OK...Back Pressure Shoot out! One and for all!
11-11-2003, 09:38 AM
#31
Registered User
Join Date: Dec 2002
Posts: 165
Likes: 0
Received 0 Likes
on
0 Posts
Re:OK...Back Pressure Shoot out! One and for all!
[quote author=Willyzao link=board=7;threadid=22079;start=15#msg207140 date=1068249386]
[quote author=Diesel Freak link=board=7;threadid=22079;start=15#msg207132 date=1068248137]
they are blatantly stating that the gases are "working on themselves without any external energy input" to raise their velocity.
to accelerate a gas, a convergent nozzle is employed, and this ends up being a flow restriction which raises upstream pressure in the system.
They are trying to sell perpetual motion, a clear violation of the conservation of energy principle.[/quote]
I'll give you that, that's a much better argument. You and Don M sound like good guys to have around the campfire when it's time to start philosophizing. Is that Don M of Don M's EDM injectors? Just curious.
[/quote]
Yes that is the infamous Don Morrison.
I can philosophize great around a camp fire.....even better when I have a few beers
[quote author=Diesel Freak link=board=7;threadid=22079;start=15#msg207132 date=1068248137]
they are blatantly stating that the gases are "working on themselves without any external energy input" to raise their velocity.
to accelerate a gas, a convergent nozzle is employed, and this ends up being a flow restriction which raises upstream pressure in the system.
They are trying to sell perpetual motion, a clear violation of the conservation of energy principle.[/quote]
I'll give you that, that's a much better argument. You and Don M sound like good guys to have around the campfire when it's time to start philosophizing. Is that Don M of Don M's EDM injectors? Just curious.
[/quote]
Yes that is the infamous Don Morrison.
I can philosophize great around a camp fire.....even better when I have a few beers
11-11-2003, 10:10 AM
#32
DTR Advertiser
Re:OK...Back Pressure Shoot out! One and for all!
Anyone know about the testing that Smokey Yunick did back in the day? He was working on a venturi system for the exhaust systems in NASCAR. He also tested for months on the placement of the exhaust pipe outlet under the car. He probed around and measured the absolute lowest pressure area he could find and placed the outlet in that area. His words were....that you could gain a tremendous amount of HP , he said it was almost like installing a supercharger. Not sure how much he was exaggerating the point, but he was not known for exaggeration!
How about the trick where he drilled holes in the header tubes just after they left the cylinder head. The gasses passing through the headers pulled in air from the outside and with the correct cam timing would raise the temps in the headers from feeding the unburned fuel with fresh oxygen. Velocity increased!
Of course NASCAR climbed all over the car that day and made them illegal on the spot
Really the holes did not pull in air..the air was of course under ambient pressure of 14 PSI or so.
Thats another point he was trying to make with the placement of the exhaust in the low pressure area. The ambient air is actually under 14 or so PSI...it takes work to push the exhaust out of the pipe into a pressurized environment like we live in.
Don~
How about the trick where he drilled holes in the header tubes just after they left the cylinder head. The gasses passing through the headers pulled in air from the outside and with the correct cam timing would raise the temps in the headers from feeding the unburned fuel with fresh oxygen. Velocity increased!
Of course NASCAR climbed all over the car that day and made them illegal on the spot
Really the holes did not pull in air..the air was of course under ambient pressure of 14 PSI or so.
Thats another point he was trying to make with the placement of the exhaust in the low pressure area. The ambient air is actually under 14 or so PSI...it takes work to push the exhaust out of the pipe into a pressurized environment like we live in.
Don~
11-11-2003, 01:08 PM
#33
Registered User
Thread Starter
Join Date: Sep 2003
Location: Plano, TX
Posts: 2,534
Likes: 0
Received 0 Likes
on
0 Posts
Re:OK...Back Pressure Shoot out! One and for all!
