Single vs. Dual Exhaust - Ford Forums - Mustang Forum, Ford Trucks, Ford Focus and Ford Cars
Ford Forum Ford Forum

» Auto Insurance
» Featured Product
ยป Wheel & Tire Center

Go Back   Ford Forums - Mustang Forum, Ford Trucks, Ford Focus and Ford Cars > The Garage - Tech Forums > Exhaust
Register Home Forum Active Topics Photo Gallery Auto Loans Garage Mark Forums Read Auto Escrow

FordForums.com is the premier Ford Forum on the internet. Registered Users do not see the above ads.
Reply
 
LinkBack Thread Tools Display Modes
Old 05-09-2006, 21:41   #1 (permalink)
Registered User
 
Join Date: May 2006
Posts: 2
Single vs. Dual Exhaust

I have a stock Ford 5.4L in a 2004 Expedition. I've been getting about 13.8 mpg with it and the power isn't nearly what my 5.9L Durango used to be. In addition, I'm now pulling a boat with it so I can use more lower end torque.

I'm adding an Airaid cold air intake and a new exhaust system to it but am hearing conflicting opinions regarding pipes. Some people have said that, for pulling the boat and more low end power, I'm better off going with a single in, single out Flowmaster system with 3" pipes. Others have said that no matter what, more flow is better and I should go with a single in, dual out system. One guy today said that, with the single system, I'm getting three inches of flow whereas with the dual, I'd be getting five inches of flow.

So, the question is, for better mileage and better pulling power, which system is going to be better - the one that's more restrictive (more backpressure) or the one with better flow?

Thanks,

Doug
sunburninaz is offline   Reply With Quote
Sponsored Links
Advertisement
 
Old 05-09-2006, 22:34   #2 (permalink)
Registered User
 
Freshmeat's Avatar
 
Join Date: Sep 2005
Location: Geismar, LA, USA
Age: 31
Posts: 833
Re: Single vs. Dual Exhaust

All in all, more exhaust gas flow produces more horsepower. However, more exhaust gas velocity produces more torque. It's all about a balance (stay with me as I try to explain).

Let's look at what will be REQUIRED for you to do this exhaust system and still pass emissions, for starters:

Functional Catalytic Converters (at least two or three, depending on stock design).
Muffler that is not uncomfortably loud.

Now- for catalytic converters, a lot of people have had good luck with the Catco brand. For the price, they're probably your best option. They'll provide better flow and, in many cases, better fuel atomization than stock equipment. You'll have two O2 sensors between the exhaust manifold (or header) and the catalytic converter (one on each bank). This will read the initial oxygen levels in the gases exiting the combustion chambers.

Then, the gases get to the catalytic converters. After passing through the cats, they'll hit your second sensors, often called wide band sensors, which also read oxygen levels, but on a different scale. They'll expect the mixture to be different because of the extra gases burning in the cats. Without cats, your sensors will throw a code, tripping your MIL (Malfunction Indicator Light). So- we know you'll need some good cats to get the job done, but without running a more free-flowing design, you won't see as much improvement from your exhaust system.

For your muffler, find something that will keep a low note. I've heard great things about the MagnaFlow mufflers. Stainless steel is always the way to go, especially if you'll be launching boats- the aluminized steel will rot away in no time, trust me. There won't be enough difference between one muffler and the next when you're looking to put it on a daily driver. MAYBE 1-3 horsepower, but I'd much rather sacrifice that 3hp and have an exhaust tone I can handle instead of going all out and getting headaches from the exhaust being too loud. Again, spend the money on stainless steel. It's worth the cost now, because you won't need to replace it later.

As far as what size pipes to use:
FLOW = HORSEPOWER
VELOCITY = TORQUE
That may throw you off at first. Let me explain: With more room for the gases to flow, you'll get better horsepower. It flows more freely with an open (wide) exhaust, so it's better for a higher horsepower band. However, you want torque, so you want to shoot for velocity. Torque is produced by the velocity (or speed) of the exhaust gases passing through the system.
If you have the same amount of gases flowing through a 3" system and a 2.5" system, the gases in the 2.5" system will travel at greater velocity, because there's less room for it to expand. Instead of expanding out, like it would in a 3" pipe, it can only expand forward and backward. It's NOT going back into the engine, so it can only expand forward, so that creates velocity. It's a lot easier to design an exhaust system designed for horsepower gains as opposed to torque gains for this reason.

