answers to most of your
concerns and maybe more insight on your question.
If anyone can confirm my post at the end of the 3rd page regarding
chapters in the book, "Scientific Design of Exhaust and Intake Systems"
it would be really cool!
Registered User
Joined: Feb 2004
Posts: 34
From: waterboro,Maine
Thanks.
check out this link, its by David Vizard, so everybody can see.
http://www.geocities.com/MotorCity/T...92/vizard.html
check out this link, its by David Vizard, so everybody can see.
http://www.geocities.com/MotorCity/T...92/vizard.html
Registered User
Joined: Feb 2004
Posts: 34
From: waterboro,Maine
i read your 3rd page post . i think the VE will still be up but your fuel milage will go down. i can't off the top of my head remember what its called on the dyno, something like, Brake Specific Fuel Consumption. basically it tells you how much fuel your using to make the power and it lets you know how much you could be wasting. But the engine itself sees that the VE is up because there is no exhaust left in the chamber. when you run a super charger you should be running cam with between 112-118 LSA depending on duration to help offset this problem. thats part of what makes a blower/NOS cam what it is.
Registered User
Joined: Oct 2002
Posts: 2,931
From: Upstate NY
Originally posted by 408TA
I have read many of David Vizard's books so i have a basic understanding of how an exhaust system works or should work, even though i can't mathmatically back up my statements. From what i understand the "pulse" will not travel back up the pipe until it hits either a wall or the atmosphere.
Maybe it's not as rigid as that. Any abrupt change, like an intersection with another pipe, a step, or a large enough volume change can cause a reflection.
the collector actually helps scavange more exhaust out; actually adding to the collector scavanges more, usually around 18" longer. the pulse bounces off the atmospheric pressure it see's at the end of the pipe(14.7 lbs). most of us can only tune off the third pulse(wave) because it happens so fast, and we have to deal with the confines of the car.
Optimum collector length probably varies with your engine combination, but 15-18 inches is right in there for many engines.
you can get rid of the wave tunning buy building a "big can" at the precise point of the end of the collector. There is a formula, the can must be at least 8 times the volume of one cylinder but would be better if it were 11-15 the size. after this all you have to deal with is no back pressure. this can would make the engine think its running on open headers with a correct length collector. the can is so big that it acts like a big shock absorber(thats how i think of it.
Yes, "Terminator boxes" can be effective. The exhaust thinks of the box as "all outdoors". There are probably other ways to achieve this and still have a complete exhaust system. The Brooklands Silencer or "receiver" of the early 1920s(!) was, in effect, a terminator box. I think of them as a way to fool the exhaust into thinking it ends at the collector. I'm a big fan of these, and have built a few.
I have trouble believing that the collector will cause a pressure wave to bounce back up the primary tube. only until the pulse hit atmospheric pressure or the end of the collector. in my understanding a wave will bounce off at the same angle it arrived at the object. so unless you have some really funky header collectors i don't see how it could happen. But like i said earlier i'm not a genius and i don't have any degrees in any type of wave dynamics so i may be way off base here.
Remember, the pulse doesn't need a "wall", just a change of volume. Collectors can cause this.
The question i have is this: is it posible to have any type of scavanging with headers and a single exhaust that would fit under a 3rd Gen.? If so is there a muffler that will flow 950CFM with one pipe in and out.
How about a couple of terminator boxes and then a "Y" behind them? There are some Dynomax Ultraflow Welded 3 inch mufflers that flow twice than. Magnaflow clones of them do, too.
I think i'm better off just making a custom exhaust. i'm using Super Comp long tube headers. I have a 400 sm blk making around 390-410 HP with a cam of 106 lobe seperation to use exhaust scavanging to help with the mid range and top end.
Thanks.
No comment on your cam, but the custom exhaust makes sense to me. Good luck.
I have read many of David Vizard's books so i have a basic understanding of how an exhaust system works or should work, even though i can't mathmatically back up my statements. From what i understand the "pulse" will not travel back up the pipe until it hits either a wall or the atmosphere.
