I have a 2006 F-150 5.4 ext. cab. I already have a flowmaster catback exhaust on it and I am thinking about putting on long tube headers. So all I want to know is if true dual exhaust is better than just a catback when you have headers put on???? Just would like to know the performance gains from both sides..pros and cons thanks for your time

Flan

 

You will notice no gains from the true duals, if anything, you would loose bottom end power. Any good catback should give you great sound and great performance. It also costs less and weighs less. True duals really won't give you a meaningful benefit unless you can keep both sides equal length, which is almost impossible with the gas tank in the way.

 

I really dont see how a true dual takes away bottom end power no offense I think that is a load of bull

 

You loose the benefits of exhaust scavenging. By having the exhaust combine together in the right way, you can create a relative vacuum that gets more of the exhaust out of the cylinders especially at low rpm. While we could dispute this for a great deal of time, and probably not convince anyone, one point that is hard to disregard, is that if the dual exhaust does not have equal lengths, it will not function or sound like one that does. It also costs more to build and install, and it weighs more, possibly nullifying any power gains. If done correctly, a dual outlet muffler, referred to by some as false duals, can project more sound than a true dual with comparable mufflers.

 

You're talking about going with a single out, or duals with an x-pipe or h-pipe in it, correct?

 

An h-pipe helps equalize the exhaust a bit, and an x-pipe is a great way to go if you use true duals. It helps overcome the low end torque problem, and in my opinion, makes it sound better too.

 

on a ford truck if u run true duals on it u run the two pipes on the passanger side u souldnt have a probem depending on the mufflers u want to use, i did it with my old truck and it gave me some extra power when i needed it plus it also sounded great,i used glasspack on mine

 

I agree completely with you Bear River! The only time true duals should be used, is on a built motor, thats pushing 500 hp, and is running a carb! But thats my opinion...

 

ran 2.25" true duals .ss mandrell bent piping ,x pipe in original location of oem y pipe,magnaflow mufflers on my 04 5.4.low end torque went up quite noticebly on the sotp dyno as well as on the dyno,true duals DONE RIGHT will yield excellent results

 

If you compare two similar systems, such as a 3.00" single versus a 2.25" dual system, the dual exhaust has 44% more drag per linear foot that the single 3" exhaust. The reason for this is simple. In a dual exhaust, you've got more surface area (the tubing wall), than in a single system. This wall also acts as a way for the exhaust heat to escape. When the exhaust heat escapes through the tubing, the exhaust slows down. This slowing creates backpressure. In a single system, there is less contact with the tubing walls, so less heat is lost per foot. These two simple facts conspire against dual exhaust systems.

This is without taking into effect the benefits of a properly designed y. In a dual exhaust, these y-s are absent. Let me explain how exhaust flows, so that you can understand the benefits of a y-pipe, because without knowing this, you will never understand how a y-pipe can be beneficial.

When the exhaust flows out of the cylinder and into the port and then down the primary tube in the header or manifold. During this phase the exhaust is under pressure and is also still burning and expanding. As a result, it gains significant speed. Like all matter, gases have mass, and when in motion, also have inertia, and they want to keep moving once put in motion, and to resist changes in motion. When the exhaust valve closes, these gases are still in motion, and because they don't wan to stop, they will leave a relative vacuum wake behind them. But this wake does counteract and slow the motion of the pulse as it travels down the exhaust. The longer this wake is left unfilled, the more the exhaust pulse will slow down. If it slows down, it will create backpressure. When the gases enter a y-pipe, the Bernoulli principle comes into effect and the motion of the other exhaust pulses comes into effect. The Bernoulli principle is simple, but I won't go into it here. Look it up in Wikipedia. The rapid motion of the exhaust flowing through the y-pipe will create a vacuum in the opposite end of the y. the exhaust will also enter the y following another exhaust pulse,filling the vacuum left behind that pulse and reducing the drag on the preceding pulse. The result of these effects is that the exhaust will experience less resistance as it travels down the tube. Now if the y feeds into a pipe of slightly less than the combined size of the tubes that feed into it, the exhaust will pick up speed as it passes through the y pipe. This speed will further enhance the scavenging effect. If all o this is done right, the result will be less backpressure at the head, and this means more exhaust will escape from the engine, and that means more fresh air and fuel can enter the engine.

In a dual exhaust these systems are absent. Yes there are y-s or collectors in the headers or manifolds, but you are missing the benefit of the final y in a single system. So the exhaust pulses have to fight their own vacuum wakes the entire time they travel down the tube, and you don't get the extra boost from the Bournouli principle as the fast moving exhaust travels through a y-pipe. An x pipe helps, but the problem with the x pipe is that the exhaust is expanding into a larger area than it came from, so it slows down and cools, and so the bournouli effect is not as strong as that found in a properly sized y-pipe. It is better than duals without an X-pipe, but not by much.

The reason the bottom end suffers is because at low rpm, the exhaust is not moving as rapidly as at higher rpm. Because it is not moving as fast to begin with, it slows down much more quickly, creating backpressure. It is also not as hot, so as it looses heat, it slows down even more. As rpm increases, the exhaust pulses follow each other more closely, and that causes them to pick up more speed, and the scavenging effect becomes more prominent as the vacuum becomes more powerful.

