Straight pipe on a JK
12-05-2007, 10:38 AM
#31
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The cats are retrictive but man, have you looked at these huge 3 foot mufflers these days. The ones on some rides are 3 ft around and seem like 5 ft long...lol.
Last edited by thumperk15; 12-05-2007 at 11:08 AM.
12-05-2007, 10:42 AM
#32
JK Junkie
Hmmmm. Did you say it "backfires"? Yah I can't see how that is good in California right now with all of the wild fires. Please do not drive that offroad near my house.
12-05-2007, 11:10 AM
#33
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HAHAHAHA...He may warp his valves if he cut his exhaust off behind his manifolds. That cold air will never make it back up to the heads from that far back...lol...accutally I have run open headers in alot of hotrods over the years and haven't warped my valves 1 time. Where are you getting your info at?and you too 1BADJK?
As far as the passager side goes if I put a pipe on last him I'd run it out the same side as it was stock...IMO.
and you too 1BADJK?As far as the passager side goes if I put a pipe on last him I'd run it out the same side as it was stock...IMO.
12-05-2007, 11:45 AM
#34
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For the record, I didn't write this, but it's true. I have spent years at the drag strip, and have built many a car without anything more than headers:
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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 computer-controlled engines don't have to worry about the effects described above, because the 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 computer'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.
----------------------------------------------------------------------------------------------------
Sorry for the "wall of text", but a precise, technical answer appeared to be warranted :-)
---------------------------------------------------------------------------------------------------
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 computer-controlled engines don't have to worry about the effects described above, because the 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 computer'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.
----------------------------------------------------------------------------------------------------
Sorry for the "wall of text", but a precise, technical answer appeared to be warranted :-)
12-05-2007, 11:55 AM
#35
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Thanks for the "wall of text" it was really helpful. I will most likely keep it this way, until a fixit ticket comes along. And one more comment to the user, who posted "why did he cut if off? when the clamps are right there"... lol and a sigh to myself
, If I knew a thing or two bout what I was doing or joined this forum sooner, I would've known. I don't why the mechanic didn't tell me either.
, If I knew a thing or two bout what I was doing or joined this forum sooner, I would've known. I don't why the mechanic didn't tell me either.
12-05-2007, 11:59 AM
#36
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Sarzilla
There's 2 opinions on that low end tourqe loss on the muffler. Don't put it back on just by anothers opinion. You wont warp a valve until maybe you go thru water like Slickwill and turn the key off when you hit the middle, flooding the hot engine in cold ass water then you may worry a little less about the valves and more about the water your hot engine took in.
There's 2 opinions on that low end tourqe loss on the muffler. Don't put it back on just by anothers opinion. You wont warp a valve until maybe you go thru water like Slickwill and turn the key off when you hit the middle, flooding the hot engine in cold ass water then you may worry a little less about the valves and more about the water your hot engine took in.
12-05-2007, 12:11 PM
#37
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And everyone knows that, well the ones that have seen your pics. This weekend I'm going to beat.....well not beat but get close to doing what you do in you JK . I like to KEEP the water out of mine
but wait until I get my carpet out and my Proline sprayed in.
I was using you as an example because your the only one I SEEN that goes thru rivers in yours...I think you need a boat or something, or do you forget what you bought...lol..not boat not even boat anywhere in the name Jeep Wrangler JK.
. I like to KEEP the water out of mine but wait until I get my carpet out and my Proline sprayed in.I was using you as an example because your the only one I SEEN that goes thru rivers in yours...I think you need a boat or something, or do you forget what you bought...lol..not boat not even boat anywhere in the name Jeep Wrangler JK.
Last edited by thumperk15; 12-05-2007 at 12:16 PM.
01-07-2015, 12:03 PM
#38
JK Newbie
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