Maybe it's not as rigid as that. Any abrupt change, like an intersection with another pipe, a step, or a large enough volume change can cause a reflection.
the collector actually helps scavange more exhaust out; actually adding to the collector scavanges more, usually around 18" longer. the pulse bounces off the atmospheric pressure it see's at the end of the pipe(14.7 lbs). most of us can only tune off the third pulse(wave) because it happens so fast, and we have to deal with the confines of the car.
Optimum collector length probably varies with your engine combination, but 15-18 inches is right in there for many engines.
you can get rid of the wave tunning buy building a "big can" at the precise point of the end of the collector. There is a formula, the can must be at least 8 times the volume of one cylinder but would be better if it were 11-15 the size. after this all you have to deal with is no back pressure. this can would make the engine think its running on open headers with a correct length collector. the can is so big that it acts like a big shock absorber(thats how i think of it.
Yes, "Terminator boxes" can be effective. The exhaust thinks of the box as "all outdoors". There are probably other ways to achieve this and still have a complete exhaust system. The Brooklands Silencer or "receiver" of the early 1920s(!) was, in effect, a terminator box. I think of them as a way to fool the exhaust into thinking it ends at the collector. I'm a big fan of these, and have built a few.
I have trouble believing that the collector will cause a pressure wave to bounce back up the primary tube. only until the pulse hit atmospheric pressure or the end of the collector. in my understanding a wave will bounce off at the same angle it arrived at the object. so unless you have some really funky header collectors i don't see how it could happen. But like i said earlier i'm not a genius and i don't have any degrees in any type of wave dynamics so i may be way off base here.
Remember, the pulse doesn't need a "wall", just a change of volume. Collectors can cause this.
The question i have is this: is it posible to have any type of scavanging with headers and a single exhaust that would fit under a 3rd Gen.? If so is there a muffler that will flow 950CFM with one pipe in and out.
How about a couple of terminator boxes and then a "Y" behind them? There are some Dynomax Ultraflow Welded 3 inch mufflers that flow twice than. Magnaflow clones of them do, too.
I think i'm better off just making a custom exhaust. i'm using Super Comp long tube headers. I have a 400 sm blk making around 390-410 HP with a cam of 106 lobe seperation to use exhaust scavanging to help with the mid range and top end.
Thanks.
No comment on your cam, but the custom exhaust makes sense to me. Good luck.
Registered User
Joined: Feb 2004
Posts: 34
From: waterboro,Maine
Remember, the pulse doesn't need a "wall", just a change of volume. Collectors can cause this.
How would this explain how stepped race headers work. I was under the impression that each step did 2 things, 1 help with reversion, 2 keep the gases moving fast in one direction for higher RPM use, therefore broadening the power band.
i still don't understand how 4 pipes in parallel dumping into a properly fit collector will cause a wave back up the primary. i could see it changing shape and speed on the way out of the collector.
i would think that if the collector sent a wave back up the primaries as soon as the primaries dumped their charge in them then running no collector at all wouldn't change the performance charateristics. But all "naturally" aspirated sm blk chevys will produce more power and torque with a collector then with out. you can not physically fit a long enough primary into a vehicle for wave tuning with out a collector.Grouping all 4 primaries together produces a very strong wave/vacuum to tune with, unfortunately 1 cylinder on each bank for a sm blk chevy is out of sequence. but i guess 3 out of 4 isn't bad. this is where the afterburner by flow tech comes into play they put the out of sequence cylinder kind out of play by introducing it at a right angle so it doesn't interfere with the wave tuning as much. it sounds good anyways.
blowers motors don't need collectors because they don't have to rely on scavanging to completly clear out the combustion chamber. the forces produced by the blower out way any affect the exhaust scavanging would have, this is of course for a race purpose vehicle. How many top fuelers have them? how many ProStockers have them?
i'm not triing to be a smart "butt" , but just looking for some answers for us all.
