Backpressure
07-07-2008, 11:33 AM
#28
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Its not backpressure that improves the low end. Pressure in the exhaust of any kind is bad.
Its proper exhaust sizing that allows maximum exhaust gas velocity at the lowest amount of pressure to aid in exhaust gas scavenging.
Too large of a pipe will not allow maximum exhaust velocity. Too small and it creates backpressure.
Its proper exhaust sizing that allows maximum exhaust gas velocity at the lowest amount of pressure to aid in exhaust gas scavenging.
Too large of a pipe will not allow maximum exhaust velocity. Too small and it creates backpressure.
07-07-2008, 11:51 AM
#29
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Its not backpressure that improves the low end. Pressure in the exhaust of any kind is bad.
Its proper exhaust sizing that allows maximum exhaust gas velocity at the lowest amount of pressure to aid in exhaust gas scavenging.
Too large of a pipe will not allow maximum exhaust velocity. Too small and it creates backpressure.
Its proper exhaust sizing that allows maximum exhaust gas velocity at the lowest amount of pressure to aid in exhaust gas scavenging.
Too large of a pipe will not allow maximum exhaust velocity. Too small and it creates backpressure.
07-07-2008, 12:45 PM
#30
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My goal was keep as much low end torque as possible as our cars are **** on top end.
Now we get to my current car. I want ZERO back pressure as much as possible. I have no use for it.
07-07-2008, 12:50 PM
#31
It's not so much as having back pressure as to having the RIGHT amount. Too much backpressure you are 'choking' the engine to little you lose low end torque. I did not want to lose low end torque so I stuck with 2 1/2" and a two muffler setup and I was fine.
My goal was keep as much low end torque as possible as our cars are **** on top end.
Now we get to my current car. I want ZERO back pressure as much as possible. I have no use for it.
My goal was keep as much low end torque as possible as our cars are **** on top end.
Now we get to my current car. I want ZERO back pressure as much as possible. I have no use for it.
07-07-2008, 12:52 PM
#32
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Pretty much had straight pipes on the Cobalt and low end sucked like *****. Added a new muffler and a resonator notice a little gain back only noticed in 2nd gear as I got a little bit of bite back. How much do not know. Did not have it dyno tested. Do not have all that money to dyno a car after each and every mod.
07-07-2008, 01:01 PM
#34
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Kind of hard to back myself up as:
No dyno results
Do not have car anymore
Exhaust was custom
So all I have is first person experience. But on my current car I can back up how turboed cars do not need back pressure...whenever I go to a full 3" exhaust.
No dyno results
Do not have car anymore
Exhaust was custom
So all I have is first person experience. But on my current car I can back up how turboed cars do not need back pressure...whenever I go to a full 3" exhaust.
07-07-2008, 01:11 PM
#35
Pretty much had straight pipes on the Cobalt and low end sucked like *****. Added a new muffler and a resonator notice a little gain back only noticed in 2nd gear as I got a little bit of bite back. How much do not know. Did not have it dyno tested. Do not have all that money to dyno a car after each and every mod.
the straight pipe was probably too big. 2 1/4 or possibly even 2" would be ideal for true straight pipes on a cobalt. i bet you had bigger than that, most people do 2 1/2 which is too big. using the incorrect size is most likely why you felt like the car lost power.
i assure you it had nothing to do with backpressure, and "seat of the pants" is not exactly scientific proof.
seat of the pants aside, tell me how backpressure can possibly help low end torque. don't say "well when i did xxxx it felt different" i mean really, explain how you think it can help.
most likely, it's just something you have heard since it's such a huge myth that gets passed along. i would suggest reading up a little on backpressure. if you knew what backpressure really is, i doubt you would still think that it is a good thing. not knocking, because it's a popular myth. but i would recommend doing a quick google search or something.
07-07-2008, 01:17 PM
#36
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the question was "how does backpressure increase low end torque".
the straight pipe was probably too big. 2 1/4 or possibly even 2" would be ideal for true straight pipes on a cobalt. i bet you had bigger than that, most people do 2 1/2 which is too big. using the incorrect size is most likely why you felt like the car lost power.
i assure you it had nothing to do with backpressure, and "seat of the pants" is not exactly scientific proof.
seat of the pants aside, tell me how backpressure can possibly help low end torque. don't say "well when i did xxxx it felt different" i mean really, explain how you think it can help.
most likely, it's just something you have heard since it's such a huge myth that gets passed along. i would suggest reading up a little on backpressure. if you knew what backpressure really is, i doubt you would still think that it is a good thing. not knocking, because it's a popular myth. but i would recommend doing a quick google search or something.
the straight pipe was probably too big. 2 1/4 or possibly even 2" would be ideal for true straight pipes on a cobalt. i bet you had bigger than that, most people do 2 1/2 which is too big. using the incorrect size is most likely why you felt like the car lost power.
i assure you it had nothing to do with backpressure, and "seat of the pants" is not exactly scientific proof.
seat of the pants aside, tell me how backpressure can possibly help low end torque. don't say "well when i did xxxx it felt different" i mean really, explain how you think it can help.
most likely, it's just something you have heard since it's such a huge myth that gets passed along. i would suggest reading up a little on backpressure. if you knew what backpressure really is, i doubt you would still think that it is a good thing. not knocking, because it's a popular myth. but i would recommend doing a quick google search or something.
