# single to dual tip exhaust



## nilreb (Mar 17, 2012)

would gas mileage suffer if i switch to dual tip? i have an oem dual tip from a 225 with 50k. 
i have a 180 2001 quattro. i was planning to switch but now i think a single tip looks cleaner.


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## Mantvis (Jan 1, 2010)

nilreb said:


> would gas mileage suffer if i switch to dual tip? i have an oem dual tip from a 225 with 50k.
> i have a 180 2001 quattro. i was planning to switch but now i think a single tip looks cleaner.


I went from single to dual, looks much nicer.
Gas mileage will not suffer. Why would it?


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## 1fast2liter (Apr 4, 2005)

if you had the whole catback system it would even perform better as stock 180 is 2inch.. and looks alot cleaner too


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## TTC2k5 (May 23, 2008)

nilreb said:


> ...i was planning to switch but now i think a single tip looks cleaner.


No, single tip is like a single-tiTTied woman. May be "cleaner," but just not right.


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## Marcus_Aurelius (Mar 1, 2012)

TTC2k5 said:


> No, single tip is like a single-tiTTied woman. May be "cleaner," but just not right.


Bob, IMO function > form in something that marginally alters the the car's lines. I went from double to single tip in my car and like it a lot better. A performance advantage that doesn't take away much from the aesthetics is a win.


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## TTC2k5 (May 23, 2008)

Marcus_Aurelius said:


> Bob, IMO function > form in something that marginally alters the the car's lines. I went from double to single tip in my car and like it a lot better. A performance advantage that doesn't take away much from the aesthetics is a win.



Still not right Max, still not right. ;-)


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## Chuckmeister87 (Nov 10, 2009)

Why did single tip perform better? What was the difference? I thought increased flow was increased power..


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## Marcus_Aurelius (Mar 1, 2012)

TTC2k5 said:


> Still not right Max, still not right. ;-)


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## Marcus_Aurelius (Mar 1, 2012)

Chuckmeister87 said:


> Why did single tip perform better? What was the difference? I thought increased flow was increased power..


Your statement is right, increased flow is increased power (up to a point as velocity needs to be taken into account as well). What you're not realizing is that any bends and *splits*, negatively impacts overall flow. Simply put, the most efficient setup would be the straightest one with the least amount of bends, splits and restrictions (chambered mufflers and catalytic converters).

The most efficient way to make this happen in a TT, is with straight-trough everything exiting on the driver's side. Obviously there will be a few bends involved, but nothing major to impact flow like it would've with the splits and significant bends necessary to accommodate a dual exit. :beer:

This is how it's done in my car:


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## TTC2k5 (May 23, 2008)

Marcus_Aurelius said:


> Your statement is right, increased flow is increased power (up to a point as velocity needs to be taken into account as well). What you're not realizing is that any bends and *splits*, negatively impacts overall flow. Simply put, the most efficient setup would be the straightest one with the least amount of bends, splits and restrictions (chambered mufflers and catalytic converters).
> 
> The most efficient way to make this happen in a TT, is with straight-trough everything exiting on the driver's side. Obviously there will be a few bends involved, but nothing major to impact flow like it would've with the splits and significant bends necessary to accommodate a dual exit. :beer:
> 
> ...


I'm not convinced a dual pipe set up with a few bend/splits is significantly less efficient. Certainly if you can reduce the effects of friction, flow would be increased...but let's see the math beginning with F = mA. :laugh: 



cheers


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## 1fast2liter (Apr 4, 2005)

ouch thats funny. and i even get it..lol


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## Arnolds64 (Nov 13, 2009)

*I have thought about going to a single.*



Marcus_Aurelius said:


> Your statement is right, increased flow is increased power (up to a point as velocity needs to be taken into account as well). What you're not realizing is that any bends and *splits*, negatively impacts overall flow. Simply put, the most efficient setup would be the straightest one with the least amount of bends, splits and restrictions (chambered mufflers and catalytic converters).
> 
> The most efficient way to make this happen in a TT, is with straight-trough everything exiting on the driver's side. Obviously there will be a few bends involved, but nothing major to impact flow like it would've with the splits and significant bends necessary to accommodate a dual exit. :beer:
> 
> This is how it's done in my car:


Exactly what I thought. Plus it is much cheaper to do with a standard muffler and a muff shop could do it much easier. Got a get a single valance though. If yours is read maybe we could swap?
Spend some money on a really nice single tip as well not two.


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## Arnolds64 (Nov 13, 2009)

*Performance?*

So MAXarcus do you feel you gained some power with the single over the dual (Stock?) Hey I am going to eventually get a stock Y pipe I had decatted put on. Going cheapo catless without buying the 3 Inch down pipe. Betcha I get a nice gain without the cost. So far 75.00. I am think it will cost me about 150.00 max to do.


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## Arnolds64 (Nov 13, 2009)

*MPG.*

Less restriction is usually more power, mpg and noise. I can tell you that taking off cats is huge power on most all cars. Don't let anyone tell you different. I love it how the readers or the people that have never done this will tell you that it won't. Just like doing Home head porting. I have done this many times and has always gained me serious HP. Also less restriction picks up 2 mpg on most and I notice this especially my old Mustang GT's. I live in KC Mo and they do not sniff thank God. You are supposed to have what looks like a Cat only. However if you have friends you don't have to do that either. 

For you Greeny's. Look up East Anglia University - Climate Gate. It is all a lie to get a Carbon tax worldwide. It is only about money. SCAM.


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## darrenbyrnes (Jan 4, 2005)

Arnolds64 said:


> It is all a lie to get a Carbon tax worldwide. It is only about money. SCAM.



Do you get more power when you tighten your tinfoil hat??

http://www.scientificamerican.com/article.cfm?id=negating-climategate

/It's not a scam, but a couple TT's without their CATs won't do much to accelerate it. 

