Low End Torque
- Thread starter Tanzy
- Start date
i dunt have a cone air filter but a drop in one i have is the K&N one. what is de-meow?
i dont think i want to de-cat my system. any of u mateys out there lost any low end torque when u guys changed the rear muffler?
loveE3series
Well-Known Member
due to lost of back pressure?? dont de pussy yr ride if an auto
pls advise, im newbie
pls advise, im newbie
thats right. loss of back pressure.
yup mine is an auto.
yup mine is an auto.
well in that case i think it should not be all that significant. i can feel the difference but its very marginal. abit sluggish but after 3-4k revs, it is very responsive. much better than the stock.
loveE3series
Well-Known Member
humanfly said:
sorry mate, what im trying to get across is that we r not paying $$ to get worse response rite??? something is good for some cars but not all cars :screwedu: :screwedu: :laughlik: :laughlik:
only had my first 1.3 decat and change to remus, loss low end. the other i never touch exh :laughlik: :laughlik:
advise needed
Wayansurfer
Well-Known Member
Re: Low End Torque
Have you tried tuning it??whenever exhaust had been changed..the engine need retuning..just my 2 cents worth of experience
humanfly said:
Have you tried tuning it??whenever exhaust had been changed..the engine need retuning..just my 2 cents worth of experience
Crufty Dusty
Well-Known Member
humanfly said:
Why is "loss of back pressure" a commonly cited cause for "loss of low end torque"?
apparently i have been told to let it run it in first. maybe thats y i might be experiencing this. but maybe if it doesnt improve, then its time to OBIT!
Whisky_Tango
Core Group Members
Crufty Dusty said:
Pipe comes in many sizes (diameter). The cross-section of a pipe also the internal diameter which is also the area will determine the volume of liquid or gas inside the pipe for a given length.
General Idea:
For a fixed low flowrate, a smaller pipe diameter will produce higher pressure thus velocity also increases. But pressure & velocity drops with bigger diameter. Thus turbulence flow is created which is not desired and this could be the reason for lost of low end torque.
But what if now the flowrate increases tremendously?
Pressure will still continue to rise but now the velocity drops or maintains at a certain value. Bottleneck effect.
Solution here is to increase pipe diameter (assuming length the same) to release the pressure. Thus at high end, engine revs up faster.
Unless your exhaust system has a design (example spring loaded flap) to reduce the pipe diameter at low revs and at high revs it opens the flap for max flow. This will be ideal for not losing low end torque and also increase high end power.
In fluid dynamics, for a smooth flow with desired pressure and velocity is called laminar flow. This kind of flow is always desired and engineered in any pipe work.
Just imagine 10 ppl standing in a straight line with one arm's length away. A force (say a hard push) is applied on the last person. Only the first 5 ppl will experience the force but reduces in effect.
The gap between them will create turbulence flow effect!
Now if all 10 ppl were to stand closely packed, chest touching back. Effect is greater and travels faster to reach the 10th person. This is laminar flow effect.
Just my 2 cents.
the low end power loss associated with going really free flow can be compromised if cam phasing was changed to suit the new inlet-to-exhaust port pressure differential. It is a lot of work though, and I'm not sure that the current generation ECUs use VANOS or DVANOS to shift phasing to actively search for best torque. From BMW modders experiences it would appear it either does not, or span of control is small relative to the change.
WT bro, your 2 cents makes perfect cents (pun intended hahah.. corny!). I think 'turblence flow' should be 'turbulent flow' though.
Pipe transition angles of 7 degrees or less even at very high velocities still maintain laminar flow. Steps are bad.. gradual changes under 7 degrees are good.
WT bro, your 2 cents makes perfect cents (pun intended hahah.. corny!). I think 'turblence flow' should be 'turbulent flow' though.
Pipe transition angles of 7 degrees or less even at very high velocities still maintain laminar flow. Steps are bad.. gradual changes under 7 degrees are good.
Whisky_Tango
Core Group Members
Hehehe... Ryan why dont have spell check function ah...Shaun said:
Thanx... glad you can understand.SlowMo® said:Very well explained bro. Your 2 cents always worth a lot here
Its not easy to write something technical and hoping everyone can understand.
My in-depth research has led me to finding this article..i hope this helps some of u as well..
Cheers.
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.
- Adapted from Thomas V.
Cheers.
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.
- Adapted from Thomas V.
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