Great posts!! I have learned soo much and lots of new words to use in everyday conversations! haha...anyway....this is why i had the questions i did...check this out...this is a quote from the Magnaflow web site from a PSR article:
The Turtle V was then moved to the prototype department where Richie took over. A master welder and fabricator by any scale, he explained that it is important to have the proper back pressure on the stock Power Stroke's turbo to allow it to spool up quickly for maximum boost and torque off the line. To this end, MagnaFlow uses a 3 1/2" down-tube before blending it into the full 4" system. Here is the link: http://www.magnaflow.com/05news/magazine/05psr.htm
Also, i have another question for yall. What happens when you put dual pipes on the truck? How does that effect the out come of the exhaust? We dualed out my Bosses Ford and it ran better than the single 4". here is my guess why from the before posts. The exhaust is going good in the 4" pipe until it hits the dual 3" pipes. Once it hits those, the velocity increases and thus reducing back pressure??? We did notice that when we installed Gibsons Dual Extreme on his PSD, it did make a noticeable increase in power over the 4” single out we had. Granted that we did have a 4” down pipe, but now wonder what the 3.5” would do for it now….but we are running LOTS of power through it! Thoughts?
Also, why do muffler manufacturers put the baffles in the muffler in a spiral pattern? Is it to spin the flow of the exhaust to increase the velocity? But I thought that spinning would hinder rather than help. If that is the case, why do the Helix Power Towers from Street and Performance, and the Air Raid Poweraid spacers do soo much good? The concept is to spin the air right before it enters the intake on the motor? I have felt a difference with the product and have seen dyno numbers to back it up. Cant the same with exhaust be done? Hence the spiral pattern on the baffles on the mufflers? Because even with a funnel full of water, it will empty faster with a spin rather than not. And that doent not have any air restrictions to hold the water back. Thoughts? (thought this topic could use more ether!)
The Turtle V was then moved to the prototype department where Richie took over. A master welder and fabricator by any scale, he explained that it is important to have the proper back pressure on the stock Power Stroke's turbo to allow it to spool up quickly for maximum boost and torque off the line. To this end, MagnaFlow uses a 3 1/2" down-tube before blending it into the full 4" system. Here is the link: http://www.magnaflow.com/05news/magazine/05psr.htm
Also, i have another question for yall. What happens when you put dual pipes on the truck? How does that effect the out come of the exhaust? We dualed out my Bosses Ford and it ran better than the single 4". here is my guess why from the before posts. The exhaust is going good in the 4" pipe until it hits the dual 3" pipes. Once it hits those, the velocity increases and thus reducing back pressure??? We did notice that when we installed Gibsons Dual Extreme on his PSD, it did make a noticeable increase in power over the 4” single out we had. Granted that we did have a 4” down pipe, but now wonder what the 3.5” would do for it now….but we are running LOTS of power through it! Thoughts?
Also, why do muffler manufacturers put the baffles in the muffler in a spiral pattern? Is it to spin the flow of the exhaust to increase the velocity? But I thought that spinning would hinder rather than help. If that is the case, why do the Helix Power Towers from Street and Performance, and the Air Raid Poweraid spacers do soo much good? The concept is to spin the air right before it enters the intake on the motor? I have felt a difference with the product and have seen dyno numbers to back it up. Cant the same with exhaust be done? Hence the spiral pattern on the baffles on the mufflers? Because even with a funnel full of water, it will empty faster with a spin rather than not. And that doent not have any air restrictions to hold the water back. Thoughts? (thought this topic could use more ether!)
11-11-2003, 02:12 PM
#34
Registered User
Join Date: Dec 2002
Posts: 165
Likes: 0
Received 0 Likes
on
0 Posts
Re:OK...Back Pressure Shoot out! One and for all!
I have dual exhaust on my truck. I went from single 4" to dual three inch. It is split using a Flowmaster 4" to dual 3" "Y" collector.
actually going from single 4" to dual 3" slows gas velocity slightly due to the larger flow area of two three inch pipes over a single 4" pipe.
Spiral baffles just serve th muffle the sound a little more than straight perforated core mufflers.
oh, and gasser intake mods dont work that well on a Diesel....
actually going from single 4" to dual 3" slows gas velocity slightly due to the larger flow area of two three inch pipes over a single 4" pipe.
Spiral baffles just serve th muffle the sound a little more than straight perforated core mufflers.
oh, and gasser intake mods dont work that well on a Diesel....