:beer::beer::beer:


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## babarber (Nov 3, 2008)

i would think the obvious weight reduction of less piping and 1 less muffler should be added to the list of benefits


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## Marcus_Aurelius (Mar 1, 2012)

TTC2k5 said:


> I'm not convinced a dual pipe set up with a few bend/splits is significantly less efficient. Certainly if you can reduce the effects of friction, flow would be increased...but let's see the math beginning with F = mA. :laugh:
> cheers


Well Bob, to be convinced you would have to start by looking at it the right way (F=mA is not what would be applicable here). 

The key element is *Pressure*. Remember that the engine is nothing more than a giant air pump, and anything impeding the ingestion and evacuation of said air is a power robber. The proper way to describe and discuss what is happening in the exhaust track is to look at pressure variances across components, bends, and splits. Much like the charge piping, any pressure change increases the effort needed to evacuate gases left over from combustion. We all can agree that energy is only made in one of the 4 strokes, therefore increasing the pressure needed to get the exhaust gases out, takes away energy that could be used to move the crankshaft (making more power). This can be easily monitored by placing a pressure gauge before and after a bend or a split to record the change in pressure. The extra amount of pressure variance from making a dual tip would determine the loss in power. How much is it? That's up for debate, but I know that I was able to free up a good chunk of TQ by parting ways with the split tip shenanigan.

To tie this into our lowly single vs dual tip discussion, flow into the exhaust piping is very turbulent. The shortest length of piping would offer the least amount of overall restriction and turbulence (quantified by pressure changes). Adding a split and significant amount of length to the total length of piping is in itself a power compromise. On top of that, the extra bends compounds the drawbacks and makes it less appropriate for pure performance.

This is an extract of an article that went into details about the laws involved. It will do a much better job than I can at describing everything in effect in a turbocharged exhaust system.


*
"The exhaust system is designed to deliver hot, harmful fumes from the engine bay and vent it to the atmosphere more openly. It should perform this function as efficiently as possible, i.e. it should result in the lowest loss in horsepower possible. Indeed, one can think of the exhaust system as one large restrictor. In terms of performance, it serves no purpose except to route the hot air away from the engine to make sure it ingests cool air. A consequence of the existence of an exhaust system is a reduction in the sound of the engine. This is due to the restrictions in the exhaust system causing a reduction in flow from the exhaust ports of the engine to the end of the exhaust pipe. In the automotive industry, this flow reduction is referred to as back pressure. In the interest of reducing noise further, mufflers are installed on the exhaust. Much of their noise-reducing qualities come from the implementation of a variety of acoustic techniques to quiet the sound of the combustion of the engine. Further reduction in sound comes as a result of acoustic wave damping by the piping.

An aside on back pressure

Officially, back pressure is the resistance of a fluid to obstructions in wall-bounded flows. This resistance causes a reduction in flow in the exhaust system. To more easily illustrate this, imagine pumping air through a constant diameter pipe with various obstructions. If you were to measure the dynamic pressure at the beginning and end of the pipe, the difference in the two measurements would be the back pressure. Hence, the ultimate goal in performance exhaust design is to have as little back pressure as possible.

There is a great deal of confusion within the performance community regarding back pressure, and this is the result of the term pressure being thrown around without clarification. When someone refers to a drop in pressure in an exhaust system, they are referring to dynamic pressure. This drop in dynamic pressure is the result of a reduction in exhaust velocity due to obstructions and friction of the pipe. It is imperative that you understand that Bernoulli’s principle does not apply in flow through long pipes, and therefore the dynamic pressure drop results in a drop in total pressure as well! For more information on the effect of friction on pressure loss in a pipe, see the Darcy-Weisbach equation

Exhaust flow is always turbulent

In reading some articles by enthusiasts regarding exhaust flow, I stumbled upon a few of them referring to laminar flow in the pipe. This was quite troubling to me since the flow in the pipe will never be laminar! To prove this, I introduce the Reynolds number, a ratio of inertial forces to viscous forces defined as Re = (V * L) / nu , where V is the fluid velocity, L is the characteristic length (diameter of the pipe for pipe flow), and nu is the kinematic viscosity of the fluid.

The Reynolds number is a well-known value in aerodynamics and has a variety of uses. One of these uses is defining transition of a flow from laminar to turbulent in a variety of flow fields. This is done empirically and can therefore vary based on the characteristics of the flow field, such as surface roughness, flow uniformity, and for wall-bounded flows, the shape of the wall. For pipe flow, transition to turbulence occurs generally at Re > 2300 with fully developed turbulence occurring at Re > 4000. Let us take a look at what kind of Reynolds numbers we will see in our car.

If we take the density of the gas to be 1.2 kg/m^3 (a fair guess assuming stoic air/fuel ratio), use a characteristic length of 0.075 meter (close to 3 inches) and take the dynamic viscosity to be 3 * 10^-5 kg/m-s (assuming 400 degrees Celcius), we get a Reynolds number of 27,000V. This means that for this flow to remain fully laminar, our exhaust velocity would have to be about 0.08 m/s. You can’t achieve that even at idle! Hence, your exhaust flow will be turbulent in all conditions (except when it’s off).

Why turbulence in exhaust is bad

You’ll often hear of products claiming to reduce turbulence in the exhaust resulting in a net gain in horsepower. But what is the turbulence doing that’s so bad? The main thing you need to know about turbulence is that it is inherently unstable and chaotic. One of the consequences of this trait is that skin friction for turbulent flows is much greater than in the laminar case. The result of this is in pipe flow is increased drag, which leads to greater back pressure. While bends and obstructions in the exhaust system yield lower exhaust velocity, they also result in higher turbulent intensity which exacerbates the losses.

Deeper analysis of bends in exhaust

We’ve already covered the fact that bends increase turbulence and decrease flow velocity. One thing that I have not seen covered by other enthusiasts is a physical explanation of what actually happens to the fluid going through a bend that causes these traits to occur.

