Did I Lose Power?
01-12-2005, 06:04 PM
#21
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Join Date: Jul 2003
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RE: Did I Lose Power?
ORIGINAL: ohsoquik02
no it's been dyno proven, it will shift your torque and hp curves higher in the powerband
ORIGINAL: Dan02GT
2000GT4.6 summed it up, he knows his stuff!
But, I hate this myth so much I'm going to rant about it. Anyone who says you will lose torque and hp is a complete moron. It's the people who use the BUTT-DYNO to judge what they got for gains. Having a wide open exhaust increases torque and HP all across your powerband, but heres the kicker, the better your exhaust flows, the more it raises your HP & tq peak & the significant difference mid-range and upper-range power, fools the unknowledgable into believing they lost power off the line.
2000GT4.6 summed it up, he knows his stuff!
But, I hate this myth so much I'm going to rant about it. Anyone who says you will lose torque and hp is a complete moron. It's the people who use the BUTT-DYNO to judge what they got for gains. Having a wide open exhaust increases torque and HP all across your powerband, but heres the kicker, the better your exhaust flows, the more it raises your HP & tq peak & the significant difference mid-range and upper-range power, fools the unknowledgable into believing they lost power off the line.
01-12-2005, 10:07 PM
#22
2nd Gear Member
Join Date: Apr 2004
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Posts: 492
RE: Did I Lose Power?
i could see if you had a 4 or 6 cylinder car with stock manifolds and just straight pipes all the way out the back..but i dont quite see it with v8s..i mean...if that was true then people would keep there stock exhaust and how can headers give you 10-22ft pds of tourqe if you loose it?...yeah its crap of a myth
01-13-2005, 12:12 AM
#23
2nd Gear Member
Thread Starter
Join Date: Nov 2004
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Posts: 435
RE: Did I Lose Power?
Thanks for all your help, now i believe that if i get other mods i will benifit from my exhaust such as CAI to gain back any low tq/hp i may have loss and gain even more on high end, but i think a s/c sound better then a CAI 
01-13-2005, 01:08 AM
#25
3rd Gear Member
Join Date: May 2004
Location: California, Los angeles
Posts: 700
RE: Did I Lose Power?
ORIGINAL: OUZBnd
The truth about exhaust backpressure and torque.
"Some say that "an engine needs backpressure to work correctly." Is this true?
No. It would be more correct to say, "a perfectly stock engine that cannot adjust its fuel delivery needs backpressure to work correctly." This idea is a myth. As with all myths, however, there is a hint of fact with this one. Particularly, some people equate backpressure with torque, and others fear that too little backpressure will lead to valve burning.
The first reason why people say "backpressure is good" is because they believe that increased backpressure by itself will increase torque, particularly with a stock exhaust manifold. Granted, some stock manifolds act somewhat like performance headers at low RPM, but these manifolds will exhibit poor performance at higher RPM. This, however does not automatically lead to the conclusion that backpressure produces more torque. The increase in torque is not due to backpressure, but to the effects of changes in fuel/air mixture, which will be described in more detail below.
The other reason why people say "backpressure is good" is because they hear that cars (or motorcycles) that have had performance exhaust work done to them would then go on to burn exhaust valves. Now, it is true that such valve burning has occurred as a result of the exhaust mods, but it isn't due merely to a lack of backpressure.
The internal combustion engine is a complex, dynamic collection of different systems working together to convert the stored power in gasoline into mechanical energy to push a car down the road. Anytime one of these systems are modified, that mod will also indirectly affect the other systems, as well.
Now, valve burning occurs as a result of a very lean-burning engine. In order to achieve a theoretical optimal combustion, an engine needs 14.7 parts of oxygen by mass to 1 part of gasoline (again, by mass). This is referred to as a stochiometric (chemically correct) mixture, and is commonly referred to as a 14.7:1 mix. If an engine burns with less oxygen present (13:1, 12:1, etc...), it is said to run rich. Conversely, if the engine runs with more oxygen present (16:1, 17:1, etc...), it is said to run lean. Today's engines are designed to run at 14.7:1 for normally cruising, with rich mixtures on acceleration or warm-up, and lean mixtures while decelerating.
