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Old 12-16-2011, 07:17 PM   #1
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3.8 Dual Exhaust

I have a 99 V6 with a CAI, 65mm Throttle Body and dual borala exhaust.

I'm putting MAC long tube headers and O/R H-pipe (2 1/2 inch) on. I was told that once i convert to true duals I will loose a significant amount of back pressure.

My current exhaust collects into a Y pipe then the stock headers.

What can I do if I don't want to loose back pressure??? Is there any way around that or should I just not worry about it since I have the throttle and CAI, then long tubes and h pipe.
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Old 12-16-2011, 08:51 PM   #2
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Re: 3.8 Dual Exhaust

Back pressure is for losers, lol

Just get your exhaust done and call it a day. Btw what mufflers are you gonna go with? I guessing MAC mufflers
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Old 12-16-2011, 09:15 PM   #3
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Quote:
Originally Posted by ssaleen1981
I have a 99 V6 with a CAI, 65mm Throttle Body and dual borala exhaust.

I'm putting MAC long tube headers and O/R H-pipe (2 1/2 inch) on. I was told that once i convert to true duals I will loose a significant amount of back pressure.

My current exhaust collects into a Y pipe then the stock headers.

What can I do if I don't want to loose back pressure??? Is there any way around that or should I just not worry about it since I have the throttle and CAI, then long tubes and h pipe.
0 back pressure on your car is a great thing!!... The engines in our cars are 4 Stroke motors!.. They require no back pressure!.. If there is some one saying to you, that you need a certain amount of back pressure for your car to run right!.. Then that individual knows nothing and is an idiot talking out their a**!!!!...... So open up that exhaust and let that pony breath!!!!! Lol
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Old 12-16-2011, 09:30 PM   #4
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Quote:
Originally Posted by Eturner

0 back pressure on your car is a great thing!!... The engines in our cars are 4 Stroke motors!.. They require no back pressure!.. If there is some one saying to you, that you need a certain amount of back pressure for your car to run right!.. Then that individual knows nothing and is an idiot talking out their a**!!!!...... So open up that exhaust and let that pony breath!!!!! Lol
I'm no idiot, unless your tuned for low back pressure you will lose bottom end power. Even if you have straight pipes w/ no mufflers you will have BP. Go unbolt your cat back/mufflers/tailpipes roughly half your current BP and come back and tell me how it runs.. You won't even be able to spin the tires.. Don't argue, go try it.
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Old 12-17-2011, 07:56 AM   #5
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Quote:
Originally Posted by deadsp0t

I'm no idiot, unless your tuned for low back pressure you will lose bottom end power. Even if you have straight pipes w/ no mufflers you will have BP. Go unbolt your cat back/mufflers/tailpipes roughly half your current BP and come back and tell me how it runs.. You won't even be able to spin the tires.. Don't argue, go try it.
Then you are the first one to have a 2 stroke motor in a Mustang!!!... As 2 stroke motors are the only ones that require any back pressure!!... If you are requiring a tune to regain bottom end power due to the "lack of back pressure" then you have a separate problem with your car!... Back pressure robs 4 stroke motors of power!!... End of story!....
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Old 12-17-2011, 08:25 AM   #6
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Quote:
Originally Posted by deadsp0t

I'm no idiot, unless your tuned for low back pressure you will lose bottom end power. Even if you have straight pipes w/ no mufflers you will have BP. Go unbolt your cat back/mufflers/tailpipes roughly half your current BP and come back and tell me how it runs.. You won't even be able to spin the tires.. Don't argue, go try it.
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Old 12-17-2011, 08:36 AM   #7
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Quote:
Originally Posted by Eturner

Then you are the first one to have a 2 stroke motor in a Mustang!!!... As 2 stroke motors are the only ones that require any back pressure!!... If you are requiring a tune to regain bottom end power due to the "lack of back pressure" then you have a separate problem with your car!... Back pressure robs 4 stroke motors of power!!... End of story!....
Lol. Like I said before arguing go do what I said and see for your self because you have no idea what your talking about at all and you are misleading ppl. Speak on what actual exp you have not what you've read. I would not take exhaust advise from someone who does not know how to determine the rear gear ratio, which is far less complicated.
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Old 12-17-2011, 08:38 AM   #8
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Eturner... Technically you're correct... But also extremely wrong. You would end up with more peak power, but your torque would be gone... And that's even with the car tuned for it.
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Old 12-17-2011, 08:41 AM   #9
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Quote:
Originally Posted by Las0mbra
Eturner... Technically you're correct... But also extremely wrong. You would end up with more peak power, but your torque would be gone... And that's even with the car tuned for it.
Dude you can't tell that guy anything, he knows and has done it all and refuses to believe anyone other then him could know anything about anything. Either that or he's trolling...
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Old 12-17-2011, 09:11 AM   #10
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Then if I'm so wrong then some one explain why my 60 ft times improve, and this is without a tune???...... 60ft times (at the drags) are representative of your low end power ( both torque and hp)!...