Exhaust is tricky as hell. I here people talking about running 2 1/2 to 3 straight and bitch about losing power. I forgot that if you decrease the diameter of a pipe you can still run straight as the diameter allows for the correct amount of exhaust flow so I am agreeing with you there. My opinion was on 2 1/2 and up. So you got me good on the 2 1/4 and below. Until you mentioned the smaller diameter I was not thinking about it mind was stuck on 2.5^.
07-07-2008, 01:19 PM
#37
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I will say this, I went from a CA header/dp and a 2.5" exhaust to a Pacesetter header (3" outlet) to a catless 3" exhaust, and I did notice less low end torque. However, I definately made that up in the higher rpms. I hate to say it but my car screams after 4500, and with a 2.8" pulley, it doesnt take long to get to 4500 rpm.
07-07-2008, 01:20 PM
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I will say this, I went from a CA header/dp and a 2.5" exhaust to a Pacesetter header (3" outlet) to a catless 3" exhaust, and I did notice less low end torque. However, I definately made that up in the higher rpms. I hate to say it but my car screams after 4500, and with a 2.8" pulley, it doesnt take long to get to 4500 rpm.
You guys have awesome highend going with bigger exhaust helped you guys open up highend.
07-07-2008, 01:28 PM
#41
Originally Posted by blackout06s
I had 2 1/2 piping and a cheap ass muffler which was same diameter and well it was pretty much setup like a glasspack. Which I just added a little more restriction in the flow even though it was 2 1/2 It probably had the flow as what your talking about 2 - 2 1/4. On the 2 1/2 like you said it was too big and I needed a little backpressure to feel the gains of a 2- 2 1/4 straight pipe setup.
Exhaust is tricky as hell. I here people talking about running 2 1/2 to 3 straight and bitch about losing power. I forgot that if you decrease the diameter of a pipe you can still run straight as the diameter allows for the correct amount of exhaust flow so I am agreeing with you there. My opinion was on 2 1/2 and up. So you got me good on the 2 1/4 and below. Until you mentioned the smaller diameter I was not thinking about it mind was stuck on 2.5^.
Exhaust is tricky as hell. I here people talking about running 2 1/2 to 3 straight and bitch about losing power. I forgot that if you decrease the diameter of a pipe you can still run straight as the diameter allows for the correct amount of exhaust flow so I am agreeing with you there. My opinion was on 2 1/2 and up. So you got me good on the 2 1/4 and below. Until you mentioned the smaller diameter I was not thinking about it mind was stuck on 2.5^.
in simple terms, let me tell you what backpressure is. your engine blows out air. the air needs to get out of the exhaust. having the proper size exhaust give you the proper EXHAST VELOCITY. the idea is to get the air out the end of the exhaust as quickly as possible. if the exhaust is too big, the air kinda "dribbles out" the end. if the exhaust is too small, the engine has to work harder to "force" the air out. having just the right size piping however gets the air out fast enough, lets the engine run more efficiently, and doesn't create any drag.
now, backpressure and why it's bad. backpressure is jsut what it sounds like. air moving the WRONG way through the exhaust, back towards the engine. when you have backpressure, your engine now has to work harder, because the air it is trying to force out is being pushed back towards it.
i like to use a straw and spitball analogy, because it's easy to understand. take a spitball, (represents the air coming out of the engine) put it in a straw, (represents your exhaust) and blow. if the spitball is the right size for the straw, it shoots out across the room with very little effort. take that same spitball, and take a paper towel roll, (exhaust that's too big) and try to spit it across the room. doesn't work. it just flops out the end. doesn't seem like anything, but if you were spitting thousands of spitballs, they would be hitting each other holding up the flow.
so now, let's say you are trying to spit the spitball, and someone else goes on the other end of the straw and starts blowing back at you. that's backpressure. you're trying to shoot the spitball, and someone else is blowing it back at you.
that being said, in no way, shape, or form is backpressure good, regardless of engine, car, type of induction, etc.
i hope this makes more sense and helps you realize why backpressure is no good, and also why the size of the pipe is also very important.