Now- with all that said, I would personally recommend you run this: Clicky
It's designed for low-end torque, while the only other bolt-in stainless steel set-up (which was actually MagnaFlow) appeared to be designed more for horsepower (MagnaFlow had a straight-through design, as opposed to Gibson's chambered system). There is an aluminized steel assembly, just like the one I linked you to, but aluminized parts only carry a 90-day warranty, whereas Gibson keeps a lifetime warranty against corrosion and rust-through on their stainless steel systems. Again, let me say- it's worth it. I'm about to rebuild my entire exhaust system after making the mistake of running Flowmaster's aluminized mufflers (only a year and a half ago) because they've already rotted inside and rattle.

I'd say get the system I referenced (you can bolt it on yourself) and if you want more performance, take it to a shop and tell them you want to replace from your manifolds to the system you bought and you want to run the same size pipe as what's on the new equipment. Make sense?

I hope this helps you out. Didn't mean to write a novel, it's just not that easy to explain how much difference an exhaust system can make on performance. Good luck and let us know what you decide.
__________________

My Garage
Freshmeat is offline   Reply With Quote
Old 05-09-2006, 23:11   #3 (permalink)
Registered User
 
Join Date: May 2006
Posts: 2
Re: Single vs. Dual Exhaust

Thanks for the quick response. In terms of what you state:

If you have the same amount of gases flowing through a 3" system and a 2.5" system, the gases in the 2.5" system will travel at greater velocity, because there's less room for it to expand. Instead of expanding out, like it would in a 3" pipe, it can only expand forward and backward. It's NOT going back into the engine, so it can only expand forward, so that creates velocity.

OK, so... I understand that the gas will flow at a greater velocity in the 2.5" pipe as opposed to the 3" pipe. What about TWO 2.5" pipes? Will this effectively equate to the velocity of a 5" pipe (are we going to get into physics here?)? In other words, if I go with the single in, single out system, I'll likely use 3" pipe. If I go with the duals, it will be with 2.5" pipe. How will these two compare to each other in terms of gas velocity - and similarly - in actual terms of gains? In other words, can I expect a 10% gain in torque with one and 5% with the other? I realize this is a highly subjective question but on the off chance there is an answer I thought I'd ask...

Thanks again,

Doug
sunburninaz is offline   Reply With Quote
Old 05-10-2006, 19:16   #4 (permalink)
Registered User
 
Freshmeat's Avatar
 
Join Date: Sep 2005
Location: Geismar, LA, USA
Age: 31
Posts: 833
Re: Single vs. Dual Exhaust

I was hoping you wouldn't get into that. Because, yes- it involves physics.
Here we go...
The surface area of a 2.25" pipe is effectively 3.9760782021996".
The surface area of a 2.5" pipe is effectively 4.9087385212341".
The surface area of a 2.75" pipe is effectively 5.9395736106932".
The surface area of a 3" pipe is effectively 7.068583470577".
It's better to deal with surface area than diameter, for several reasons. It gives a better idea of how much the gases are capable of expanding ******d.There's a significant difference between the 2.5" and 3" sizes. If you run a single 3", you'll be better off than running two 2.5" pipes (7.068583" of surface area as opposed to 9.817478" [almost a full 3" of surface area]), unless you're looking for the horsepower.

So- bottom line, if you're going to run either single 3" or dual 2.5", go with the single 3". You'll produce significantly better bottom end torque than with the duals. In fact, most of the local Mustang guys I know are ditching their dual set-ups for single 3".

