I currently have a Borla Catback exhaust. I recently bought a set of 2 chamber Flowmaster mufflers for my mustang which I decided not to put on. So I want to put them on my F150 and split it off to true dual exhaust. Will I benifit in horsepower and torque? Or will it not have enough backpressure, causing me to lose horsepower and torque? Thank you.

 

Well true dual exhaust is having a separate pipe for each side of the engine. This would not be legal and you would be VERY lucky to get a shop to do it for you. Plus doing so would decrease your backpressure too much. Your best bet...dual it off after the cat and then put one muffler on each pipe and send out the tailpipes where you want. A good custom shop should be able to do this for no more than $200 with stainless steel tips. Should give you a nice sound without much....if any power loss. Neither myself or others have never had a problem with this setup.

 

As long as you keep your O2 sensor in there, you should be good to go. If you really want to open it up, you could add a high flow catalytic converter, it would get you closer to a trual dual setup in that each pipe has it's own space. Get two pipe in, two pipes out for the cat, then a flomaster or whatever with two pipes in/two pipes out, then out the back. I like the way the dual exhaust sounds, as for power, well, thats questionable. I believe there is a fine line between when you get more power and start to lose it. I'd like to think Ford engineered their trucks to be powerful and economical and that the setup they have is optimal, but alas, this is not the early 70's, so i don't think they did. So you may have to play experimenter/engineer for the exhaus system. Either way it will sound better.

 

MN4X4, just asking, no flaming intended, but if you had a cat and a muffler on each side, why would it be illegal? I personally would think it better with an X-pipe, but just wondering why true duals would be illegal? I don't understand...

 

So-called true duals really need to be connected together with a balance tube which is simply a section of pipe which is welded from one exhaust pipe across to the other to equalize pressures and sounds. Check with your exhaust shop on this and I think you will find that it is the recommended way to go. It also makes for a stronger system that will not move around after installation. Aside from this, you can make a separate exhaust for each bank. make sure the oxygen sensor is relocated to the left bank when the new system is installed (they may have to weld in a bung for this.

 

Marv1, you mean like an H-pipe?

 

It is not that the duals are illegal, per se, it is that 'tampering' with the pollution controls, which include the catalytic converter, is illegal. Yes, it is possible to have true dual catalytic converters but before such stuff can actually be installed, it must be approved by the gov't. Thus, a shop which dreamed up its own version of duals all the way back would be tampering, unless their mods had received gov't approval, and that is why it would be illegal.

 

It is not the back pressure, per se, that messes things up, it is because the resonance of the pipes have changed and that harms scavenging.

Consider the simplest case, a straight pipe. Each time the exhaust valve opens, a pulse (sound wave) travels down the pipe. This wave or pulse has low and high pressure components. When the pulse reaches the end of the pipe, a reverse pulse is generated that travels back up the pipe. Make the pipe exactly the correct length for a given RPM and you can time the pulse so that the low pressure component of the pulse reaches the exhaust valve at the time it opens. This low pressure helps suck the exhaust stream out of the cylinder. If you make the pipe the wrong length, then you might have the highest pressure point in the return pulse arrive when the exhaust valve opens. Then, you would harm scavenging and lose power. This is why headers of exactly the same length generally help performance.

Real world pipes are much more complicated. For one thing, we operate at multiple RPM's and thus, no pipe length is perfect for all RPM's... it is a Hobson's choice to choose the best overall length. Next reverse pulses are generated not only at the end of the exhaust pipe, but at every bend and at every point that the diameter of the pipe gets larger or smaller. Add in the fact that you have 8 cylinders all putting their pulses into the exhaust pipe and things get real complicated.

Exhaust designers use many tricks to enhance the scavening effects of the reverse pulse. This includes megaphones to reduce pressure and create a reverse wave, constrictions to create reverse waves, crossover pipes to take advantage of the pulses of other cylinders, and the placement of baffles in the muffler and converter to cause a reverse wave to be generated. The trick is to get all the pulses that are generated all over the exhaust system to line up in such a way, across all RPM's to maximize the low pressure scavenging pulse at the exhaust valve.