Assume that we have a mandrel-bent pipe (a pipe with constant radius throughout the bend) with a relatively short bend so that viscous diffusion effects are negligible. As the gas approaches the bend, the fluid must be accelerated inward, so a streamwise total pressure gradient is established in the flow field. This is why bends increase back pressure and reduce exhaust velocity at the end of the pipe. Effects on turbulence come from the secondary flow resulting from the pressure gradient. Slower fluid is present on the inside of the pipe while faster fluid is kept outside. This introduces a rotation relative to the mean streamline of the flow, resulting in vorticity in the streamwise direction. This vorticity increases the instability of the flow.

1) An ideal exhaust system has as few bends as possible.
2) Turbulence will exist in your exhaust system at all engine conditions.
3) We should work to reduce turbulence in exhaust as much as possible. To remedy, see #1.
4) Heat should be conserved as much as possible in an exhaust system.
5) Back pressure is bad. To remedy, see #1 and #4.
6) Exhaust pipe diameter should be selected based on the size that yields the most area under the power curve.
7) Tuning exhaust runners is extremely complex and expensive and involves many variables, and is also dependent on turbocharger size.


*


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## Marcus_Aurelius (Mar 1, 2012)

Arnolds64 said:


> So MAXarcus do you feel you gained some power with the single over the dual (Stock?) Hey I am going to eventually get a stock Y pipe I had decatted put on. Going cheapo catless without buying the 3 Inch down pipe. Betcha I get a nice gain without the cost. So far 75.00. I am think it will cost me about 150.00 max to do.


With all else equal, you're always going to free up power by having a straighter single exit. The result is not exclusive to certain setups but all turbocharged TTs in general (from stock to heavily modified). :beer:


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## Chuckmeister87 (Nov 10, 2009)

I understand your concern about restriction on the flow, but I'm sure a split right after the cat wouldn't cause too much turbulence in the flow, and would increase flow if it was being restrained at all by the single exhaust port. The key factor is having enough power to make it more effective to go dual exhaust over single exhaust. I think anyone pushing more than 250hp should have dual exhaust.... Oh, and you haven't yet given any tangible evidence to go with your conclusion about single-port being better.


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## Marcus_Aurelius (Mar 1, 2012)

Chuckmeister87 said:


> I understand your concern about restriction on the flow, but I'm sure a split right after the cat wouldn't cause too much turbulence in the flow, and would increase flow if it was being restrained at all by the single exhaust port. The key factor is having enough power to make it more effective to go dual exhaust over single exhaust. I think anyone pushing more than 250hp should have dual exhaust.... Oh, and you haven't yet given any tangible evidence to go with your conclusion about single-port being better.


:banghead::banghead::banghead:

What would you describe as tangible evidence? I love it when people refuting facts ask for "evidence" or "proof" when they have nothing to back up their position on the subject. So far, I have been the only one making an attempt to give "evidence" to support my argument, I'm sorry if my posts didn't cut it for you yet. 

I could easily go out, spend a little bit of time, drill a few holes and test pressure variance before and after various restrictions in the exhaust. The data would be clear as day to show the impact. But why should I do it for something I already know, and would still be challenged by someone that doesn't even understand the concept? 

When you come up with timeless statements like "I think that anyone pushing more than 250hp should have dual exhaust" it's almost impossible to be taken seriously. I have years of experience making power out of turbo cars while bound by sanctioning rules, and I'm probably pushing the envelope more than anyone did or even thought possible on a factory KKK. Do you think for a second that I would go through the trouble of making the straightest possible exhaust, with the least amount of restrictions, just to give up power? I have a sponsored car that could get pretty much any exhaust I desire, yet I choose the one that's unfit for my power level.

Get back to me when you start pushing 250 HP the the wheels, get acquainted with a dyno, start doing your homework to come up with sound theories, and learn to test things properly. For now, I know you're not doing any of these so sit back and learn a thing or two :wave:


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## 20v master (May 7, 2009)

Chuckmeister87 said:


> I think anyone pushing more than 250hp should have dual exhaust.... Oh, and you haven't yet given any tangible evidence to go with your conclusion about single-port being better.


Seriously Max, :banghead::banghead::banghead:

It's just like IC piping. Reduction in number and length of bends decreases pressure drops. Straight = no bends. It has nothing to do with dual tip vs single or splits or not. My 500hp setup has no problems with a single exhaust tip. :screwy: Fluid dynamics is so interesting but such a PITA to prove anything. That's why you grasp the concepts and leave the calculations to the fluid dynamicists, aka less bends is better. The exhaust gas velocity along the inner edge of a bend must slow down to accomodate the longer distance the gas on the outer edge has to travel. This slowing and it's effects push to the middle of the exhaust gas stream and limit max velocity. It's a pretty simple concept. 

Now, as far as putting a 225 catback on a 180Q, the front cat flanges are different, so you can't use the cats from the 225 to mate to the 180Q DP. The midpipe of the 225 exhaust is 2.5" while the 180Q is 60mm, ~2.17". You can have an adapter made at an exhaust shop, or they can weld a piece of 2.5" pipe over the outlet of the 180Q cats, that will slip fit into the OEM clamp for the 225 midpipe. Also, the right rear edge of the 225 catback would hit the tow hook bracket on my 180Q over really rough roads or bumps. No one had mentioned this in any threads I read on swapping to the 225 catback, but I removed the tow hook and the banging noises/contact went away. I did notice ~2mpg better economy with the larger piping of the 225 catback. :thumbup:


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## Marcus_Aurelius (Mar 1, 2012)

^^ I am sure the internet wizards would still find some BS to challenge the engineer. However, I have to admit that they have one universal law going for them, "if one = good --> two = gooder"
:laugh: :laugh:


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## 20v master (May 7, 2009)

I keep getting Chickenman and Chuckmeister confused by simply glancing at their names. Sometimes, I'm like "Wow, this guy knows what he's talking about." Others, I'm all "WTF is this guy talking about." :laugh:


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## Marcus_Aurelius (Mar 1, 2012)

20v master said:


> I keep getting Chickenman and Chuckmeister confused by simply glancing at their names. Sometimes, I'm like "Wow, this guy knows what he's talking about." Others, I'm all "WTF is this guy talking about." :laugh:


Oh yeah, the similarities end with the phonetics of the screen names. They are actually polar opposites, residing at different ends of a certain spectrum.