Getting back to the discussion, the reason that exhaust valves burn is because the engine is burning lean. Normal engines will tolerate lean burning for a little bit, but not for sustained periods of time. The reason why the engine is burning lean to begin with is that the reduction in backpressure is causing more air to be drawn into the combustion chamber than before. Earlier cars (and motorcycles) with carburetion often could not adjust because of the way that backpressure caused air to flow backwards through the carburetor after the air already got loaded down with fuel, and caused the air to receive a second load of fuel. While a bad design, it was nonetheless used in a lot of vehicles. Once these vehicles received performance mods that reduced backpressure, they no longer had that double-loading effect, and then tended to burn valves because of the resulting over-lean condition. This, incidentally, also provides a basis for the "torque increase" seen if backpressure is maintained. As the fuel/air mixture becomes leaner, the resultant combustion will produce progressively less and less of the force needed to produce torque.
Modern BMWs don't have to worry about the effects described above, because the DME (car's computer) that controls the engine will detect that the engine is burning leaner than before, and will adjust fuel injection to compensate. So, in effect, reducing backpressure really does two good things: The engine can use work otherwise spent pushing exhaust gas out the tailpipe to propel the car forward, and the engine breathes better. Of course, the DME's ability to adjust fuel injection is limited by the physical parameters of the injection system (such as injector maximum flow rate and fuel system pressure), but with exhaust backpressure reduction, these limits won't be reached."
The truth about exhaust backpressure and torque.
"Some say that "an engine needs backpressure to work correctly." Is this true?
No. It would be more correct to say, "a perfectly stock engine that cannot adjust its fuel delivery needs backpressure to work correctly." This idea is a myth. As with all myths, however, there is a hint of fact with this one. Particularly, some people equate backpressure with torque, and others fear that too little backpressure will lead to valve burning.
The first reason why people say "backpressure is good" is because they believe that increased backpressure by itself will increase torque, particularly with a stock exhaust manifold. Granted, some stock manifolds act somewhat like performance headers at low RPM, but these manifolds will exhibit poor performance at higher RPM. This, however does not automatically lead to the conclusion that backpressure produces more torque. The increase in torque is not due to backpressure, but to the effects of changes in fuel/air mixture, which will be described in more detail below.
The other reason why people say "backpressure is good" is because they hear that cars (or motorcycles) that have had performance exhaust work done to them would then go on to burn exhaust valves. Now, it is true that such valve burning has occurred as a result of the exhaust mods, but it isn't due merely to a lack of backpressure.
The internal combustion engine is a complex, dynamic collection of different systems working together to convert the stored power in gasoline into mechanical energy to push a car down the road. Anytime one of these systems are modified, that mod will also indirectly affect the other systems, as well.
Now, valve burning occurs as a result of a very lean-burning engine. In order to achieve a theoretical optimal combustion, an engine needs 14.7 parts of oxygen by mass to 1 part of gasoline (again, by mass). This is referred to as a stochiometric (chemically correct) mixture, and is commonly referred to as a 14.7:1 mix. If an engine burns with less oxygen present (13:1, 12:1, etc...), it is said to run rich. Conversely, if the engine runs with more oxygen present (16:1, 17:1, etc...), it is said to run lean. Today's engines are designed to run at 14.7:1 for normally cruising, with rich mixtures on acceleration or warm-up, and lean mixtures while decelerating.
Getting back to the discussion, the reason that exhaust valves burn is because the engine is burning lean. Normal engines will tolerate lean burning for a little bit, but not for sustained periods of time. The reason why the engine is burning lean to begin with is that the reduction in backpressure is causing more air to be drawn into the combustion chamber than before. Earlier cars (and motorcycles) with carburetion often could not adjust because of the way that backpressure caused air to flow backwards through the carburetor after the air already got loaded down with fuel, and caused the air to receive a second load of fuel. While a bad design, it was nonetheless used in a lot of vehicles. Once these vehicles received performance mods that reduced backpressure, they no longer had that double-loading effect, and then tended to burn valves because of the resulting over-lean condition. This, incidentally, also provides a basis for the "torque increase" seen if backpressure is maintained. As the fuel/air mixture becomes leaner, the resultant combustion will produce progressively less and less of the force needed to produce torque.