---------- Post added at 10:08 AM ---------- Previous post was at 10:05 AM ----------

Also anyone can please explain to me that if a certain amount of back pressure is needed!... Then why do you see race cars at all levels with out cats. and are basically straight piped??....

---------- Post added at 10:11 AM ---------- Previous post was at 10:08 AM ----------

Quote:
Originally Posted by deadsp0t

Dude you can't tell that guy anything, he knows and has done it all and refuses to believe anyone other then him could know anything about anything. Either that or he's trolling...
Oh ya there is a difference between trolling and having simple little debate!..
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Old 12-17-2011, 09:13 AM   #11
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Re: 3.8 Dual Exhaust

Thanks for the help -- I'm keeping the borla mufflers on the car for now. I don't know what type of borla they are, had flowmasters that sounded great, but rusted off, the borla exhaust gave me more pickup, with a quieter sound.

I will be getting a tune as well. After I change the spark plugs, install screaming demon coil, and add an upgraded 150 amp alternator.

Hope everything is worth it. I have been driving this car everyday for 10 years. has 182000 miles

I will post pics sometime in january when it is finished.
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Old 12-17-2011, 09:34 AM   #12
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Quote:
Originally Posted by Eturner
Then if I'm so wrong then some one explain why my 60 ft times improve, and this is without a tune???...... 60ft times (at the drags) are representative of your low end power ( both torque and hp)!...

---------- Post added at 10:08 AM ---------- Previous post was at 10:05 AM ----------

Also anyone can please explain to me that if a certain amount of back pressure is needed!... Then why do you see race cars at all levels with out cats. and are basically straight piped??....

---------- Post added at 10:11 AM ---------- Previous post was at 10:08 AM ----------



Oh ya there is a difference between trolling and having simple little debate!..
So you are running open headers and got improved 60ft times? Likely you removed the cats and improved 60ft? Like I said removed cats is REDUCED back pressure not ZERO. Are you seriously comparing a 3.8L V6 to a race motor? Hell are you seriously comparing your or my motor to a race motor, that's tuned? Even straight pipes with no mufflers provide a small amount of back pressure because of the diameter of the piping.

It's not a debate, the facts are the idea of reduced back pressure is a very good one, and the idea of zero back pressure on a street car is just wrong. Like I said before, go outside and unbolt your cat back. Leave it on the hangers, the tips will rest on the rear bumper and the front of the cat back won't drag no worries. Then drive it and tell me what you think about it. Your speaking based on something you read somewhere and speaking on something I've done before. If you are not willing to go outside and get some hands on exp then.. Well.. Go get some exp then we will talk if your not willing then you should not be talking about it like you have exp when you do not.
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Old 12-17-2011, 09:37 AM   #13
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Quote:
Originally Posted by ssaleen1981
Thanks for the help -- I'm keeping the borla mufflers on the car for now. I don't know what type of borla they are, had flowmasters that sounded great, but rusted off, the borla exhaust gave me more pickup, with a quieter sound.

I will be getting a tune as well. After I change the spark plugs, install screaming demon coil, and add an upgraded 150 amp alternator.

Hope everything is worth it. I have been driving this car everyday for 10 years. has 182000 miles

I will post pics sometime in january when it is finished.
Good! It will be worth it once you get all that done!! Sorry to jack your thread as an educational tool!

Be sure to post and let us know how it turns out for you!!!
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Old 12-17-2011, 09:59 AM   #14
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Re: 3.8 Dual Exhaust

Quote:
Originally Posted by deadsp0t View Post
Good! It will be worth it once you get all that done!! Sorry to jack your thread as an educational tool!

Be sure to post and let us know how it turns out for you!!!

I will, And I'm not too worried about the back pressure - I just dont want to drive up a hill and have the engine just rev. I'm sure that wont happen but....

This is not a racing application either -- I'm going for a better sound and to make the car fun to drive. Also hoping to gain some hp out of it too with the CAI, Throttle, Upgraded Spark Plugs, Wires, Coil, Tune, long tubes, h-pipe and mufflers -- i'm sure it will work out
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Old 12-17-2011, 10:01 AM   #15
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Quote:
Originally Posted by ssaleen1981

I will, And I'm not too worried about the back pressure - I just dont want to drive up a hill and have the engine just rev. I'm sure that wont happen but....