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## 1fast2liter (Apr 4, 2005)

all comes down to velocity and restriction.. if you can make a system that keeps its over all velocity with little back pressure is ideal..... hence why alot of cars that are serious about performance run a good single exit exhaust... now this really only applys to 4 cylinders as v6s and 8's can benifit from a true duel set up with a quality tuned header that creates max scavaging in the cylinders.... (scavaging is the effect of one exhaust pulse creating a vacum in the header that helps clear the next cylinder in line and inducing a complete or as complete as possible intake charge. in laymans terms.) systems that use to large of primaries and exhaust tubing over all loses velicity and the gases cool and be sucked back in wich causes poor performace in low end and gas mileage... now in a turbo application thats not all to applicable. you wouldnt throw a 5inch system on our cars but all of us now that the lil dnky 60mm on a 180 is worthless. that being said exhaust will take the path of least resistance. inducing a dual tip set up will inturn induce turbulance wich can and has a negitive impact on flow... as always their are exceptions to the rule. motorcycles can benifit form a tuned exhaust system but make more peak hp and tq with a quality 2-1 setup( i am refering to harleys here) i had a sportster that was capped at 85whp and 84wtq went to a vance and hinse short shot system picked up mid range power.. went to a tuned stepped primary design and went to 101whp and 98wtq.)... mustangs run true duals from the factory with a h pipe or upgrades to a x pipe to even out exhaust flow do to the way the engine fires. but a well made true duel set up usually with stepped primaries always runs the best with the minimal amount of back pressure. a turbo car just runs better with a single exhuast. their is a point were a person isnt pushing enough to make a difference at that point to make the most or max out is were the upgrade takes place...... maybe if you didnt understand max's post you can understand mine....... at least it makes since to me...lol


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## ttwsm (Feb 27, 2011)

20v master said:


> I keep getting Chickenman and Chuckmeister confused by simply glancing at their names. Sometimes, I'm like "Wow, this guy knows what he's talking about." Others, I'm all "WTF is this guy talking about." :laugh:


x2 totally hear you on that one.


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## ttwsm (Feb 27, 2011)

Right or wrong, here's how I think of it. The exhaust always starts at the same pressure, based on charge into the cylinder and final temperature after combustion / cylinder movement up to exhaust valve opening. And it ends at the same pressure after it leaves the exhaust system (atmospheric). Broadening to energy, it's basically the same picture, save for velocity dissipation that may happen post-exhaust exit.

But anyway, the exhaust is going to give up a certain amount of energy on its way from the cylinder to the pipe exit. The question is where. You want it to give up as much energy as possible to the turbo. Anything you do to reduce other losses (fewer bends, larger pipe diameter, better exhaust manifold, etc.) will put more energy into the turbo, and of course into the unavoidable expansion losses upon exit from the tailpipe.


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## chrisc351 (Feb 17, 2011)

If I swapped out my 2" single tip exhaust on my 185 to a 3" OEM exhaust and deleted the res would it be noticeably louder?


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## 1fast2liter (Apr 4, 2005)

chrisc351 said:


> If I swapped out my 2" single tip exhaust on my 185 to a 3" OEM exhaust and deleted the res would it be noticeably louder?


Their is no 3inch oem exhaust it was 60mm and 2.5. No not louder still be the same. The audi stock mufflers are actually very quite. I had to cut mine open and modify it and i run a catless dp. If you go 42draft or apr or billy boat then yes be alot louder then stock. 

Sent from my Motorola Electrify using Tapatalk 2


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## nilreb (Mar 17, 2012)

alright. i guess stock dual tip with all the bends and turns won't make any difference, neither in HP or fuel consumption. 
now back to aesthetics.. i have the silver and honeycomb dual port valance. i'll have to try it out and see which one i like, since i can't decide on anything.


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## 20v master (May 7, 2009)

20v master said:


> I did notice ~2mpg better economy with the larger piping of the 225 catback. :thumbup:


Also slightly better spool. Slight, but still a difference.


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## coachvtt (Jan 16, 2008)

*dual to single*

I went from the dual 225tt to single exhaust 3" from DP out to 3" round Magnaflow muffler..
no res...Louder, hell yea!
One turbo one exhaust..just wanted to change it up..


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## Chuckmeister87 (Nov 10, 2009)

Max,
Tangible evidence would be numbers. A man fundamentally based on the scientific method, such as yourself, must have numbers somewhere to support his claim that his moving from dual exhaust to single port is better.




> Since there is one downpipe (and up pipe and mid pipe) there is no need for a dual exhaust and no negatives associated with a single exhaust. BUT:
> 
> Let's consider a dual 3" system vs a single 3"
> 
> ...



Stop saying single port is better without the numbers to prove it, please.opcorn:


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## PLAYED TT (Oct 17, 2010)

Marcus_Aurelius said:


> "if one = good --> two = gooder"
> :laugh: :laugh:


Quoting this because I literally lol'd. Why anyone is arguing this is beyond me. Quickest way out is what you want. For anyone who drives their car on the street only and measures performance gains by the butt feeling shouldnt worry about it. If you want 2 tips go for it. If you want one tip go for it. Chances are you wont notice a change nor will you care if you did....my $.02


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## Marcus_Aurelius (Mar 1, 2012)

Chuckmeister87 said:


> Max,
> Tangible evidence would be numbers. A man fundamentally based on the scientific method, such as yourself, must have numbers somewhere to support his claim that his moving from dual exhaust to single port is better.