Modern BMWs don't have to worry about the effects described above, because the DME (car's computer) that controls the engine will detect that the engine is burning leaner than before, and will adjust fuel injection to compensate. So, in effect, reducing backpressure really does two good things: The engine can use work otherwise spent pushing exhaust gas out the tailpipe to propel the car forward, and the engine breathes better. Of course, the DME's ability to adjust fuel injection is limited by the physical parameters of the injection system (such as injector maximum flow rate and fuel system pressure), but with exhaust backpressure reduction, these limits won't be reached."
supreme post. i leanrd a **** load just now..im so happy cause i was wondering why my car reacted so much better on a warm up....thx againOUZbnd
01-13-2005, 07:37 AM
#26
3rd Gear Member
Join Date: May 2004
Location: California, Los angeles
Posts: 700
RE: Did I Lose Power?
okay wait a sec.... i read this :
"too large of a pipe diameter can hurt you.
A restrictive exhaust creates back pressure in the exhaust system that hurts your vehicle's performance in two ways:
1. The engine has to work harder to force exhaust gases out of the cylinders.
2. Engines cannot scavenge burned exhaust gases out of the cylinder efficiently. This leaves exhaust gases in the cylinder to dilute incoming air/fuel mixtures and rob your engine of horsepower.
Pipe Diameter:
A common misconception is that the larger the diameter, the better the system. But, bigger isn't always better. Systems that are too large in diameter can actually hurt low-end performance.
As a general rule, switching to a performance system that is 1/4" to 1/2" larger than stock will provide you with the best horsepower increases. To determine which pipe diameters will be best for your system, decide what RPM range your engine will operate at, most of the time. Smaller diameter pipers will produce low to mid RPM torque. Larger diameters produce mid to high RPM torque.
But keep in mind that if you increase the pipe diameter TOO large, then you have a much larger area the exiting exhaust must cover. If the engine pushes out "X" amount of exhaust, and the exhaust is too large and the exhaust exiting the engine cannot fill the pipe, it cools quickly, slows down, and causes a restriction also. The hotter you can keep the exhaust, the faster and easier it flows. This is one of the reasons why an off-road pipe loses some low-end but gains more top-end, which I hope you will understand with the example I use below.
If you want an example, take a straw and put a kink in it and blow thru it softly. Notice how some of the "exhaust" goes out but most stays in your mouth (engine). Now try blowing through it as hard as you can, simulating WOT and high rpms on a stock exhaust, notice how your are almost choking on your "exhaust" now, simulating poor flow at the benefit of more low-end torque.
Now, take a decent sized diameter straw (Mcdonald's straws work the best) and blow through it slowly. Notice how all air is going out the straw, and none is staying in your mouth (no backpressure, poor low-end torque). Now try again, but blow through it as hard as you can. Notice how all the air exits as fast as you can blow it, simulating a high flow exhaust, maybe TOO much.
The trick is to find the balance between the two. High-end flow, while saving low-end torque."
um....so u can def. loose power and its no myth or am i off topic here??
"too large of a pipe diameter can hurt you.
A restrictive exhaust creates back pressure in the exhaust system that hurts your vehicle's performance in two ways:
1. The engine has to work harder to force exhaust gases out of the cylinders.
2. Engines cannot scavenge burned exhaust gases out of the cylinder efficiently. This leaves exhaust gases in the cylinder to dilute incoming air/fuel mixtures and rob your engine of horsepower.
Pipe Diameter:
A common misconception is that the larger the diameter, the better the system. But, bigger isn't always better. Systems that are too large in diameter can actually hurt low-end performance.