11-11-2003, 03:04 PM
#35
Registered User
Thread Starter
Join Date: Sep 2003
Location: Plano, TX
Posts: 2,534
Likes: 0
Received 0 Likes
on
0 Posts
Re:OK...Back Pressure Shoot out! One and for all!
Now why wouldn’t the theory of a Helix Spacer work all that well on a Diesel? I see it working better due to the fact that there is no throttle plate to restrict the flow of air. It is working 100% of the time. And I would hope that these people have done extensive testing on this product on the Dyno and other wise or they would not be asking about $100 for each! Talk about law suits! Now why wont the principle work? I like asking WHY! I learn more that way! haha....
ALSO notice that i have not mentioned the Tornado...I consider that snake oil and don’t think its worth mentioning. We have tried one first hand and have not see the results as the Helix.
ALSO notice that i have not mentioned the Tornado...I consider that snake oil and don’t think its worth mentioning. We have tried one first hand and have not see the results as the Helix.
11-11-2003, 03:05 PM
#36
Registered User
Join Date: Apr 2003
Location: Cummins Technical Center, IN
Posts: 6,564
Likes: 0
Received 6 Likes
on
5 Posts
Re:OK...Back Pressure Shoot out! One and for all!
The "proper" amount of back pressure is the amount that will generate the highest velocity for a given amount of axhaust restriction.
Back pressure in and of itself is NEVER good. But it DOES bring with it something that IS good-- higher velocity.
For example, if you take a certain amount of airflow and ducted it through a 5" pipe, you would measure a certain velocity and a certain amount of restriction (i.e. how much pressure it takes to flow that CFM). Now take that same amount and run it through a 4" pipe-- you have higher velocity, and it takes a hair more pressure to force that same CFM of airflow through. Repeat with progressively smaller and smaller pipes.
Eventually, you will get to the point where you simply cannot force the same amount of CFM through the pipe, no matter how much pressure you use to force it. The airflow through a given orifice (if graphed) will asymptotically approach a finite theoretical limit.
You can see this when you let air out of your tires. The air flows through the tire valve a lot faster at 80psi than it does at 30psi. But would you have double the airflow at 80psi than you do at 40psi? Not quite, though it may be close. Now what if you had 160psi? Would the airflow out of the tire be double of what you had at 80psi? Nope- this time it's not even as close to double. How about 320 psi? 640psi? 1280psi? Each time we double the pressure, we get even LESS increase in airflow. The first time we might get close to double. The next time we might get 1.8. Then maybe 1.4. Then maybe 1.1. Eventually, we hit a point where we cannot increase the airflow out of the tire, no matter how high we raise the pressure in it.
So we can see that increases in pressure and increases in flow are not in a 1:1 ratio. The opposite is also true. If we double an orifice size, the effective area increase is quite a bit more than double-- it's FOUR TIMES the first amount. A 4" exhaust has 33% more diameter than a 3"-- but it has (7.06"^2 vs 12.56"^2) 44% more area.
What we have then is a ratio. There is a certain velocity associated with a certain back pressure in this ratio. We optimize this ratio be comparing the velocity to back pressure of different pipe sizes. For example, if we found that going from a 3" exhaust to a 4" gave us 30% less backpressure, but dropped our velocity by 50%, then we could probably say that we have taken a step backwards. A 5" exhaust in this case would make things even worse.
But what if we had a BOMBed diesel engine? in this case, a switch from a 3" exhaust to a 4" exhaust might yield 40%-50% less backpressure, but only a 10% decrease in velocity. In this case, the 4" exhaust would DEFINITELY be an upgrade that's worthwhile.
I believe the optimum exhaust diameter to be that point where the ratio goes from favoring velocity to favoring backpressure. The diameter of the exhaust at this "crossover point" will vary from one engine to another depending on how much air the engine is capable of putting into the exhaust. A Stock CTD running 20PSI of boost has a lot less airflow than a BOMBED CTD that's running 45psi.
So we can see that backpressure in and of itself may be good or bad, depending on which side of the ratio you are on. For the PSD in the article above, the stock system was just a little too small, thus the increase in hp when the new exhaust was installed.