Once again, someone bringing a refuting argument with nothing to show for it but demanding proof. :screwy: As I said, if I needed I could easily drill some holes and plumb high temperature pressure probes (which I have) before and after various splits and bends to show their effect to pressure, flow, and ultimately power. But, what incentive do I have to go out of my way, when I already know the outcome? Prove you wrong?




Chuckmeister87 said:


> Stop saying single port is better without the numbers to prove it, please.opcorn:


I'm not sure you fully understand what you're arguing. We have a single bank of cylinders, a single manifold, single turbo leading to a single hotside and downpipe. The ideal exhaust would be a short straight piece of piping with something like a v-stack at the tip to help the transition to open atmospheric conditions. Adding anything to that blueprint is a compromise to flow and power. In other words, any additional foot of piping, bend, split, merge, muffling or emission device is removing flow and power to the ideal conditions mentioned above. I'm sure even the most simplistic mind can agree that the dual tip design required to fit the TT bumper holes (spreaded far apart), requires a great deal of additional piping, a split, and at least two major 90* bends. What do you think that does to flow and power over the straightest shot to the back?


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## Chuckmeister87 (Nov 10, 2009)

Dyno your car. Single port dyno runs and dual port using the same exhaust. Show us the change. No drilling or anything elaborate that would put extra variables. Dyno.


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## TTC2k5 (May 23, 2008)

Marcus_Aurelius said:


> Once again, someone bringing a refuting argument with nothing to show for it but demanding proof. :screwy: As I said, if I needed I could easily drill some holes and plumb high temperature pressure probes (which I have) before and after various splits and bends to show their effect to pressure, flow, and ultimately power. But, what incentive do I have to go out of my way, when I already know the outcome? Prove you wrong?
> 
> 
> 
> ...


I think what most people have a hard time accepting is that a single 3in pipe (cross sectional area = 7.065 sq-in) with few bends/angles will exhaust more efficiently than a dual system, with significanlty greater capacity but slightly more bends/angles to slow down the exhaust.


edit: like this one for the 3.2 TT:











bob


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## Marcus_Aurelius (Mar 1, 2012)

Chuckmeister87 said:


> Dyno your car. Single port dyno runs and dual port using the same exhaust. Show us the change. No drilling or anything elaborate that would put extra variables. Dyno.


Still doesn't say what the incentives are for me! Plus, if you're so interested in having someone proving that the round wheel is the best design, why don't you set out to try the experiment yourself? I don't think your car would disintegrate if strapped to a dyno... Would it ???

I have nothing to gain, while you have nothing to loose from such an endeavor. I'm positive your exhaust could use some improvement and a trip to a dyno can be beneficial to your knowledge. Build a straight single tip catback section and dyno it before and after. If you win and there is no improvement, you still have baselined your power figures, proved the madman wrong and reinvited a better designed w heel. You could go down in history as the guy that defeated the laws of physics! Oh... Maybe you've already done so with your controversial intake that lost power with more flow. :wave:


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## Marcus_Aurelius (Mar 1, 2012)

TTC2k5 said:


> I think what most people have a hard time accepting is that a single 3in pipe (cross sectional area = 7.065 sq-in) with few bends/angles will exhaust more efficiently than a dual system, with significanlty greater capacity but slightly more bends/angles to slow down the exhaust.
> 
> 
> edit: like this one for the 3.2 TT:
> ...


Bob, I can't believe this is so difficult for people to grasp!

The dual tip system pictured has twice the muffling restrictions, extra unnecessary bends, a turbulent split, and finally more piping length. If the cross sectional is already appropriate for the application (which it is on 1.8l of displacement and small to mid size turbos), adding overall piping volume does nothing but decrease velocity (another unwanted byproduct). You do the math! :beer:


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## babarber (Nov 3, 2008)

the science of a single tip is simple and proven already max doesnt have to dyno it just because you cant wrap your head around any other number then HP

if it still doesnt prove anything to you then get a piece of 1/4 hose 6 inches long and blow through it
now take the same size hose and make it several feet long then coil it up like a garden hose and blow through one end you will see the same effect


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## Tempes_TT (Oct 24, 2010)

Max... shame on you. Im going to call you out on this. 

Because quote...

_"Never argue with stupid people, they will drag you down to their level and then beat you with experience."_

:laugh:


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## Marcus_Aurelius (Mar 1, 2012)

Tempes_TT said:


> Max... shame on you. Im going to call you out on this.
> 
> Because quote...
> 
> ...


Touché my friend, touché! 

Somehow I'm hanging to the hope that Chuck doesn't fall in that bracket despite his stubbornness!


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## TTC2k5 (May 23, 2008)

Another perspective:

http://www.performance928.com/cgi-bin/page_display.cgi?page_nav_name=singlevsduRm8&pass_parent=1125

and the text that goes with the above charts:

"1. Single pipe or dual pipe. A single pipe system will usually weigh less, cost less, and be simpler to install than a dual pipe exhaust system. The argument in favor of the dual system is that the dual pipe exhaust is easier to mount closer to the underside of the car and is less likely to hang down and look unsightly. The smaller diameter dual pipe mufflers are easier to conceal and usually do a better job than the larger single pipe muffler. I like the sound quality of dual pipes vs. single pipe systems, but that is a personal subjective opinion only. Dyno testing I've done show that both single pipes and dual pipes with equivalent flow capacities will make equal top end power. However, the dual pipe system makes more torque below 5500 rpm."


Note: this is not for our 1.8s but it does address 1 versus 2 pipes.




cheers


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## Chuckmeister87 (Nov 10, 2009)

TTC2k5 said:


> Another perspective:
> 
> http://www.performance928.com/cgi-bin/page_display.cgi?page_nav_name=singlevsduRm8&pass_parent=1125
> 
> ...