I'm using the engine in a 88TA for the street, therefore i really don't have much room to put in the terminator boxes not to mention triing to work around the subframe connectors. the mufflers need to be streetable.
the cam is nothing special, just a Comp 270H ground on a 106 LSA installed at 102.
How would this explain how stepped race headers work. I was under the impression that each step did 2 things, 1 help with reversion, 2 keep the gases moving fast in one direction for higher RPM use, therefore broadening the power band.
i still don't understand how 4 pipes in parallel dumping into a properly fit collector will cause a wave back up the primary. i could see it changing shape and speed on the way out of the collector.
i would think that if the collector sent a wave back up the primaries as soon as the primaries dumped their charge in them then running no collector at all wouldn't change the performance charateristics. But all "naturally" aspirated sm blk chevys will produce more power and torque with a collector then with out. you can not physically fit a long enough primary into a vehicle for wave tuning with out a collector.Grouping all 4 primaries together produces a very strong wave/vacuum to tune with, unfortunately 1 cylinder on each bank for a sm blk chevy is out of sequence. but i guess 3 out of 4 isn't bad. this is where the afterburner by flow tech comes into play they put the out of sequence cylinder kind out of play by introducing it at a right angle so it doesn't interfere with the wave tuning as much. it sounds good anyways.
blowers motors don't need collectors because they don't have to rely on scavanging to completly clear out the combustion chamber. the forces produced by the blower out way any affect the exhaust scavanging would have, this is of course for a race purpose vehicle. How many top fuelers have them? how many ProStockers have them?
i'm not triing to be a smart "butt" , but just looking for some answers for us all.
I'm using the engine in a 88TA for the street, therefore i really don't have much room to put in the terminator boxes not to mention triing to work around the subframe connectors. the mufflers need to be streetable.
the cam is nothing special, just a Comp 270H ground on a 106 LSA installed at 102.
Last edited by 408TA; Feb 16, 2004 at 07:48 PM.
Thread Starter
Registered User
Joined: Sep 2002
Posts: 655
Just a word of caution:
I tried proving some of these guys wrong...I was sent to the corner
without dinner for a week.
I had the same questions you have, and after dipping into this
book, I can understand how very little I actually know about engines.
I used to think I was a 7 out of 10 when talking about engine
tuning. Now, it's more like -7!
Stick around, you're going to love talking with these people.
Keep an eye out for Damon, KmooK, Old SS, Injuneer, MaxRace,
R. Kraus (sorry if I forgot any other regulars!)
My questions are still somewhat unanswered - last post on page 3!!!
I tried proving some of these guys wrong...I was sent to the corner
without dinner for a week.
I had the same questions you have, and after dipping into this
book, I can understand how very little I actually know about engines.
I used to think I was a 7 out of 10 when talking about engine
tuning. Now, it's more like -7!
Stick around, you're going to love talking with these people.
Keep an eye out for Damon, KmooK, Old SS, Injuneer, MaxRace,
R. Kraus (sorry if I forgot any other regulars!)
My questions are still somewhat unanswered - last post on page 3!!!
Registered User
Joined: Feb 2004
Posts: 34
From: waterboro,Maine
i have a low tech idea i will try. i will fill the sink full of water and simulate a header and collector, then make a wave in the "primary" tube and see what happens. i know its water but the "waves" may help to visualize it for me!
Registered User
Joined: Oct 2002
Posts: 2,931
From: Upstate NY
The steps to larger diameter slow down the velocity of the gasses. I'm not sure how that "keeps the gasses moving fast in one direction." The steps are there, AFAIK, to initiate a pressure wave reflection.
I think if it as two distinct things in exhaust systems: physical flow of the gas away from the cylinders, and pressure waves travelling both ways in the flow. Average velocity of the flow increases with rpm to maybe 400 ft/sec. The pressure or tuning waves are sonic, or about 1300-1400 ft/sec, depending on exhaust temp. Even at room temp, sonic velocity is about 1100 ft/sec. The resonance tuning involves the fast sonic waves, or actually changes of pressure. These are superimposed on the actual flow of the exhaust gas.