Building a good exhaust system is as much art as science and I'll bet Ford has spent 10's of thousands of hours trying to maximize the scavenging effect. Based upon my experience with motorcycles, and from the comments here of people who have added aftermarket exhausts to their trucks, there are very few aftermarket exhaust systems that are well enough designed to avoid a power loss. Some of the most popular pipes for Harleys rob 10 to 15 percent of the available power just so that they look and sound nice. Ditto for the Cobra pipes so popular on the Valkyrie... 6 to 10 HP gone to get that 6 into 6 look. On the other hand, Two Brothers Racing makes pipes that add 5 to 25 HP depending upon application because their pipes are designed right.

Before I were to buy any aftermarket pipes for my truck, I'd want to see some dyno runs from the pipe manufacturers, but I'll bet you can't get them because the news would be mostly bad.

 

If you do it right, power everywhere! If you do it wrong, you will lose bottom end.

Here is how we do it in Oregon:

Get a flowmaster DI/DO 50 series (3 chambers for us older term guys). Cut the Y off, run 2.25" pipe (yes, 2 1/4", not 2.5") back to the muffler. Put a equalizer pipe 8-12" in front of the muffler at 1.5-2" in size. Then after the muffler, run the pipe out the side before the rear wheels. Jarrod, Chris and I am next doing this. They gain power from idle to WOT. Sound is excellent! jarrod has the dual Si/So flows, but the Di/Do of Chris's truck sounds a LOT better. Plus the Di/Do is much cleaner to install. Myself, I got a muffler from a lightning, so that I what I am going to install.

 

HI!... I have a TRUE duel exhaust system on my truck. Back preasure is very critical on these trucks. A lot of people make the mistake of using a VERY high flow muffler or 2 chamber FLOWMASTERS. The key is to use a 3 chamber FLOWMASTER and have all pipe s "MANDREL" bent. My system is all 2.5 inch mandrel bent using FLOWMASTER straight in, straight out 3 chamber 'RACE" style mufflers. I picked up low-end and top end power. Read my lower SIG. you will see what my truck runs with this set-up.

 

Neal,

Do you use a X or H pipe with your set-up? What type of flowmasters do you suggest? (part numbers?)

 

HI!... BLKF150LARIAT : No I don't currently have a "H" or "X" pipe installed in my system. I'm going to fabricate a totally new system with JDM long tube hedders, high flow cats (2) and a "X" pipe with all mandrel bent stainless steel tubing. I'm installing a custom fuel cell soon and will no longer have the factory steel gas tank in my way. I'm going to have the dual tips exit out like the LIGHTNING on both sides of the truck. Sorry I lost my bill, I don't have the part#'s for my flows.

 

The truck already has 2 cats on it before the Y-pipe, so the cats or the O2s will not be touched. I was planning on running 2 1/4" piping to each muffler and 2 1/2" pipe out each muffler. I wanted to use 2 chamber flowmaster mufflers b/c thats what I have to work with brand new. So should I go with this setup or just leave the borla alone? Thanks.

 

Sounds like a good plan to me STWater...utilizes what you have and you shouldnt lose any power and may actually gain a little.

PickupMan...
BeastRider has it right. Any tampering with the emissions controls (i.e. coverters and o2 sensors) when they do not need repair is illegal. Im not sure of the specifics but have heard that when a shop has to replace a converter they need to file paperwork and what not to prove that nothing is being modified from stock. Even my exhaust guy who owns his own business and works by himself in a small MN town will not modify anything between the motor and cats with exception of smog-legal headers.

The only way to have a true dual setup is if you have the know how and tools to do it right. And even then you might lose power plus have trouble with emissions testing (mandatory in some states, was eliminated here in MN about a year ago.)

BTW PickupMan...no offense taken!

 

MN4X4 and BeastRider, thanks, that's much better than what I had!