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Alright, so I have quite a few friends who run their cars open header. I can't tell you how many times I've asked them for the pros and cons of it (besides the increase in engine volume) only to get the response, "naw, there's no drawbacks." So what I'd like is to hear your opinions on it--preferably backed by some kind of legitimate source.
 

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back pressure is an important part of the balance man.
 

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I'van der Rohe
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exhaust in the interior, possibly carbon monoxide poisoning, impossibly loud driving experience, more vibration prone, zero emissions control.

It's only for drag track only cars. other than that it's pointless.
 

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exhaust in the interior, possibly carbon monoxide poisoning, impossibly loud driving experience, more vibration prone, zero emissions control.

It's only for drag track only cars. other than that it's pointless.
+1. I ran open headers on the Charger for a weekend of daily driving just to see what it was like and I would not drive the car over 2000 RPMs for fear that I would lose my hearing and car would vibrate itself apart, but it sounded like a cool idea at the time when I was in college. Also, the hot exhaust will cook anything in the surrounding undercarriage.
 

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Dont Catch
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Team-Integra.net said:

Myth 3: I Need A Little Bit of Backpressure For Midrange Power

THE MIGHTY BACKPRESSURE MYTH:

You want zero backpressure not some backpressure as you may sometimes hear from a salesman or an old timer V8 hot rodder.

Stock backpressure is around 16 psi in a GSR. Good aftermarket exhausts yield 2-5 psi backpressure. "Bolt-ons only" engine packages, in the past, used exhausts with some backpressure, since there is this incorrect belief that having a little backpressure prevents the fresh air/fuel from shooting into the header at cam overlap (when both the opening intake valve & the closing exhaust valve are simultaneously, partially open). The backpressure supposedly "pushed" the fresh air/fuel back into the combustion chamber rather than having it go into the header. This shooting of fresh air/fuel from the intake manifold and intake port into the header cannot happen at cam overlap, since the pressure inside the header is already much higher than on the intake side , even when there is zero backpressure.

In reality, having more backpressure reduces the difference between the higher pressure in the head's exhaust port and lower pressure in the header and cat. You need this difference in pressure going from the head to the exhaust system or "pressure gradient" to keep the exhaust flow speed or energy at a high level. Having some backpressure during cam overlap and the exhaust stroke means that the exhaust gas must now push against something and therefore, this backwards force slows exhaust gas down.

This need for backpressure no longer exists when you have a properly tuned (timed) engine and a good stepped header. In fact, increased backpressure may lead to backwards flow or "reversion", where the exhaust gas travels backwards into the combustion chamber and dilutes the fresh intake charge at cam overlap. At the very least, it slows exhaust flow velocity or energy and prevents the creation of a vacuum for scavenging.

So please ignore the obsolete "you should have at least some backpressure" sales pitch. It's all about the creating high exhaust flow velocity/speed or energy leaving the exhaust port, in order for the header-cat-exhaust SYSTEM to do it's job properly (i.e. remove all the burnt exhaust gases and help pull in fresh intake charge by scavenging at cam overlap) and make power for you.

Regarding the backpressure issue:

Many people use backpressure to get midrange driveability at the sacrifice of lower power potential at the upper powerband rpms. Using back pressure is the wrong way to build a high performance exhaust system. The exhaust system should extract the exhaust from the header, to minimize parasitic pumping pressures.

The proper way to make an exhaust system that will act as an extractor is to properly size the tubing so that the the exhaust gas' flow velocity creates a "vacuum" behind the header.

Also, you have to realize that making a sytem which provides the best performance at all throttle positions and all powerband rpm ranges is next to impossible. There's always going to be a compromise and giving up some optimal power potential in one area of the rpm range.

You must tune the exhaust size/length for the throttle positions and rpm ranges where you want the most performance knowing that you'll sacrifice performance at the other end of the rpm range.
anyhow... for the G2s anyway... running open header will be way too loud especially for a DD. i have a video of mine. :D

btw if you really want to do this i think the best way to go about it would be to get a e-cutout... QTP sells em
 

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Find Em Fuck Em Forget Em
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Wrong. :D

Backpressure is always bad, period.
+1

This backpressure myth won't die.

Backpressure negatively effects Volumetric Efficiency, as it is a restriction. Higher VE means better fuel economy, power, and torque.

Open headers can be a great idea, but just unbolting the y-pipe isn't the best way, IMO.

Ideally you make up some turnouts to route the exhaust gas away from the cabin of the car. I've used cone inserts before with success, to keep the noise more reasonable, similar to these: Dynatech Vortex Insert Cones - JEGS
 

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The proper way to make an exhaust system that will act as an extractor is to properly size the tubing so that the the exhaust gas' flow velocity creates a "vacuum" behind the header.
I vaguely remember hearing something about this a couple years back, now I understand, good info.
 

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Yes it was a Maxima.
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The proper way to make an exhaust system that will act as an extractor is to properly size the tubing so that the the exhaust gas' flow velocity creates a "vacuum" behind the header.
Yeah, this is similar to intake manifold tuning, where you want to give the runners (or stacks) a length that will resonate at a certain frequency of intake pulses which relates to a given engine speed (RPM).
 

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Just Another Guy
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:rofl: :rofl: :rofl:

Not this back pressure talk again. Exhaust flow velocity > back pressure. Restriction makes me shudder.

Reminds me of this video: YouTube - 350z Riced out 2

"What exhaust are you running"

"Stock exhaust"

"oh yeah...back pressure and all

:rofl: :rofl: :rofl:

-Ed
 

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KA8 Legend Killer
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:rofl: :rofl: :rofl:

Not this back pressure talk again. Exhaust flow velocity > back pressure. Restriction makes me shudder.

Reminds me of this video: YouTube - 350z Riced out 2

"What exhaust are you running"

"Stock exhaust"

"oh yeah...back pressure and all

:rofl: :rofl: :rofl:

-Ed
That was one of if not the ugliest 350Z i've ever seen
 

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Life Ruiner
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.....back pressure...

When I dyno, then redyno minutes later with the muffler removed and loose 3whp peak what does that mean? This was a consistent loss and gain.


Truth be told, many people including myself confuse back pressure with air flow velocity and scavenging, because its sounds like a proper way of describing what is or is not happening.

~Dv8
 

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Tristate Committee Member
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in the older cars it dont matter if you run open or full exhaust. newer cars are different. taking out the exhaust is actually slowing you down.

and christan just removing muffler doesnt really show how much power you lost. yea your going to loose 2-3. but take off your catback, and your loosing over 5.
 
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