Thank you TTcK


Someone from the Porsche community actually recording the changes rather than sit back on "what should be, and here is the science to prove it". There very well be some variable you forgot to take into account, Max, or something you just completely did not expect in which you can then explain scientifically. You don't just use THEORY and say it's correct without the proper documentation. I do not question your vast knowledge you have obtained relating to horsepower and handling, but you simply need evidence.


As for the claim that two mufflers on two different exiting ports is bad, performance mufflers have been designed to even out the pulses that exhaust exits in. Many mufflers decrease turbulence more than not running a muffler would do because they eliminate the backdraft effect (or so I read). Without the proper documentation, I believe that this conundrum is up in the air as well.


I wonder if anyone has any dyno runs of their single and dual exhaust systems. If you're going to change your exhaust, take a dyno run before and after so we can see the change. It would be greatly appreciated


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## 20v master (May 7, 2009)

Chuckmeister87 said:


> Thank you TTcK
> 
> 
> Someone from the Porsche community


Stopped reading here. Porsche = Boxer 6 cylinder engines = two banks = doesn't apply to 1.8T's. If you think dual's are better, go for it. If you think it's the best performance option (not sound quality, looks, etc), then you're wrong. To support your "claim", and I use the term loosely, why don't you fab a custom exhaust that splits immediately after the turbo or where ever you can find room to split it as close to the turbo as possible, and keep them split all the way out to the rear valence, and dyno it for us. You can't take general blanket arguements about other engine layouts and apply them to a completely different engine. Next think we know, you'll be posting dynos supporting X pipes from a Mustang saying "Look, it makes the power better at these rpms." Tempest nailed it, we're all being dragged down. :banghead:



Chuckmeister87 said:


> If you're going to change your exhaust, take a dyno run before and after so we can see the change. It would be greatly appreciated


What would this prove? Would the single system be left as is and a second exit added? Or are we replacing the entire 60mm 180Q single setup with a 2.5" 225 setup, which has a completely different muffler? Or are we comparing two aftermarket setups, one 2.5" with a 2.5" with two exits? Are we talking two mufflers or one with dual outlets? Or are we splitting the outlet of one muffler to two tips? I hope you're understanding that it's not just as simple as "single exit vs dual exit." IF you don't, then you're lost and too hardheaded to listen to those that understand physics, heat transfer, and thermodynamics.


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## PLAYED TT (Oct 17, 2010)

I can't believe this is still going. Why would splitting a single exit exhaust give you more power? Someone explain this to me please


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## Marcus_Aurelius (Mar 1, 2012)

Bob, it's funny what you posted is *almost* evidence of what I'm stating and the proof that Chuckmeister is hopelessly looking for. I'm quoting myself below to refresh on what we have on our cars (unless of course we are talking about a V6 TT here). 



Marcus_Aurelius said:


> I'm not sure you fully understand what you're arguing. We have a single bank of cylinders, a single manifold, single turbo leading to a single hotside and downpipe.


In your search to rationalize the ingrained misconception, you came up with a dyno graph of a 928 GT. The dual bank of cyliders should be looked at as two seperate engines linked by a single crankshaft (at least in terms of exhaust flow). If it wasn't for the fact that the flow of the two cylinder banks were also merged, this would be usable data to our discussion. Here are the specs for that car:


engine code	M 28/47
cylinders	V 8 in 90° vee
capacity	5 litre
4957 cc
(302.495 cu in)
bore × stroke	100 × 78.9 mm 
3.94 × 3.11 in
bore/stroke ratio	1.27
valve gear	DOHC 
4 valves per cylinder 
32 Total valves
maximum power output
(ece)	329.5 PS (325 bhp) (242.4 kW)
at 6200 rpm
specific output
(ece)	65.6 bhp/litre
1.07 bhp/cu in
maximum torque
(ece)	430 Nm (317 ft·lb) (43.8 kgm)
at 4100 rpm
specific torque
(ece)	86.75 Nm/litre
engine construction	
sump	
compression ratio	10:1
fuel system	Bosch LH-Jetronic fuel injection
bmep (brake mean effective pressure)	1090.1 kPa (158.1 psi)
maximum rpm	
crankshaft bearings	
engine coolant	Water
cylinder volume	619.63
aspiration	Normal
compressor	N/A
intercooler	None
catalytic converter

It's a V8 with two banks of cylinders and two manifolds. In that particular case, keeping the exhaust flow from each bank in two seperate pipes would be beneficial, if you were looking for ideal conditions. In any case this does not apply at all to a 1.8t *4 cylinder*. :beer:


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## Marcus_Aurelius (Mar 1, 2012)

Chuckmeister87 said:


> Thank you TTcK
> 
> 
> Someone from the Porsche community actually recording the changes rather than sit back on "what should be, and here is the science to prove it". There very well be some variable you forgot to take into account, Max, or something you just completely did not expect in which you can then explain scientifically. You don't just use THEORY and say it's correct without the proper documentation. I do not question your vast knowledge you have obtained relating to horsepower and handling, but you simply need evidence.
> ...


*"performance mufflers have been designed to even out the pulses that exhaust exits in"*
:laugh::laugh::laugh: 

Where do you even find this stuff, or you just make it up?

* "Many mufflers decrease turbulence more than not running a muffler would do because they eliminate the backdraft effect" *

:laugh::laugh::laugh: You are seriously too much for me handle, I have to rephrase everything I write 10 times so I it doesn't sound too insulting as it's not my goal... but you seriously make it too easy. At this point I'll let you have this one -- YOU WIN! AND MY QUOTED SIG IS IN FULL EFFECT :wave:


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## 20v master (May 7, 2009)

Wow, I didn't even read all that. Decreasing turbulence and eliminating backdraft? AKA eliminating scavaging? :banghead: He's clearly set in his beliefs, no matter how poorly they supported. :screwy:


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## TTC2k5 (May 23, 2008)

Marcus_Aurelius said:


> Bob, it's funny what you posted is *almost* evidence of what I'm stating and the proof that Chuckmeister is hopelessly looking for. I'm quoting myself below to refresh on what we have on our cars (unless of course we are talking about a V6 TT here).
> 
> 
> 
> ...


