I went to a local truck accessories shop to price a hitch and electric brake controller. While I was there I talked to the guy about eventually doing some performance upgrades on my 07 STX 4.6L that I just got last week. I told him I wanted true duals with the tailpipes in front of the rear tires with an X-pipe. He said I'd loose too much backpressure even with a 2.5" piple. He suggested doing a 1 into 2 flowmaster and exit out the back. The gas tank would be in the way to exit out the left side and there would be too much pipe to curve around the tank. I haven't looked under there yet so I don't know what it looks like. Am I getting straight talk here and would I be better off with a 2 into 1 system? I do haul a small RV and bought the truck for a bit more power over my V6 Sport Trac.

 

Hey Figstr, try posting this in Aftermarket Intake & Exhaust systems. You'll have better luck there.

 

I dunno about your question regarding routing the pipes, but I do know that you will lose backpressure with 2.5" true duals and thats going to hurt your lowend torque.
Id go with single-in/dual-out muffler if you want the look and sound of duals.

 

You are getting the truth. You could run true duals but you would need 1.5" pipe more than likely. I would just do what he recommends.

 

running true dual with x pipe and 2.25" tubing and he will not lose-phil

 

Yep.

And he's right about the gas tank being in the way and routing under and around it. Go straight out the back or angled out the back.

 

I did true 2.25 duals (no x pipe) with stock cats and thrush glasspacks and my butt dyno says I gained power all over.

 

1.5" pipe LOL... Your not going to loose that much if you do an X pipe, you really should get 2.5" unless you want that raggedy sound...

 

When you take away back pressure you might gain horsepower with true duels but you when loose torque. Both are very important. I wanted the most of both. You can put true duels on but you have to equal out both sides of pressure and slow the flowdown. I know you would think that freeing up flow would be better but, the 5.4 and 4.6 are designed to have back pressure to make horsepower.

 

It is NOT backpressure, not at ALL. It's all about the correct sizing for the pulses to pull each other out. ANY back pressure will cause HP loss, whereas also a too large diameter pipe will cause a LOSS IN PRESSURE and will CAUSE HP LOSS.
See this: https://www.f150online.com/forums/sh...d.php?t=298027
ALSO, when you run duals, it is NOT completely the same. The size of pipe I have in that link is for SINGLE, not dual.
2.5" dual is about the equivilant of 3" single.
The area inside the circle grows differently than what we're used to with squares (lengthXwidth doesn't work for circles) and therefore the area that the exhaust has to go through doesn't grow the way it is normally thought.

Back to the question at hand though, an example.....
Think of a bunch of tennisballs going through your exhaust pipe. All you have to do is push on the back one and they all push out the other side, right? This is the idea with exhaust. With a bigger motor, or a motor with bigger mods etc. you have bigger tennisballs. If you have a smaller diameter pipe, they have to squish through the tight area, and you lose power. This is what most poeple understand just fine.
Now, with a properly sized pipe, the tennis ***** will fit just snuggly into the pipe, and when you PULL the last ball out, it will creat SUCTION, sucking the next ball out with it, and that pulling the next etc.

Another way to think about it is a counter weight. If you have to move something, and have a counterweight, a little push will make it travel with less effort and much further. Each exhaust pulse going down that pipe is essentially a counterweight, making the engine work less to travel the same distance (in this case the piston distance).

Lee

 

Oh, and H pipes and X pipes are a whole nother ball game altogether.
Basically, they will all work within moderation (no 4" duals plz) so go for something within reason and what sounds good to you.

Oh, and I won't go into it here, but engine speed is also a factor as well as higher rpms will need more pulses going through at a time than lower rpms.

 

That's off there buddy.

A 3" single circle (single 3" exhaust) is 7.065 square inches in area.

Two 2.5" circles (2.5" dual exhaust) are 9.9125 square inches in area.

Two 2.25" circles (2.25" dual exhaust) are 7.948125 square inches in area.

As you can see, that a big difference there. 2.5" duals are WAY too big for our N/A 5.4 trucks. I do agree it's exhaust gas velocity that is important, not back pressure. And yes, you need a h or x-pipe to balance out exhaust pulses (your tennis *****).