07-07-2008, 01:37 PM
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getting there!~
in simple terms, let me tell you what backpressure is. your engine blows out air. the air needs to get out of the exhaust. having the proper size exhaust give you the proper EXHAST VELOCITY. the idea is to get the air out the end of the exhaust as quickly as possible. if the exhaust is too big, the air kinda "dribbles out" the end. if the exhaust is too small, the engine has to work harder to "force" the air out. having just the right size piping however gets the air out fast enough, lets the engine run more efficiently, and doesn't create any drag.
now, backpressure and why it's bad. backpressure is jsut what it sounds like. air moving the WRONG way through the exhaust, back towards the engine. when you have backpressure, your engine now has to work harder, because the air it is trying to force out is being pushed back towards it.
i like to use a straw and spitball analogy, because it's easy to understand. take a spitball, (represents the air coming out of the engine) put it in a straw, (represents your exhaust) and blow. if the spitball is the right size for the straw, it shoots out across the room with very little effort. take that same spitball, and take a paper towel roll, (exhaust that's too big) and try to spit it across the room. doesn't work. it just flops out the end. doesn't seem like anything, but if you were spitting thousands of spitballs, they would be hitting each other holding up the flow.
so now, let's say you are trying to spit the spitball, and someone else goes on the other end of the straw and starts blowing back at you. that's backpressure. you're trying to shoot the spitball, and someone else is blowing it back at you.
that being said, in no way, shape, or form is backpressure good, regardless of engine, car, type of induction, etc.
i hope this makes more sense and helps you realize why backpressure is no good, and also why the size of the pipe is also very important.
in simple terms, let me tell you what backpressure is. your engine blows out air. the air needs to get out of the exhaust. having the proper size exhaust give you the proper EXHAST VELOCITY. the idea is to get the air out the end of the exhaust as quickly as possible. if the exhaust is too big, the air kinda "dribbles out" the end. if the exhaust is too small, the engine has to work harder to "force" the air out. having just the right size piping however gets the air out fast enough, lets the engine run more efficiently, and doesn't create any drag.
now, backpressure and why it's bad. backpressure is jsut what it sounds like. air moving the WRONG way through the exhaust, back towards the engine. when you have backpressure, your engine now has to work harder, because the air it is trying to force out is being pushed back towards it.
i like to use a straw and spitball analogy, because it's easy to understand. take a spitball, (represents the air coming out of the engine) put it in a straw, (represents your exhaust) and blow. if the spitball is the right size for the straw, it shoots out across the room with very little effort. take that same spitball, and take a paper towel roll, (exhaust that's too big) and try to spit it across the room. doesn't work. it just flops out the end. doesn't seem like anything, but if you were spitting thousands of spitballs, they would be hitting each other holding up the flow.
so now, let's say you are trying to spit the spitball, and someone else goes on the other end of the straw and starts blowing back at you. that's backpressure. you're trying to shoot the spitball, and someone else is blowing it back at you.
that being said, in no way, shape, or form is backpressure good, regardless of engine, car, type of induction, etc.
i hope this makes more sense and helps you realize why backpressure is no good, and also why the size of the pipe is also very important.
Pretty much my exhaust was too big and to compensate for that I just added more restriction in the exhaust. So in alls it just got confused as backpressure when really it was just oversized pipe. Going back to suck on my auto bottle didn't get winged properly.
07-07-2008, 08:12 PM
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07-07-2008, 10:00 PM
#45
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On the other person. Does taking paper towerl roll and bitch slapping the person trying to blow back at you count.
Pretty much my exhaust was too big and to compensate for that I just added more restriction in the exhaust. So in alls it just got confused as backpressure when really it was just oversized pipe. Going back to suck on my auto bottle didn't get winged properly.
Pretty much my exhaust was too big and to compensate for that I just added more restriction in the exhaust. So in alls it just got confused as backpressure when really it was just oversized pipe. Going back to suck on my auto bottle didn't get winged properly.
07-07-2008, 10:04 PM
#46
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good analogies d4, though i would say backpressure isnt someone blowing back...
its more like someone putting their hand over the end of the tube with just a tiny hole left open....
the pressure built up by your own breath (exhaust gasses) creates the reverse pressure.
its more like someone putting their hand over the end of the tube with just a tiny hole left open....
the pressure built up by your own breath (exhaust gasses) creates the reverse pressure.
07-07-2008, 10:07 PM
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07-07-2008, 10:09 PM
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to use the spit ball analogy further it's like putting a spit ball in the straw that's too big for the straw and trying to blow it out.
I know I'm just messin with ya.
On a side not I just bought a Megan cat back and I'm stoked! Can't wait for it to come...
I know I'm just messin with ya.
On a side not I just bought a Megan cat back and I'm stoked! Can't wait for it to come...
Last edited by Tazmanian_Dvl; 07-07-2008 at 10:10 PM. Reason: Automerged Doublepost
07-08-2008, 07:55 AM
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nice analogy and completely true too big a straw "exhaust pipe" and the ball slowly falls out the other end. A nice snug fit and it launches right out :P
Last edited by Whitty; 07-08-2008 at 07:55 AM. Reason: forgot to end the quote tag