friend 93 civic ex sohc vtec has stright pipin....
11-21-2002, 09:10 PM
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friend 93 civic ex sohc vtec has stright pipin....
Some say that "an engine needs backpressure to work correctly." Is this true?
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 or their muffler removed. It is true that such valve burning does occur as a result of the exhaust modsor removing your muffler, 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. Which is accomplished by running "Open Headers" or removing your muffler .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. . Once vehicles receive performance mods that reduce backpressure, without properly "building up" for this they had that double-loading effect, and then tend 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 and you will lose torque as a result or a period of time. Please do not think it will take 6 months, a year or longer to start damaging your valves and seal's and to notice a loss in torque thus a loss in horsepower from doing the modifications without the proper knowledge of what you are doing. My advice to everyone out there running "straight pipes" or "open headers" that have not built thier engine to except these modifications, please do not do this to your cars, they come from the factoy this way for a reason, this is not to say not to do it if you have the money to put into your engine to replace seals and so forth to be able to do these modifications without burning valves, cause let's face it if you have the money to do it right the first time you are gonna save so much money in the long run. And that is what we all want right, we all want it done right the first time.
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 or their muffler removed. It is true that such valve burning does occur as a result of the exhaust modsor removing your muffler, 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. Which is accomplished by running "Open Headers" or removing your muffler .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. . Once vehicles receive performance mods that reduce backpressure, without properly "building up" for this they had that double-loading effect, and then tend 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 and you will lose torque as a result or a period of time. Please do not think it will take 6 months, a year or longer to start damaging your valves and seal's and to notice a loss in torque thus a loss in horsepower from doing the modifications without the proper knowledge of what you are doing. My advice to everyone out there running "straight pipes" or "open headers" that have not built thier engine to except these modifications, please do not do this to your cars, they come from the factoy this way for a reason, this is not to say not to do it if you have the money to put into your engine to replace seals and so forth to be able to do these modifications without burning valves, cause let's face it if you have the money to do it right the first time you are gonna save so much money in the long run. And that is what we all want right, we all want it done right the first time.
11-21-2002, 09:32 PM
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:booty: Come one guys you are always so quick to argue this whenever someone posts something like this....but it seems to me with over 1200 :jawdrop: people looking at it and no one has replied that you guys are leaving this subject alone...... fact or myth? This is backed up facts.... there is too much argument on this subject , whole lotta valve burnin going on with those who have no muffler or a "straight pipes." Guys people argue this on a daily basis but everyone starts to go with what another guy said and then another goes with the other two guys and before you know it you got 100 people agreeing on one point that one person wasn't sure it was true to begin with. Well I know sooner or later this is gonna get argued to death so I will let it go at that but an intresting artice none the less and there is truth to support it.
91accordcoupe :wavey:
91accordcoupe :wavey:
h:
11-21-2002, 09:45 PM
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yea but its all true thats why i posted it i posted one earlier and everyone was talking crap so i went out and got the article
:thumbup:
:thumbup:
11-21-2002, 10:15 PM
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open header adn straight pipe are VERY differant in terms of exhaust dynamics.. and you need to further view things on an individual basis.. you can not LUMP this stuff together... i know someone with a boen stock internaled turbo GSR who drovr it for months with turbo manifold to cat and thats ALL.. that thing is moving WAY more air than your friends stock EX... more than enough to break things if possible.. but hes not.. cars fine... my point is people will ALWAYS disgree on this for one simple reason.. there is NO ONE SIMPLE ANSWER.. really just theory
11-22-2002, 03:28 AM
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hes running a turbo???? dont turbos have stronger valves so it can handle the boost??????????? i would think that this article would make people think because it is true , why would someone type all that if it wasnt...
11-22-2002, 05:38 AM
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Originally posted by Nvious_Creation
hes running a turbo???? dont turbos have stronger valves so it can handle the boost??????????? i would think that this article would make people think because it is true , why would someone type all that if it wasnt...
hes running a turbo???? dont turbos have stronger valves so it can handle the boost??????????? i would think that this article would make people think because it is true , why would someone type all that if it wasnt...
re read my post.. "he is runnign a turbo on a BONE STOCK INTERNAL gsr.. " so no its STOCK engine internals
OMG... why would people send 8 million chain letters about bill gates giving them a million dollars if you foward it... because people are silly and do silly things.. MAYBE some of the article is true.. MAYBE NOT... the point is i have MULTIPLE examples of people running straight pipe or EVEN open header WITH NO adverse effects.. in fact in drag racing open headers is a COMMON practice among the domestic crowd..
11-22-2002, 01:23 PM
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well you guys can believe whatever you want i was just trying to help some people out..isnt that what these forums are for???? yet all you guys do is argue?wtf???
11-22-2002, 01:41 PM
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Originally posted by Nvious_Creation
well you guys can believe whatever you want i was just trying to help some people out..isnt that what these forums are for???? yet all you guys do is argue?wtf???
well you guys can believe whatever you want i was just trying to help some people out..isnt that what these forums are for???? yet all you guys do is argue?wtf???