Firstly, thanks for a great write up with the exhaust guide I've read it and re-read it, but I'd just like to ask some questions before I go to the exhaust shop and tell them what I'd like.......It's on a 2003 5.4 4x4 Expedition (2v motor)

I like the idea of true duals, and I don't need cats here, so was thinking of having them all removed and using the o2 spacer mod (I thought I'd need to leave the 2 fronts for back pressure etc.... until I read the sticky) - as I haul a heavy travel trailer (toy hauler) I need as much torque as possible, and would like a nice loud sound, without too much drone - so if I go true dual, I'll probably get the tips at 45 degrees at each corner, or maybe 90 degrees so the sound doesn't bounce back of the front of the trailer.

So, if I go true dual, and don't have any cats, should I use the 2.25 tube so I don't loose torque? and again for torque, I assume the H pipe is better than the X pipe?

And another question:o if the true dual works out too expensive, or there are other reasons not to get it - can I remove all cats, space the o2's, and run 3" tube ok?

Any advice appreciated! I know I want the best of everything, good sound, more torque, no drone, and not too expensive

 

Since you do tow I would strongly suggest staying away from true duals.

Stick with with a Y pipe and do a SIDO setup. This will ensure you don't lose any low end.

I went from true duals(x-pipe) on my 2002 5.4 back to a Y pipe and felt a noticeable gain in torque down low.

 

Great, thanks for the input, that's the kind of thing I was wondering about..............

So, if a SIDO would be better for towing, would a SISO be better still? (basically what I've got, but would loose the cats and have smaller muffler)

 

I agree for towing, keep it a single 2.5" system. Dual tips look good and will work in this application as well.

 

I think you are on the right track staying with a single pipe for bottom end. I put true duals with an H pipe on one of my trucks, and I think I lost a little bottom end as well. I like the sound, but for pulling, it probably wasn't the right choice.

 

OK, I had the truck in a shop today to look at the options of the exhaust, and it looks like I'll need to keep with a single outlet, as there doesn't look enough room to dupilcate what is already on the passenger side (factory)

So, back to the drawing board, and could do with a bit more advice please! As I'm going to have to keep to SISO, should I go for a cat back system (something like Magnaflow?) to keep it simple, but then at the front, cut off the second cats, leaving the first ones there for now, and route the front cats into a 2.5" Y pipe (2.5" dual in, 2.5" single out) - or is it best to run the dual pipes from the cat into a muffler with a single outlet (didn't know if you can use a SIDO the other way round?)

Or, should I go larger diameter out, and get a shop to copy what I have, justin larger bore, something like 3" from the muffler??

Thanks for any help - as you can probably tell, Im having to learn as I go with this!

 

Here you go man...

First off, yes you can go duals. It will just look like this...



I still recommend sticking with a SISO for MAX low RPM torque.

NOW, Lets start with the cats. Remove the rear cats as you stated. Then run 2.5" pipe from the remaining cats directly into a 2.5" in/out Y pipe. From there you need to keep it 2.5" to the 2.5" SISO muffler of your choice. After the muffler you can either keep a single pipe to the exit of your choice, or use a second Y pipe here to run a dual exit.

As far as 2.5" or 3" SISO goes? Here is the deal. If your are doing a lot of towing and you want the lowest torque curve possible, then run a 2.5" SISO period. A 3" system will still do well, but it will raise the torque curve some. It will also sound a little better/deeper in 3".

As a side note, I will add... For a stock engine, duals are for sound ONLY! Even a 2.5" dual system will hurt your low end torque if your towing. It is noticeable. For just daily driving duals are perfectly okay. Now if you have a forced induction engine, duals in 2.5" or 3" is healthy. The extra volume in the pipe allows the engine to produce more horsepower. In a naturally aspirated engine, the extra volume in the pipe reduces exhaust scavenging that builds your low end torque.

Hope this helps.

 

Thanks avfrog, it's good to get some input from someone before I ask them at the shop to do something I don't fully understand!

There was room for the duals ate the front and mid section, it was where it goes over the rear axle to exit that there wasn't really enough room for twin tail pipes - although, it sounds like I'm best to go for the SISO like you said anyway.

Do you think I'd gain or hurt it by removing the front cats also? It would be easier for fitting to leave the fronts in, as the pipe could be cut at the straight section between the two cats, then run to a y pipe (the stock system on mine runs the two 2.5" from the rear cats into one 2.5", but its a horrible y section, that basically squashes each 2.5 in half - where something like a Magnaflow 2.5" y section looks a lot better flowing)

Thanks again, I appreciate it, as there aren't many of these trucks here - I've only seen a couple others on the road in the 3 years I've had this one!

 

Went from the oem 3" exhaust on my 04 e 250 with 5.4 .I tow every weekend from march to Nov ,approx 5,500 lbs.my van is damn near 9 k lbs loaded { Hvac contractor},torque is What I need. Almost 400 k miles ago I had my 2.25" stainless,mandrell bent ,x piped exhaust installed with 14x 9 magnaflow mufflers,my low end torque went up,if I lost any torque,that oem exhaust would have been back on in a heartbeat,when done correctly, you gain torque with a dual exhaust.my .02$ ,Phil

 

For an Expy, I suggest a stainless catback JBA, 3" SI/SO. That's what I run, don't feel I've gained much aside from a killer sound but no loss of power. When I had it off, straight pipe, a loss of power was noticed.

 

You probably gained the extra torque by removing the restrictive OEM muffler. You would gain more torque if you ran a single 2.5" and a free flowing muffler.

 

Since when frog? All I've ever seen is 2.25" true duals are the best on these vehicles n/a.

 

Not for the lowest torque curve possible needed for towing. There is less volume in a single 2.5" than dual 2.25". This increases low RPM scavenging for MAX low torque.

 

Thanks again guys, like I said there are hardly any of these trucks here (or F150's) - and after reading the 'exhaust guide' on here over and over, I'd made up my mind to have true duals..........but then the feeback from people that have these engines definately seems to look like for improved torque a SISO, or SIDO would be better than the duals

I hadn't realised how little room there is under the truck - upto the rear axle is fine, there's plenty of room for it to be dual'd, but then from the muffler it goes over the axle and through a gap of the chassis and body, to eit after the passenger rear wheel - and on the drivers side, that gap has a lot of pipes in the way - so this combined with what people are saying about torque, I'll try a SISO, but made a lot better than the OEM!

Ideally I'd love it to sound like a Mustang I had a short ride in a GT500, and the sound alone made me want to own one! (think I'll have to wait until the kids are grown up though!)

 

There's a reason why shortsighted vans and f 250&350 ran 3" vs 2 1/2" in e & f 150s,lower egts,they know they were going to worked harder