Reversion is backflow of the gasses, not pressure pulses. I believe you can help minimize reversion by having the primary pipe larger than the exhaust port. The gas which is tryng to reverse its flow back into the cylinder during ovelap bounces off the "wall" as it hits the exhaust port. Flow outward isn't hindered going from a smaller pipe, the exhaust port, to a larger one, the header. Putting the mismatch in the lowest flow area of the port is probably wise.
I think if it as two distinct things in exhaust systems: physical flow of the gas away from the cylinders, and pressure waves travelling both ways in the flow. Average velocity of the flow increases with rpm to maybe 400 ft/sec. The pressure or tuning waves are sonic, or about 1300-1400 ft/sec, depending on exhaust temp. Even at room temp, sonic velocity is about 1100 ft/sec. The resonance tuning involves the fast sonic waves, or actually changes of pressure. These are superimposed on the actual flow of the exhaust gas.
Reversion is backflow of the gasses, not pressure pulses. I believe you can help minimize reversion by having the primary pipe larger than the exhaust port. The gas which is tryng to reverse its flow back into the cylinder during ovelap bounces off the "wall" as it hits the exhaust port. Flow outward isn't hindered going from a smaller pipe, the exhaust port, to a larger one, the header. Putting the mismatch in the lowest flow area of the port is probably wise.
Registered User
Joined: Oct 2002
Posts: 2,931
From: Upstate NY
Originally posted by Zero_to_69
OK, here come the questions! I', not quite finished the first chapter
yet, but I want to make sure I'm grasping the terms before moving
on too far.
1. "Gasification" means to change the fuel from its liquid state to
a gas state, correct?
Yes.
All I'm thinking is atomization at this point.
Is there more to this such as "conditioning" the intake charge?
Atomization means separating something into fine particles, which are probably liquid droplets in the inlet manifold, not a gas.
2. Risidual exhaust gas in the chamber after the exhaust stroke is completed, heats up the intake charge and displaces volume for the intake charge. This is more apparent at low RPM because exhuast gas velocity is not high enough to scavenge the cylinder as the exhaust manifold dimensions are also not tuned for this range. This residual effect acts very similar to an EGR circuit.
Sounds good.
The question is about Thermal Efficiency. Is this referring to optimal chamber temperatures for combustion, or quality of the intake charge?
Neither. TE is a term that describes how efficiently the combustion and expansion process makes use of the heat energy which pushes on the piston during the expansion stroke. Think of it as the heat left in the exhaust gasses. Higher TE would mean lower exhaust gas temp because more of the heat was used pushing down the piston. Typical TE's are 25-35%, and 40% probably the best you could hope to achieve. Plagerized from Performance Trends, Inc.
3. Blowdown when using a supercharger: This causes fresh intake charge to over-shoot the chamber and enter the exhaust manifold. The higher inlet pressure allows for total scavenge of the combustion chamber which is beneficial for the power stroke torque production.
My question is...will the charge 'over-shooting' the chamber reduce volumetric efficiency, or is there enough charge coming in that a sufficient amount will be trapped?
I think I just answered my own question...but he talks as if it's a
good thing that fresh charge is wasted. I guess it's a "Give and
Take" trade off (VE% vs. full scavenge)?
Extreme example might be Top Fuel engines where the blowing-down is so severe that nitromethane which is blown thru burns in the exhaust pipes creating the 10 feet or so of flames and maybe a thousand or more pounds of down force. My guess is that when they lose a cylinder or two on one side, the horizontal component of this "Zoomie Force" steers the car!
OK, here come the questions! I', not quite finished the first chapter
yet, but I want to make sure I'm grasping the terms before moving
on too far.
1. "Gasification" means to change the fuel from its liquid state to
a gas state, correct?
Yes.
All I'm thinking is atomization at this point.
Is there more to this such as "conditioning" the intake charge?
Atomization means separating something into fine particles, which are probably liquid droplets in the inlet manifold, not a gas.