As I pointed out in my post, it was not a 1.8. But the point of that discussion is that 1 is not greater than 2 when the source (in this case 2 manifolds/8 cyl) of the exhaust is joined to form one source (like our 1 maniforld/4 cyl system) into a single exhaust system. His dyno data indicate that 8 cy dumping into a single source is not more efficient than 8 cy dumping into a dual exhaust source. It also points out that when you increase the cross sectional area/exhaust capacity by increasing pipe size, performance increases. 

You can continue to accuse me of rationalizing misconception if you choose, but I'm just trying to learn, like others here, rather than just drinking the kool-aid.

cheers


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## 20v master (May 7, 2009)

TTC2k5 said:


> As I pointed out in my post, it was not a 1.8. But the point of that discussion is that 1 is not greater than 2 when the source (in this case 2 manifolds/8 cyl) of the exhaust is joined to form one source (like our 1 maniforld/4 cyl system) into a single exhaust system. *His dyno data indicate that 8 cy dumping into a single source is not more efficient than 8 cy dumping into a dual exhaust source. It also points out that when you increase the cross sectional area/exhaust capacity by increasing pipe size, performance increases.*
> 
> You can continue to accuse me of rationalizing misconception if you choose, but I'm just trying to learn, like others here, rather than just drinking the kool-aid.
> 
> cheers


Is the single source the same size as the dual source piping? What size initial to what size after increase shows a gain? What if you keep increasing the size? There is a point of diminishing return, you know? I made 470FWHP through a single 3" exhaust (no muffler or cat) that terminated right before the rear axle. Adding a muffler, a split, more piping, and/or extra tips would in no way add any power, and would only lower the power output level. Engine size, engine layout, engine architecture, space for said exhaust, and user preference all play a role in determining exhaust size. If you want maximum performance from a transverse 1.8T with a single turbo, you don't need a true dual exhaust or even dual tips exiting from a single muffler, as evidenced by Max's single setup making more power on a K04-02x than anyone has ever documented. The fact that we're debating dual vs single, both coming from a single muffler, shows that no one here really intends to run a true dual system on a 1.8T. We're really discussing dual tips from a single muffler vs one tip. If you wanted maximum obtainable power from only changing exhaust and were willing to sacrifice, you'd have a short 3" pipe sticking out of your hood or fender for the shortest distance possible with the least number of bends. /thread


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## Marcus_Aurelius (Mar 1, 2012)

TTC2k5 said:


> As I pointed out in my post, it was not a 1.8. But the point of that discussion is that 1 is not greater than 2 when the source (in this case 2 manifolds/8 cyl) of the exhaust is joined to form one source (like our 1 maniforld/4 cyl system) into a single exhaust system. His dyno data indicate that 8 cy dumping into a single source is not more efficient than 8 cy dumping into a dual exhaust source. It also points out that when you increase the cross sectional area/exhaust capacity by increasing pipe size, performance increases.
> 
> You can continue to accuse me of rationalizing misconception if you choose, but * I'm just trying to learn*, like others here, rather than just drinking the kool-aid.
> 
> cheers



I'll enter this discussion once again because you say you're trying to learn and there might be others like you. 

1) You were on the right path when you brought up cross sectional area. To effectively evacuate the exhaust pulses (remember we have force induction and don't need any back pressure) without killing the velocity of the exhaust gases (this could happen if you go too big in diameter or piping cross sectional area to be technically correct), you need a certain piping diameter. This required piping diameter is dictated by a host of variables -- the main ones being the engine displacement, volumetric efficiency, turbo size, and boost pressure. Once that minimun pipe diameter is determined (whatever it is), the next goal is to evacuate gases using that piping without creating turbulence and restrictions. Turbulence and restriction is exactly what any bend, split, muffler, and additional length of piping creates. So in layman terms, the less of that you have happening, the more efficient and powerfull your system will be. 

2) This brings us to the next point: what cross sectional area or piping diameter is needed for our car?
There are no simple answers because there is more than one variable, and we all operate at different pressure ratios and are closer or farther away from ideal volumetric efficiency. So in a nutshell, the minimum piping requirement for a stock TT will be different/less than what I need to evacuate 35-37 psi with more exhaust byproducts generated by E85. Decades of empirical testing of all sorts have shown that 3" diameter is sufficient for most 4 bangers turbos (except the extremes). For example, in my case, I am at the edge of diminishing returns and may soon benefit from a 3.5" or 4" system. This far, keeping the required minimum cross sectional area throughout is the only factor worth looking at. Once you introduce a crush bend for example, you reducing that ideal cross sectional area and reduce overall efficiency and power. This is why we gain power from an aftermaket exhaust with nice mendrel bends that keep the cross sectional area intact. Now, every bend, split, has the same effect as a crush bend.

3) without really thinking about it, one would assume that it doesn't matter if one pipe or a pair of pipes provides the cross sectional requirement. It would seem so at first, but a deeper analysis would also reveal that the overall length of the piping also have a detrimental effect. On top of that, a turbulent split is required at some point, and two major additional bends are needed to package all this for our our platform. Anyone looking at this would clearly see that two bends, several feet of extra piping, and a split (possibly an extra muffler) will inevitably have an effect on efficiency (and definitely not an improving effect).


As pointed out by many, the cool aid here is "one = good --> two = gooder"! You can be the judge of who is drinking it.