Now you don't have to take just my word for it, there are plenty of cases in the industry where the principles I am talking about are being used to make better products. Top end header manufacturers are making triple y-headers, which produce more top and bottom end power than long tubes or short tubes. They do this through the Bernoulli principle. JBA has developed their "Firecone" collectors which merge the exhaust into a slightly smaller area to make the exhaust pick up speed as it passes through.

I would seriously have to question your claims on power gain. No doubt you have more power, but have you compared it to what you could have had? And did you get a power reading before you did that, and have you done a comparison against the factory system with a better muffler? There are a lot of variables here, and the idea in science is to take them all into account.

 

you also forgot to mention that ss is better for heat retention for scavenging purposes,my truck-an 04 ford van came with 3" siso oem from the factory,the before and after dynos from the same day on the same dyno do not lie,my van weighs ~9000 lbs loaded and i pull a 14x7 trailer dual axle `~5000 lbs with it-not taken dyno numbers into effect,if for one minute tq was lower,that oem would have been back on in a heartbeat,money is not the problem ,bottom line improvement is,you seem to know a thing or two on exhaust flow,explain to us how using the static regain method is utilized with velocity pressure in tubing then...

 

The question is, can you actually tell if you have more power. Its easy to confuse sound with power. I had my Mazda with a 3" intake, and it made it much louder, and to me it seemed to be more powerful. But after doing some 0-60 runs, I found it was almost 2 seconds slower. After I had a new intake built (in part because I broke a piece off that was not easily replaced) I had it built according to the velocity theory. My new intake, instead of being 3" is 2.25". It also has a longer run. The results were astonishing. A hill I used to have to take in 4th gear with the pedal to the floor, could now be taken in 5th with up to 1000 lbs of stuff in the bed. The method does work. Now this may not seem to be directly relevant to the exhaust, but actually many of the same principles come into effect here too.

But on to answer the question you seem to be asking lets get a few things straight. Yes, stainless steel is a poor conductor of heat, and does give better heat retention. However, the factory system uses stainless steel too. So there are no gains in materials between a factory system and your dual exhaust in terms of the materials used. But I do recommend the stainless, and if stainless is not used, heat wraps should be used if heat retention is a concern.

The factory system sucks. Ford, like all the automakers, is trying to compromise between the cost of doing it right, and the mass production. So they do cut some corners. The worst corner they cut is that horrible factory muffler. So just by changing the muffler out, without doing anything else will gain enough power that you will notice, and this will be both top and bottom end power. Better flowing cats (the factory ones are bad, but they aren't great either), can open up some top end without effecting the bottom end. By better flowing, I mean more cross section and less linear catalyst. The factory cats have about 8"+ of catalyst lengthwise, which creates some backpressure at higher RPM. Most years also have pre cats, which adds another 4". Our 1000 series cats have 4" of linear catalyst, plus the added benefits of more cross section, which overall reduces the backpressure and improves the power output slightly. The factory system also has a poorly thought out y-pipe that does not join the gases smoothly, and that prevents them from scavenging properly. A stamped y-pipe you be better, or some carefully constructed welded units that put some emphasis on the way the air flows through it.

So the way to utilize the setup properly is to first find out what the ideal size is, which is most often a function of the engines displacement. For most gas engines from 5.3L - 6.0L, 3" is acceptable for a single system, but 2.5" will work well too. 2.75" is the best for the 5.4L, but that is a hard pipe size to come by on anything other than factory systems. The pipe ahead of the y should be around 2.25", though 2.125" would be better. The y-pipe should direct the air in the proper direction, and should blend the air gradually, and should neck down slightly before flaring back out to the desired exhaust size. A really complete system will use a triple-y header, since that enhances everything else, and is independently proven to enhance the entire powerband. The factory cats can be used, but larger bodies ones can compliment everything else. In fact the cats can actually increase bottom end power. As the exhaust passes through the catalyst, it will heat up, accelerating the gases through the cat. The exhaust will end up moving faster after the cat that before, creating a positive scavenging effect which can enhance bottom end power further.

 

i disaagree on the muffler being the weakest link in the system-the ford oem y was horrible where the driver's side merged into the passenger's side-went 3/4"into it,also did my homework with my exhaust,the 4 oem ford cats flow pretty well,installed an in cab magnahelic gauge tapped into 2nd set of 02 sensor bungs, and took some 2nd gear runs to redline under load up a hill and it was neglible to change out o high flows cats, did this at tailpipe on oem 3" as well as at tailipipe on my 2.25",these readings as well as my peak torque being at LOWER rpms on the dyno vs my oem system support my claims,as well as putting my van up against the other 7 that i own,0-85,walks away from them,maybe there was a reason fomoco runs 2.25" duals with x pipe on their mustang gts than 3" siso

 

You are telling me you were able to tap and measure backpressure at the exhaust ports?

I am not doubting that your true duals are better than the factory system. I would agree, the stock y was awful, but have you seen the inside of those factory mufflers?

The reason for runs duals on the Mustang is because very few people would buy them if they didn't. Running duals with factory mufflers is probably better than running singles with factory mufflers. Those OE mufflers are awful in terms of airflow.

 

found a fitting that threaded into back set of 02 sensors ,then used fitting that went into that that, converted it into a barb fitting,1/4" pneumatic tubing ran into cab where i had magnahelic gauge,then just used o2 sensors bungs attached at 1' from end of tailpipes for system backpressure reading