This is not a racing application either -- I'm going for a better sound and to make the car fun to drive. Also hoping to gain some hp out of it too with the CAI, Throttle, Upgraded Spark Plugs, Wires, Coil, Tune, long tubes, h-pipe and mufflers -- i'm sure it will work out
Sounds like you have a good plan! Stick to it don't flip flop or you'll end up with a bad combo! Can't wait to see the final results!
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Old 12-17-2011, 10:12 AM   #16
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Quote:
Originally Posted by deadsp0t

So you are running open headers and got improved 60ft times? Likely you removed the cats and improved 60ft? Like I said removed cats is REDUCED back pressure not ZERO. Are you seriously comparing a 3.8L V6 to a race motor? Hell are you seriously comparing your or my motor to a race motor, that's tuned? Even straight pipes with no mufflers provide a small amount of back pressure because of the diameter of the piping.

It's not a debate, the facts are the idea of reduced back pressure is a very good one, and the idea of zero back pressure on a street car is just wrong. Like I said before, go outside and unbolt your cat back. Leave it on the hangers, the tips will rest on the rear bumper and the front of the cat back won't drag no worries. Then drive it and tell me what you think about it. Your speaking based on something you read somewhere and speaking on something I've done before. If you are not willing to go outside and get some hands on exp then.. Well.. Go get some exp then we will talk if your not willing then you should not be talking about it like you have exp when you do not.
Really curious how back pressure on a street car is good??.... Back pressure makes it harder for the exhaust to exit!.. Causing the engine to work more!.. More work for the engine is a loss in total performance!.. So please enlighten me as to how back pressure on a street car is a good thing!..

And by the way!.. I had a 96 Monte-Carlo Z34 that I had removed the cats and all!.. Still had factory exhausts manifold on it!... And my all my times from 60ft through finale improved at the strip!... And no that car did not a tune in it!..
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Old 12-17-2011, 02:37 PM   #17
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It's fact that u need some back pressure.... Y do u think an x pipe helps it equals out the back pressure so the cylinders won't be "banking"
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Old 12-17-2011, 02:53 PM   #18
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Originally Posted by Fordhartbreaker
It's fact that u need some back pressure.... Y do u think an x pipe helps it equals out the back pressure so the cylinders won't be "banking"
They equal out the pressure between both banks!... So you dont get a lean condition and so on, on one side or the other!.. Back pressure is what is being forced back into the engine!... You have a 4 stroke motor!... Back pressure is not needed!...
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Old 12-17-2011, 03:08 PM   #19
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Quote:
Originally Posted by Eturner

They equal out the pressure between both banks!... So you dont get a lean condition and so on, on one side or the other!.. Back pressure is what is being forced back into the engine!... You have a 4 stroke motor!... Back pressure is not needed!...
Lmmfao... You keep saying that and ppl keep telling your wrong, because you are. Ppl are not just pulling your leg, we are trying to help you. Also I've never ever herd of a lean condition caused by too much back pressure! That's laughable!!!!!

Are you getting your info from that site thy gave you the info about your gears? Lmao
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Old 12-17-2011, 03:21 PM   #20
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Quote:
Originally Posted by deadsp0t

Lmmfao... You keep saying that and ppl keep telling your wrong, because you are. Ppl are not just pulling your leg, we are trying to help you. Also I've never ever herd of a lean condition caused by too much back pressure! That's laughable!!!!!

Are you getting your info from that site thy gave you the info about your gears? Lmao
Like I said before then!... Explain why you need back pressure!... You have given no proof or explanation to support your claims!..

---------- Post added at 04:21 PM ---------- Previous post was at 04:16 PM ----------

And as far as my gears are concerned!.. I actually looked at multiple sites!.. Not just one!... You should go back and reread that thread!..
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Old 12-17-2011, 03:49 PM   #21
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Quote:
Originally Posted by Eturner

Like I said before then!... Explain why you need back pressure!... You have given no proof or explanation to support your claims!..

---------- Post added at 04:21 PM ---------- Previous post was at 04:16 PM ----------

And as far as my gears are concerned!.. I actually looked at multiple sites!.. Not just one!... You should go back and reread that thread!..
I've offered you proof every time I've posted in regard to this.