2. Risidual exhaust gas in the chamber after the exhaust stroke is completed, heats up the intake charge and displaces volume for the intake charge. This is more apparent at low RPM because exhuast gas velocity is not high enough to scavenge the cylinder as the exhaust manifold dimensions are also not tuned for this range. This residual effect acts very similar to an EGR circuit.
Sounds good.
The question is about Thermal Efficiency. Is this referring to optimal chamber temperatures for combustion, or quality of the intake charge?
Neither. TE is a term that describes how efficiently the combustion and expansion process makes use of the heat energy which pushes on the piston during the expansion stroke. Think of it as the heat left in the exhaust gasses. Higher TE would mean lower exhaust gas temp because more of the heat was used pushing down the piston. Typical TE's are 25-35%, and 40% probably the best you could hope to achieve. Plagerized from Performance Trends, Inc.
3. Blowdown when using a supercharger: This causes fresh intake charge to over-shoot the chamber and enter the exhaust manifold. The higher inlet pressure allows for total scavenge of the combustion chamber which is beneficial for the power stroke torque production.
My question is...will the charge 'over-shooting' the chamber reduce volumetric efficiency, or is there enough charge coming in that a sufficient amount will be trapped?
I think I just answered my own question...but he talks as if it's a
good thing that fresh charge is wasted. I guess it's a "Give and
Take" trade off (VE% vs. full scavenge)?
Extreme example might be Top Fuel engines where the blowing-down is so severe that nitromethane which is blown thru burns in the exhaust pipes creating the 10 feet or so of flames and maybe a thousand or more pounds of down force. My guess is that when they lose a cylinder or two on one side, the horizontal component of this "Zoomie Force" steers the car!
Registered User
Joined: Feb 2004
Posts: 34
From: waterboro,Maine
Alright, alright. i'll go pick up the book, Damn! the biggest reason i don't want to read the book is beacuse if it has those "big" words in it(you know like the ones the politicians use), then i'll be reading the dictionary more than the book!!!!!!!!!!
i can grasp the reversion part, its just that darn sonic thing!
pretty much though from what i've heard it would be very hard in a street car to tune with sonic waves..... correct? if so then I(we) should work more on how to get those terminator boxes under our cars so it doesn't affect any of our tunning.
PS: unfortunatly my wife was rite; i don't know everything!
i can grasp the reversion part, its just that darn sonic thing!
pretty much though from what i've heard it would be very hard in a street car to tune with sonic waves..... correct? if so then I(we) should work more on how to get those terminator boxes under our cars so it doesn't affect any of our tunning.
PS: unfortunatly my wife was rite; i don't know everything!
Last edited by 408TA; Feb 17, 2004 at 06:59 AM.
Registered User
Joined: Feb 2004
Posts: 34
From: waterboro,Maine
Registered User
Joined: Feb 2004
Posts: 291
From: Abbeville , LA
there's an error in that article =>"Backpressure"
its an incorrect view
not at all the same theory as "Scientific Design of Intake and Exhaust Systems"
Backpressure will cause Torque/HP Loss 99 percent of time
its an incorrect view
not at all the same theory as "Scientific Design of Intake and Exhaust Systems"
Backpressure will cause Torque/HP Loss 99 percent of time
Registered User
Joined: Feb 2004
Posts: 291
From: Abbeville , LA
It is true that some engines are mechanically tuned to a certain amount of backpressure and can show a loss of low-end torque when that backpressure is reduced.
--------------------------------------------------------------------------
the above statement is in error, the rest of article is very good and accurate
its not the "backpressure" helping in that statement , but the opposite > its "the TIMING" of the "negative" acoustical wave responsible for TQ/HP improvement
the loss in low-end torque is because there is no negative wave at overlap period occuring
--------------------------------------------------------------------------
the above statement is in error, the rest of article is very good and accurate
its not the "backpressure" helping in that statement , but the opposite > its "the TIMING" of the "negative" acoustical wave responsible for TQ/HP improvement
the loss in low-end torque is because there is no negative wave at overlap period occuring