Also, the reason the 3.5 inch downpipe is maintained is not because the engine "needs" the "proper backpressure". It is because the engine needs to have the highest velocity for a given restriction, and a sudden transition to a 4" pipe straight out of the turbo will cause a sudden expansion that slows and cools the flow.
If the PSD is equipped with a 4" tubine outlet, the the 4" downpipe would be better.
One last thought on this novel-- The "optimum" exhaust for a given engine only exist for a certain condition of fueling, boost, and rpm. So that exhaust that seems to be "perfect" at peak rpm hp is costing you engine performance at every rpm above and beneath that.
Because of their nature as machines always in transition, engines are nothing but compromises of compromises.
WHEW!
Justin
Back pressure in and of itself is NEVER good. But it DOES bring with it something that IS good-- higher velocity.
For example, if you take a certain amount of airflow and ducted it through a 5" pipe, you would measure a certain velocity and a certain amount of restriction (i.e. how much pressure it takes to flow that CFM). Now take that same amount and run it through a 4" pipe-- you have higher velocity, and it takes a hair more pressure to force that same CFM of airflow through. Repeat with progressively smaller and smaller pipes.
Eventually, you will get to the point where you simply cannot force the same amount of CFM through the pipe, no matter how much pressure you use to force it. The airflow through a given orifice (if graphed) will asymptotically approach a finite theoretical limit.
You can see this when you let air out of your tires. The air flows through the tire valve a lot faster at 80psi than it does at 30psi. But would you have double the airflow at 80psi than you do at 40psi? Not quite, though it may be close. Now what if you had 160psi? Would the airflow out of the tire be double of what you had at 80psi? Nope- this time it's not even as close to double. How about 320 psi? 640psi? 1280psi? Each time we double the pressure, we get even LESS increase in airflow. The first time we might get close to double. The next time we might get 1.8. Then maybe 1.4. Then maybe 1.1. Eventually, we hit a point where we cannot increase the airflow out of the tire, no matter how high we raise the pressure in it.
So we can see that increases in pressure and increases in flow are not in a 1:1 ratio. The opposite is also true. If we double an orifice size, the effective area increase is quite a bit more than double-- it's FOUR TIMES the first amount. A 4" exhaust has 33% more diameter than a 3"-- but it has (7.06"^2 vs 12.56"^2) 44% more area.
What we have then is a ratio. There is a certain velocity associated with a certain back pressure in this ratio. We optimize this ratio be comparing the velocity to back pressure of different pipe sizes. For example, if we found that going from a 3" exhaust to a 4" gave us 30% less backpressure, but dropped our velocity by 50%, then we could probably say that we have taken a step backwards. A 5" exhaust in this case would make things even worse.
But what if we had a BOMBed diesel engine? in this case, a switch from a 3" exhaust to a 4" exhaust might yield 40%-50% less backpressure, but only a 10% decrease in velocity. In this case, the 4" exhaust would DEFINITELY be an upgrade that's worthwhile.
I believe the optimum exhaust diameter to be that point where the ratio goes from favoring velocity to favoring backpressure. The diameter of the exhaust at this "crossover point" will vary from one engine to another depending on how much air the engine is capable of putting into the exhaust. A Stock CTD running 20PSI of boost has a lot less airflow than a BOMBED CTD that's running 45psi.
So we can see that backpressure in and of itself may be good or bad, depending on which side of the ratio you are on. For the PSD in the article above, the stock system was just a little too small, thus the increase in hp when the new exhaust was installed.
Also, the reason the 3.5 inch downpipe is maintained is not because the engine "needs" the "proper backpressure". It is because the engine needs to have the highest velocity for a given restriction, and a sudden transition to a 4" pipe straight out of the turbo will cause a sudden expansion that slows and cools the flow.
If the PSD is equipped with a 4" tubine outlet, the the 4" downpipe would be better.
One last thought on this novel-- The "optimum" exhaust for a given engine only exist for a certain condition of fueling, boost, and rpm. So that exhaust that seems to be "perfect" at peak rpm hp is costing you engine performance at every rpm above and beneath that.
Because of their nature as machines always in transition, engines are nothing but compromises of compromises.
WHEW!