As a general rule, switching to a performance system that is 1/4" to 1/2" larger than stock will provide you with the best horsepower increases. To determine which pipe diameters will be best for your system, decide what RPM range your engine will operate at, most of the time. Smaller diameter pipers will produce low to mid RPM torque. Larger diameters produce mid to high RPM torque.
But keep in mind that if you increase the pipe diameter TOO large, then you have a much larger area the exiting exhaust must cover. If the engine pushes out "X" amount of exhaust, and the exhaust is too large and the exhaust exiting the engine cannot fill the pipe, it cools quickly, slows down, and causes a restriction also. The hotter you can keep the exhaust, the faster and easier it flows. This is one of the reasons why an off-road pipe loses some low-end but gains more top-end, which I hope you will understand with the example I use below.
If you want an example, take a straw and put a kink in it and blow thru it softly. Notice how some of the "exhaust" goes out but most stays in your mouth (engine). Now try blowing through it as hard as you can, simulating WOT and high rpms on a stock exhaust, notice how your are almost choking on your "exhaust" now, simulating poor flow at the benefit of more low-end torque.
Now, take a decent sized diameter straw (Mcdonald's straws work the best) and blow through it slowly. Notice how all air is going out the straw, and none is staying in your mouth (no backpressure, poor low-end torque). Now try again, but blow through it as hard as you can. Notice how all the air exits as fast as you can blow it, simulating a high flow exhaust, maybe TOO much.
The trick is to find the balance between the two. High-end flow, while saving low-end torque."
um....so u can def. loose power and its no myth or am i off topic here??
01-13-2005, 03:40 PM
#27
Super Moderator
Join Date: Jan 2004
Location: IL
Posts: 10,637
RE: Did I Lose Power?
Put it this way...When Top Fuel dragsters make more power than any other engine in the world. What kind of exhaust do they use?? Thats right. None. Open headers.
So if having cats, mufflers, and tail pipes makes backpressure and it's good. Why don't they all use a full exhaust system? Backpressure is for 2 strokes.
So if having cats, mufflers, and tail pipes makes backpressure and it's good. Why don't they all use a full exhaust system? Backpressure is for 2 strokes.
01-13-2005, 04:00 PM
#28
6th Gear Member
Join Date: Nov 2003
Location: Pittsburgh, PA
Posts: 5,182
RE: Did I Lose Power?
ORIGINAL: sidewayz4.6
Put it this way...When Top Fuel dragsters make more power than any other engine in the world. What kind of exhaust do they use?? Thats right. None. Open headers.
So if having cats, mufflers, and tail pipes makes backpressure and it's good. Why don't they all use a full exhaust system? Backpressure is for 2 strokes.
Put it this way...When Top Fuel dragsters make more power than any other engine in the world. What kind of exhaust do they use?? Thats right. None. Open headers.
So if having cats, mufflers, and tail pipes makes backpressure and it's good. Why don't they all use a full exhaust system? Backpressure is for 2 strokes.
that's comparing apples/oranges besides those motors are rebuilt ever 3 or 4 runs
"the most powerful engines in the world" also use aluminum rods why dont' you put a set of those in your car
01-13-2005, 04:02 PM
#29
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Join Date: Jan 2004
Location: IL
Posts: 10,637
RE: Did I Lose Power?
We were talking about exhaust and gaining the most power. Now you're comparing apples and oranges.
They also run nitromethane and a giant *** supercharger. So?
And actually, they get torn down after every run.
They also run nitromethane and a giant *** supercharger. So?
And actually, they get torn down after every run.
01-13-2005, 04:32 PM
#30
6th Gear Member
Join Date: Nov 2003
Location: Pittsburgh, PA
Posts: 5,182
RE: Did I Lose Power?
ORIGINAL: sidewayz4.6
We were talking about exhaust and gaining the most power. Now you're comparing apples and oranges.
They also run nitromethane and a giant *** supercharger. So?
And actually, they get torn down after every run.
We were talking about exhaust and gaining the most power. Now you're comparing apples and oranges.
They also run nitromethane and a giant *** supercharger. So?
And actually, they get torn down after every run.