Do the hard numbers help you any more in making your decision?
__________________

My Garage
Freshmeat is offline   Reply With Quote
Old 05-17-2006, 19:52   #5 (permalink)
Registered User
 
Join Date: Jan 2006
Location: Tioga, LA, USA
Posts: 148
Re: Single vs. Dual Exhaust

I'm impressed with your knowlege oh freshmeat, so I will now pose to you another question: How does exhaust play a role in fuel economy/efficiency? Also, what role does the x pipe play in all of this?
redneckf150 is offline   Reply With Quote
Old 05-18-2006, 08:04   #6 (permalink)
Registered User
 
Freshmeat's Avatar
 
Join Date: Sep 2005
Location: Geismar, LA, USA
Age: 31
Posts: 833
Re: Single vs. Dual Exhaust

Fuel economy is a side effect of the exhaust system. When you build the system properly, it'll increase the efficiency of the motor, thus (hopefully) increasing fuel consumption, because it isn't trying so hard to get moving.

The X-pipe is a more radical design than the H-pipe. While both allow for cross-flow scavenging of the exhaust gases, the design of the X-pipe makes it scavenge much more efficiently. This seems like a good thing, but then taking backpressure into consideration...

More scavenging = less backpressure
X-pipes are only really good for Mustangs and muscle cars in general because they'll be pushing the power to a level where the scavenging would be noticed. A larger car (or truck) would be best with an H-pipe because the increased backpressure would help move the large vehicle around.

Does that answer your questions?
__________________

My Garage
Freshmeat is offline   Reply With Quote
Old 05-18-2006, 18:11   #7 (permalink)
Registered User
 
Join Date: Jan 2006
Location: Tioga, LA, USA
Posts: 148
Re: Single vs. Dual Exhaust

So, when do you need a cross-pipe of any kind (including straight). Also, how does 2 into 1 (or other combinations) fit this model?

I'm not trying to test you, I am just very interested in exhaust physics. Been trying to find the right exhaust for my Harley as well as my truck, so I can use all the information I can get.

Thanks
redneckf150 is offline   Reply With Quote
Old 05-18-2006, 21:04   #8 (permalink)
Registered User
 
Freshmeat's Avatar
 
Join Date: Sep 2005
Location: Geismar, LA, USA
Age: 31
Posts: 833
Re: Single vs. Dual Exhaust

What do you mean by 2-to-1? Other combinations? I'm feeling like absolute Hell, so try to be more specific for me, please.

It's best to incorporate a cross-pipe whenever it can be fit. It's one thing to design an exhaust system to route the gases away from a vehicle... it's another thing to design the exhaust system to enhance the performance of that vehicle. So, yes- use a cross-pipe whenever you can fit one (but you only need one).
__________________

My Garage
Freshmeat is offline   Reply With Quote
Old 05-18-2006, 21:05   #9 (permalink)
Registered User
 
Freshmeat's Avatar
 
Join Date: Sep 2005
Location: Geismar, LA, USA
Age: 31
Posts: 833
Re: Single vs. Dual Exhaust

The funny thing is, I never took physics. Only passed my high school math and science classes because I cheated.
__________________

My Garage
Freshmeat is offline   Reply With Quote
Old 05-19-2006, 05:13   #10 (permalink)
Registered User
 
Join Date: Jan 2006
Location: Tioga, LA, USA
Posts: 148
Re: Single vs. Dual Exhaust

What I'm talking about is this: This is my understanding so far...on one end of the spectrum, if you want the most HP gain, you would have large-bore exhaust with one continuous pipe from each cylinder to one exhaust pipe. On the other end of the spectrum, if you wanted the most TQ gain, you would have each of the cylinders routed into one modest combined exhaust system. Do I have the right idea, or what?
redneckf150 is offline   Reply With Quote
Sponsored Links
Advertisement
 
Reply

  Ford Forums - Mustang Forum, Ford Trucks, Ford Focus and Ford Cars > The Garage - Tech Forums > Exhaust



Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Powered by vBadvanced CMPS v3.2.2

All times are GMT -7. The time now is 06:06.



Powered by vBulletin® Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Content Relevant URLs by vBSEO 3.6.0
Garage Plus vBulletin Plugins by Drive Thru Online, Inc.