Justin
11-11-2003, 03:13 PM
#37
Registered User
Join Date: Apr 2003
Location: Cummins Technical Center, IN
Posts: 6,564
Likes: 0
Received 6 Likes
on
5 Posts
Re:OK...Back Pressure Shoot out! One and for all!
I forgot to mention that the baffles in many mufflers are placed in a spiral pattern to avoid standing waves. If they were all parallel to the exhaust flow, there would be waves reflected back and forth within the exhaust which induces certain unwanted resonances in pulsed exhaust flow.
The turbo on our trucks acts as an effective pulse damper, thus, the issue of standing/reflecting waves is of less concern on our trucks.
Justin
The turbo on our trucks acts as an effective pulse damper, thus, the issue of standing/reflecting waves is of less concern on our trucks.
Justin
11-11-2003, 04:12 PM
#39
Re:OK...Back Pressure Shoot out! One and for all!
The only way you can produce a vacuum at the turbine outlet is if you wrap your lips around your tailpipe and suck on it. :P
Not true...... helmholtz theory disproves that. Marksmith and rip rook (nwbombers) have built systems on that resonance theory.
You can tune a turbo diesel to self scavenge gasses. Based on pressure/standing wave theory you can create duplicity in the exhaust stream to enhance certain rpm ranges.
Not true...... helmholtz theory disproves that. Marksmith and rip rook (nwbombers) have built systems on that resonance theory.
You can tune a turbo diesel to self scavenge gasses. Based on pressure/standing wave theory you can create duplicity in the exhaust stream to enhance certain rpm ranges.
11-11-2003, 04:55 PM
#40
Registered User
Re:OK...Back Pressure Shoot out! One and for all!
I love the story about placing the tail pipe in a low pressure area under the car! Maybe someone can make a buck selling venturis to go on the end of the tail-pipe!! I wonder how fast you'd have to go for it to make a difference.
I like to think about this in terms of impedance matching: whenever you change the resistance in a circuit, you get a reflection at that point. It seems to me that if you could properly impedance match your turbo to the atmosphere (eg: make a laminarly flowing bell right on the turbine outlet) that would be the best solution, short of developing a vaccuum at the turbo outlet in some magical way. Right now this implies to me that as long as you have a turbulence-free flow from turbine to tail-pipe, the bigger the pipe the better -- even if the flow speed goes down, the mass flow should remain constant, and that is what the turbo should care about?
By the way, the evaporative cooling of hot water inside the freezer does not effect the mass adjusted cooling rate of the liquid, as at some point, the liquid in the hot cup will be at the temperature of the liquid in the cold cup . . .
Also, tuning the exhaust so that there is a standing wave pattern at certain engine speed/load combinations (the flow through these engines being dependent on rpms AND manifold pressure) isn't quite the same as creating a vacuum . . .
Interesting thread.
I like to think about this in terms of impedance matching: whenever you change the resistance in a circuit, you get a reflection at that point. It seems to me that if you could properly impedance match your turbo to the atmosphere (eg: make a laminarly flowing bell right on the turbine outlet) that would be the best solution, short of developing a vaccuum at the turbo outlet in some magical way. Right now this implies to me that as long as you have a turbulence-free flow from turbine to tail-pipe, the bigger the pipe the better -- even if the flow speed goes down, the mass flow should remain constant, and that is what the turbo should care about?
By the way, the evaporative cooling of hot water inside the freezer does not effect the mass adjusted cooling rate of the liquid, as at some point, the liquid in the hot cup will be at the temperature of the liquid in the cold cup . . .
Also, tuning the exhaust so that there is a standing wave pattern at certain engine speed/load combinations (the flow through these engines being dependent on rpms AND manifold pressure) isn't quite the same as creating a vacuum . . .
Interesting thread.
