I have a 05 Lariat and I want to put an exhaust on it, but my main concern is low end torque. What is the best setup for low end torque. Would just a muffler swap with the stock pipes provide better torque than a larger catback? I see that a lot of the systems are 3" but I don't see what the benefit would be going to a larger pipe after the factory y pipe. After that bottleneck it seems like enlarging the pipes would cause a decrease in velocity and temperature creating a more turbulent flow.... am I way overthinking this?

I guess what I am asking is: Will doing a catback instead of a muffler swap benefit low end torque any?

 

If you want sound only, then just do a muffler swap to something you like. The cat-back has very little benefit over the stock. The restriction in the OEM muffler and Y pipe is what kills your low end.

The absolute best setup for low end torque is going to cost you a bit, 2.25" true duals X piped with straight through mufflers, FULLY mandrel bent.

There is no such bolt on kit, you would have to find a shop that would do mandrel bending.

The benefit of going 3" off the Y is slightly stronger torque, not much, just lsightly, and a better, more deep tone.

 

So going up to 3" after the 2.5" y with a catback would help low end rather than hurt it? I don't quite get it, but almost all of the kits are 3" or 3.5" and they all say they increase low end so I guess theres something more to it. Perhaps the increased pipe size is more about increasing the inlet size on the muffler for less restriction than actually increasing flow before the muffler....

 

Its only worth converting to the 3" Y if you have an unrestricted Y pipe made, or buy the Magnaflow one, its only $27. Increasing the midpipe size when getting the better flowing Y pipe equals things out, and is healthier for future add ons. Good way to go if every bit matters, and if you dont want to true dual in 2.25".

 

Let me make my recommendations based on personal work with the 4.2 V6 and the 5.4 V8, with the emphasis on low end torque.

With the 4.2, I usually remove ALL of the exhaust system from the manifolds back. I use 2.25" tubing to 2 Magnaflow 94305 cats (1 on each side), then use 2.25" tubing to a Magnaflow 10758 dual 2.25" in/ single 2.5" out Y pipe, to a 2.5" in/2.5" out muffler (Magnaflow 12216), and 2.5" piping over the axle and exiting at a 45 under the right taillight or straight out, both with turndowns at the end.

Wtih the 5.4, I usually use the same looking system, but go with 2.5" tubing from the manifolds, 2 Magnaflow 2.5" in/out cats, a dual 2.5'" in/ single 3" out Y-pipe, a 3" in/3" out Magnaflow muffler, and 3" piping to the exit.

As far as running duals, I DO NOT recommend them for a low end torque situation. But if you would like to try them on the 5.4, replace the dual 2.5" in/3" out Y pipe with a dual 2.5" in/ dual 2.5" out X pipe, dual 2.5" mufflers, and 2.5" piping. As for duals on the 4.2, I would eliminate the X pipe and run 2.25" in/out mufflers and piping to the exit points of your choice.

Again, I do not have experience with the 4.6, but I would tend to offer the same advice as I have for the 4.2 would work for the 4.6 in a low end torque situation.

The biggest bottleneck in the stock exhaust system is the poorly designed Y connection that the drivers side has to go through on ALL Ford truck engines. The second problem is the stock muffler is rather restrictive.

P.S. Another thing that will increase low end torque is a good programmer. But that is a WHOLE OTHER can of worms that I will not open in this thread.

 

on my 04 5.4 super duty van- i went from the oem 3" siso to a ss mandrell bent x piped 2.25" dual exhaust,i already had my tuner prior to this- went back to tuner on dyno- fyi no adjustments were needed, i make well over 300 rwftlbs tq and it stays there to a shade under 4k rpms from a peak of 320 at 2k,very contradictory to what you advise- i tow 5,500 lbs every weekend from march till nov, and the dyno doesn't lie either-if i dropped even a hint of tq-that oem exhaust would have been on in a heartbeat...ui'm all about bottom end tq.

 

Openclasspro#11, I noticed 2 differences between what I used on a dual set up and your set up.

1. You are using 2.25" piping instead of 2.5" piping. This should increase low end torque. Also, mufflers have some bearing; the dual system I worked with used Flowmaster Deltaflow 50s (what the guy wanted, not my choice). That, I felt, killed part of the bottom end torque.

2. Programmer. Unfortunately, the guy with the 5.4 I helped did not have a programmer and was running a stock tune.

Another thing with the 5.4 with duals that came to mind was how poorly it seemed to run at the time the duals were put on. It seemed to be weak from some engine problem (no codes), but it "felt weak". Later, his transmission failed.

Like many have said before and I will repeat, your experience may be different than mine.

 

Those 3 things will definitely have an adverse effect on low end torque:
1) 2.5 inch pipes
2) Sl... I mean Flowmaster's
3) Failing transmisson

 

2.5" isn't the most healthy to true dual on a N/A modular. Its been proven. Some are lucky and never tow and can live with it, until they lift it and find out how bad the 35s hold them back.

But seriously, why did you have to mention the transmission failing part....

 

When I was reading on exhuast upgrade for my 06, I read that the best exhuast set up on are trucks is to go with a 3" pipe after the Y single in dual out muffler and high flow cats. I done that set up and I love it. I can chirp my heavy 285/50/20 wheels so I know I did not lose any torque maybe the tune help out alot. Lots of people have diffrent set up's, so there will be diffrent opinions.

 

I love my 2.5" duals, and can still turn my 18" nittos over.