Go unbolt your cat back! I say this because I've done this! I have driven the car thisway! I have my own exp! I've also started the car with just headers! Here's another example, why when you buy exhaust do they stop the pipe diameter at 2.5"? If zero BP was optimal why not 3"? Or 4"? I'm not talking stock I'm talking aftermarket upgrade. Stock is 2.25" upgrade is 2.5". I'm talking from my own personal exp. I've done the exhaust swaps on two of the three mustangs I've owned.

I can't give you a technical explanation cause I'm not an engineer, what I can offer is hands on real world exp. if you are not willing to get some exp for yourself on a MUSTANG then I can't help you if you are not willing to help yourself or learn.

With all this that's been said I'm done on this topic.
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Old 12-17-2011, 05:16 PM   #22
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Quote:
Originally Posted by deadsp0t

I've offered you proof every time I've posted in regard to this.

Go unbolt your cat back! I say this because I've done this! I have driven the car thisway! I have my own exp! I've also started the car with just headers! Here's another example, why when you buy exhaust do they stop the pipe diameter at 2.5"? If zero BP was optimal why not 3"? Or 4"? I'm not talking stock I'm talking aftermarket upgrade. Stock is 2.25" upgrade is 2.5". I'm talking from my own personal exp. I've done the exhaust swaps on two of the three mustangs I've owned.

I can't give you a technical explanation cause I'm not an engineer, what I can offer is hands on real world exp. if you are not willing to get some exp for yourself on a MUSTANG then I can't help you if you are not willing to help yourself or learn.

With all this that's been said I'm done on this topic.
Um..... As far as the diameter of the exhaust pipe!... The larger the diameter, such as 3 and 4 inch pipe!... Your exhaust gasses will cool much quicker!... You don't want that!... Typically 2.5 inch pipe is the best for street applications do to.... 1. It will not cool off as quickly as 3 or larger pipe will!... A street driven cars exhaust will not generally reach the same temps as say a race motor will!... 2. It offers better flow than 2.25 and smaller pipes will!...
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Old 12-17-2011, 11:11 PM   #23
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Re: 3.8 Dual Exhaust

Go find a farm tractor with an inline 4 or 6 cylinder...
Remove the exhaust manifold so that the exhaust gasses exit directly from the head.
Start it, and try to pull something... anything... hell, it will struggle trying to pull its own weight.

This is the result of ZERO back pressure.

Reinstall the exhaust system and you may resume pulling stumps or plows or whatever.
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Old 12-17-2011, 11:52 PM   #24
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For every one saying to "try running open headers", or "remove the exhaust manifold off a tractor and..." you are talking about some thing entirely different than Back Pressure!!... Educate your selves on how 2 stroke motors and how they work and why they need a certain amount of Back Pressure!!...
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Old 12-18-2011, 12:11 AM   #25
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I'm done with this thread u need to learn to be more open minded and not so stubborn were only trying to help man
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Old 12-18-2011, 12:24 AM   #26
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Here is another good read off of thumepertalk.com motor cycle forum that has some more insight.

Backpressure: The myth and why it's wrong.

I. Introduction
One of the most misunderstood concepts in exhaust theory is backpressure. People love to talk about backpressure on message boards with no real understanding of what it is and what it's consequences are. I'm sure many of you have heard or read the phrase "Engines need backpressure" when discussing exhaust upgrades. That phrase is in fact completely inaccurate and a wholly misguided notion.

II. Some basic exhaust theory
Your exhaust system is designed to evacuate gases from the combustion chamber quickly and efficently. Exhaust gases are not produced in a smooth stream; exhaust gases originate in pulses. A 4 cylinder motor will have 4 distinct pulses per complete engine cycle, a 6 cylinder has 6 pules and so on. The more pulses that are produced, the more continuous the exhaust flow. Backpressure can be loosely defined as the resistance to positive flow - in this case, the resistance to positive flow of the exhaust stream.

III. Backpressure and velocity
Some people operate under the misguided notion that wider pipes are more effective at clearing the combustion chamber than narrower pipes. It's not hard to see how this misconception is appealing - wider pipes have the capability to flow more than narrower pipes. So if they have the ability to flow more, why isn't "wider is better" a good rule of thumb for exhaust upgrading? In a word - VELOCITY. I'm sure that all of you have at one time used a garden hose w/o a spray nozzle on it. If you let the water just run unrestricted out of the house it flows at a rather slow rate. However, if you take your finger and cover part of the opening, the water will flow out at a much much faster rate.