11-11-2003, 05:00 PM
#41
Registered User
Join Date: Dec 2002
Posts: 165
Likes: 0
Received 0 Likes
on
0 Posts
Re:OK...Back Pressure Shoot out! One and for all!
lol...you mean this one
D = Square Root of (CID × VE × RPM) ÷ ( V × 1130)
Where:
D = Pipe Diameter
CID = Cubic Inch Displacement
VE = Volumetric Efficiency
V = Velocity in ft/sec
I crunched some numbers for Rip one evening with regards to this.... :P
D = Square Root of (CID × VE × RPM) ÷ ( V × 1130)
Where:
D = Pipe Diameter
CID = Cubic Inch Displacement
VE = Volumetric Efficiency
V = Velocity in ft/sec
I crunched some numbers for Rip one evening with regards to this.... :P
11-11-2003, 05:04 PM
#42
Registered User
Join Date: Dec 2002
Posts: 165
Likes: 0
Received 0 Likes
on
0 Posts
Re:OK...Back Pressure Shoot out! One and for all!
[quote author=asilitch link=board=7;threadid=22079;start=30#msg208593 date=1068591347]
Also, tuning the exhaust so that there is a standing wave pattern at certain engine speed/load combinations (the flow through these engines being dependent on rpms AND manifold pressure) isn't quite the same as creating a vacuum . . .
Interesting thread.
[/quote]
BINGO, you could only tune this for a few specific RPM's and load conditions.....this is beast done to eliminate the dreaded exhaust drone that we all complain about
Also, tuning the exhaust so that there is a standing wave pattern at certain engine speed/load combinations (the flow through these engines being dependent on rpms AND manifold pressure) isn't quite the same as creating a vacuum . . .
Interesting thread.
[/quote]
BINGO, you could only tune this for a few specific RPM's and load conditions.....this is beast done to eliminate the dreaded exhaust drone that we all complain about
11-11-2003, 05:07 PM
#43
Re:OK...Back Pressure Shoot out! One and for all!
Also, tuning the exhaust so that there is a standing wave pattern at certain engine speed/load combinations (the flow through these engines being dependent on rpms AND manifold pressure) isn't quite the same as creating a vacuum . . .
Interesting thread.
Not quite a vacuum, but an 'enhancement' to the velocity of the spent gasses.
Not an original idea, helmholtz res has been used on intake manifolds in cars for years, most people just do not ralize it. the charecteristics involve a supercharging effect at the tuned frequency. GM's TPI is such a case, as was Fords dualstage manifols on the taurus SHO, the cross ram 413 wedge etc etc.
Similar principals can be applied to exhaust, just in the reverse
Interesting thread.
Not quite a vacuum, but an 'enhancement' to the velocity of the spent gasses.
Not an original idea, helmholtz res has been used on intake manifolds in cars for years, most people just do not ralize it. the charecteristics involve a supercharging effect at the tuned frequency. GM's TPI is such a case, as was Fords dualstage manifols on the taurus SHO, the cross ram 413 wedge etc etc.
Similar principals can be applied to exhaust, just in the reverse
11-11-2003, 05:11 PM
#45
Re:OK...Back Pressure Shoot out! One and for all!
[quote author=Diesel Freak link=board=7;threadid=22079;start=30#msg208594 date=1068591627]
lol...you mean this one
D = Square Root of (CID × VE × RPM) ÷ ( V × 1130)
Where:
D = Pipe Diameter
CID = Cubic Inch Displacement
VE = Volumetric Efficiency
V = Velocity in ft/sec
I crunched some numbers for Rip one evening with regards to this.... :P
[/quote]
What about the sound frequency calculations?.... you have the speed and volume present....
http://www.acoustics.salford.ac.uk/r...c_cox_book.htm
http://www.webs1.uidaho.edu/fluidsla...sis/report.pdf
http://www.soundsoft.demon.co.uk/abstract.htm
http://www.netero.com/0387983198/Fin...ical_Sciences/
Good reading materials.
lol...you mean this one
D = Square Root of (CID × VE × RPM) ÷ ( V × 1130)
Where:
D = Pipe Diameter
CID = Cubic Inch Displacement
VE = Volumetric Efficiency
V = Velocity in ft/sec
I crunched some numbers for Rip one evening with regards to this.... :P
[/quote]
What about the sound frequency calculations?.... you have the speed and volume present....
http://www.acoustics.salford.ac.uk/r...c_cox_book.htm
http://www.webs1.uidaho.edu/fluidsla...sis/report.pdf
http://www.soundsoft.demon.co.uk/abstract.htm
http://www.netero.com/0387983198/Fin...ical_Sciences/
Good reading materials.