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## PLAYED TT (Oct 17, 2010)

20v master said:


> The fact that we're debating dual vs single, both coming from a single muffler, shows that no one here really intends to run a true dual system on a 1.8T.


This is why I'm wondering why anyone is arguing over this at all:screwy:

So to fuel this bs argument even more someone needs to run an exhaust with 4 tips on that Porsche to see what the gains are :laugh:

EDIT: Threads like this make me wish there was a :middlefinger: emoticon :banghead:


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## 20v master (May 7, 2009)

Screw it, I'm going to put a 3rd tip on my dual tip setup. :facepalm:


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## jbrehm (May 16, 2006)

I came here to prove a point with some physics, but decided to be immature instead. 

Yeah, _everyone_ in this thread is missing the real point! If two is better than one, then three is better than two, then four is better than three, etc. Personally, I can't think of anything that would unlock more horsepowerz in my car than adding 150lbs of metal, 16 x 90° bends, and about 20 more feet of piping!

Moar tips = moar flow:


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## PLAYED TT (Oct 17, 2010)

Lmao


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## TTC2k5 (May 23, 2008)

Marcus_Aurelius said:


> I'll enter this discussion once again because you say you're trying to learn and there might be others like you. ...
> 
> As pointed out by many, the cool aid here is "one = good --> two = gooder"! You can be the judge of who is drinking it.


Already did my friend, already did.

cheers.


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## Tempes_TT (Oct 24, 2010)

Well, Im going to take a stab at this and see if I can shed some erm...light. 

It seems to me we have a few different concepts going here and are getting quite confused. Forget numbers, forget physics, thermodynamics and theory. Lets go back to the first grade. 

*Chuckmeister87*, You seem to be fighting towards the general idea of duel exhaust. Which when applied correctly, yes, two exhaust pipes are better then one. *When applied correctly.*

Max, along with the other geniuses of the forum, are fighting towards the idea of *one in, one out - single exhaust.* *All arguments based on our specific application*

Now. We are in a car specific forum, with 75%+ of its members having the same motor... a 1.8t 4 cyl engine.

In my books, there are two terms that are being interchanged with exhaust.

*Dual Exhaust* and *Dual Exit*. Two very different things... 

Now I made us a pretty little picture (dont judge me, I was bored) Mind you, Im no engeenier, theorist, thermodynamics master... Im just a regular 22yr/o guy who likes to play with cars...Let me illustrate 










As I stated before, We are in a car specific forum. To bring the general concept of dual exhaust to a single exhaust application and argue that two is better than one when "application" is of no consequence, is simply absurd. 


Our TTs have...

One bank
One exhaust
One exit.

Thus the conclusion to this argument is that One in, one out is indeed best *for our application* when best possible performance is the goal.

:wave:


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## ttwsm (Feb 27, 2011)

Now that is a picture that's worth a thousand words! I think it gets to the heart of this crazy thread.

:thumbup:


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## Chuckmeister87 (Nov 10, 2009)

Listen, I got the idea behind the difference between the Porsche and the TT before Max even posted about it. I'm well aware of it's setup it was running yet the difference between having dual exhaust or single (as long as the single was wide enough) wasn't very much. For our cars, I really doubt there would be a big difference in performance between dual and single port exhaust.


Being a genius doesn't make you infallible, so provide dynos if you please. Simple request


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## ttwsm (Feb 27, 2011)

But I must also say that I dig the dual-tip systems where there's a valve, like a while back on STT_V6's car. When open, it allows the straight-through exit out one tip. When closed, it directs the exhaust across and through the muffler to the other tip for stealth operation. Kinda cool.


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## PLAYED TT (Oct 17, 2010)

ttwsm said:


> But I must also say that I dig the dual-tip systems where there's a valve, like a while back on STT_V6's car. When open, it allows the straight-through exit out one tip. When closed, it directs the exhaust across and through the muffler to the other tip for stealth operation. Kinda cool.


But in that case why not have a butterfly at the end of the down pipe and make it an open dump?


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## 20v master (May 7, 2009)

PLAYED TT said:


> But in that case why not have a butterfly at the end of the down pipe and make it an open dump?


That's Much Mo Better for a turbo engine. :thumbup:


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## 1fast2liter (Apr 4, 2005)

screw it i am just gonna remove my dp and exhaust and run it straight from the turbo.... yea boi.


i think adding any system to our 180s is better then running the stock lincon log size pipeing. in sayign i went with a modified 225 exhaust cause it was cheap easy and right their.




i agree with everything max has said. and the wasted space of a post about duals proves nothing on a 4cyl application. sure i went with a single exit exhaust in my dodge ram. the changed it out to duals with a gibson xpipe exhaust muffler. i think when i dynoed it i gaind about 18hp over all and about 13tq. when i added the longtube headers is were i got the greates gains... if i am not mistaken you said performance mufflers decreace scavaging like it was a good thing in my experiance the more scavaging a system can do the more exhaust thats pulled from the system the more power you can make. as i stated before cars like the mustang come from the factory with duals on a h pipe. the test that was writen about was done on a v8 i fail to understand how it implys or even is related to a motor that runs half the cylinders and is turboed on top of that.

inplied runnigna stock turbo at stock levels probably not gonna be a huge deal what you run but start pushing it to the max and wanting to get as much as you can then youll start looking at exhaust and what makes or breaks you... as stated what makes since the straightest pipe that end asap or a pipe thats twisted kinked bent and ran every wich way. it will take more pipe when all is said and done to exit the same place as the straightes pipe would. personaly i love the dual look. i kjnow i dont make tons from it and i am not out to make a ton of power at this time. 


ill say it now max you have been a huge help so has alot of others on here. all one has to do is look at what max drives.. yet people still feel the need to tell him hes full of bull &h!t. i say let your results speak for them selves. 

in so saying going with the logic here would that mean the new ttrs with the 4 tips flows more then as it has 4 exit points?:facepalm:


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