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Old 01-30-2010, 10:16 AM
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Straight Pipe

So, today after work I am going down the my local muffler shop and having them drop the muffler and run a straight pipe with the stock resonator. I was quoted $125.00. I am getting the mount plates welded on either side, so if I don't like it I can easily put the muffler back in myself. I am not going for a few hours, I will have pics as well as a video posted by the end of the day. Its snowy up here in MA, and once I get them up I don't want to hear any bull about how dirty my Jeep is right now. I am not all that happy about it, waiting til Tuesday for $5 washes, I go once a week. I hate the salt and sand all over the place.

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  #2  
Old 01-30-2010, 10:22 AM
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Re: Straight Pipe

That is going to be loud as ****.

Might lose some performance with the loss of backpressure too. Let us know how it goes!
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Old 01-30-2010, 12:41 PM
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Re: Straight Pipe

That is going to some sweet music Ben
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Old 01-30-2010, 01:26 PM
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Re: Straight Pipe

cant wati to hear it bro! Dont worry about the backpressure thing...you got plenty of fresh, cool air coming in the front with your CAI.
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Old 01-30-2010, 01:27 PM
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Re: Straight Pipe

this sounds pretty decent imo....just something to think about

stock muffler with reso delete and cai

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Old 01-30-2010, 01:48 PM
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Re: Straight Pipe

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 vehicles don't have to worry about the effects described above, because the PCM ( 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 PCM'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.
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Old 01-30-2010, 05:30 PM
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Re: Straight Pipe

Soooo......This was an ok idea? This video is hilarious, it is 6 degrees outside and ice is everywhere, and I'm no Scorsese. The camera got blown away, glad it didnt break. It sounds pretty good, but I havent gotten a good pull yet cause its sooooooo icccyyy. Cant wait to get it cleaned up and situated. I will do in cabins too for all you sound haters! Music is meant to be heard a loud.

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Old 01-30-2010, 05:42 PM
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Re: Straight Pipe

Quote:
Originally Posted by Scottina06 View Post
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 vehicles don't have to worry about the effects described above, because the PCM ( 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 PCM'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.
Good read. I'm now edumacated on the subject.
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Old 01-30-2010, 05:48 PM
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Re: Straight Pipe

Quote:
Originally Posted by BenReardon View Post
Soooo......This was an ok idea? This video is hilarious, it is 6 degrees outside and ice is everywhere, and I'm no Scorsese. The camera got blown away, glad it didnt break. It sounds pretty good, but I havent gotten a good pull yet cause its sooooooo icccyyy. Cant wait to get it cleaned up and situated. I will do in cabins too for all you sound haters! Music is meant to be heard a loud.

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  #10  
Old 01-30-2010, 05:51 PM
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Re: Straight Pipe

I agree it sounds good! I thought it was gonna be WAY louder. Guess the resonator really does its job lol.
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Old 01-30-2010, 06:07 PM
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Re: Straight Pipe

I love it.
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Old 01-31-2010, 09:07 AM
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Re: Straight Pipe

That sounds AWESOME!!!!!!!
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