The astute exhaust designer knows that you must balance flow capacity with velocity. You want the exhaust gases to exit the chamber and speed along at the highest velocity possible - you want a FAST exhaust stream. If you have two exhaust pulses of equal volume, one in a 2" pipe and one in a 3" pipe, the pulse in the 2" pipe will be traveling considerably FASTER than the pulse in the 3" pipe. While it is true that the narrower the pipe, the higher the velocity of the exiting gases, you want make sure the pipe is wide enough so that there is as little backpressure as possible while maintaining suitable exhaust gas velocity. Backpressure in it's most extreme form can lead to reversion of the exhaust stream - that is to say the exhaust flows backwards, which is not good. The trick is to have a pipe that that is as narrow as possible while having as close to zero backpressure as possible at the RPM range you want your power band to be located at. Exhaust pipe diameters are best suited to a particular RPM range. A smaller pipe diameter will produce higher exhaust velocities at a lower RPM but create unacceptably high amounts of backpressure at high rpm. Thus if your powerband is located 2-3000 RPM you'd want a narrower pipe than if your powerband is located at 8-9000RPM.

Many engineers try to work around the RPM specific nature of pipe diameters by using setups that are capable of creating a similar effect as a change in pipe diameter on the fly. The most advanced is Ferrari's which consists of two exhaust paths after the header - at low RPM only one path is open to maintain exhaust velocity, but as RPM climbs and exhaust volume increases, the second path is opened to curb backpressure - since there is greater exhaust volume there is no loss in flow velocity. BMW and Nissan use a simpler and less effective method - there is a single exhaust path to the muffler; the muffler has two paths; one path is closed at low RPM but both are open at high RPM.

IV. So how did this myth come to be?
I often wonder how the myth "Engines need backpressure" came to be. Mostly I believe it is a misunderstanding of what is going on with the exhaust stream as pipe diameters change. For instance, someone with a civic decides he's going to uprade his exhaust with a 3" diameter piping. Once it's installed the owner notices that he seems to have lost a good bit of power throughout the powerband. He makes the connections in the following manner: "My wider exhaust eliminated all backpressure but I lost power, therefore the motor must need some backpressure in order to make power." What he did not realize is that he killed off all his flow velocity by using such a ridiculously wide pipe. It would have been possible for him to achieve close to zero backpressure with a much narrower pipe - in that way he would not have lost all his flow velocity.

V. So why is exhaust velocity so important?
The faster an exhaust pulse moves, the better it can scavenge out all of the spent gasses during valve overlap. The guiding principles of exhaust pulse scavenging are a bit beyond the scope of this doc but the general idea is a fast moving pulse creates a low pressure area behind it. This low pressure area acts as a vacuum and draws along the air behind it. A similar example would be a vehicle traveling at a high rate of speed on a dusty road. There is a low pressure area immediately behind the moving vehicle - dust particles get sucked into this low pressure area causing it to collect on the back of the vehicle. This effect is most noticeable on vans and hatchbacks which tend to create large trailing low pressure areas - giving rise to the numerous "wash me please" messages written in the thickly collected dust on the rear door.

---------- Post added at 01:21 AM ---------- Previous post was at 01:20 AM ----------

Another good read on back pressure:

Destroying a myth.

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.

---------- Post added at 01:24 AM ---------- Previous post was at 01:21 AM ----------

This is just some of the reading I've done on this topic!... Some meaning a very small portion!...
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Old 12-18-2011, 01:26 AM   #27
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It's fact that u need some back pressure.... Y do u think an x pipe helps it equals out the back pressure so the cylinders won't be "banking"
Backpressure no, the x pipe helps increase scavenging which is hindered by backpressure.

---------- Post added at 01:26 AM ---------- Previous post was at 01:22 AM ----------

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They equal out the pressure between both banks!... So you dont get a lean condition and so on, on one side or the other!.. Back pressure is what is being forced back into the engine!... You have a 4 stroke motor!... Back pressure is not needed!...
Right about backpressure not being needed except on newer cars they are programmed for some backpressure. To fix it you would need to retune the car.
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Old 12-18-2011, 07:43 AM   #28
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Backpressure no, the x pipe helps increase scavenging which is hindered by backpressure.

---------- Post added at 01:26 AM ---------- Previous post was at 01:22 AM ----------



Right about backpressure not being needed except on newer cars they are programmed for some backpressure. To fix it you would need to retune the car.
Actually if you read my entire last post you will see that back pressure is not needed at all!.. Not on the newer or older cars!.. The retune just keeps the car from running to lean!.. Your car can lean out if your exhaust is flowing too well!!.... Lol.
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