Hi all, I just purchased for my 2008 5.4L F150these longtubes:

http://www.stage3motorsports.com/08F...ct-System.html

As well as this muffler:

https://www.carid.com/borla/proxs-st...mpn-40348.html

with these tips:

https://www.carid.com/stainless-work...pn-795250.html

The y pipe on the midpipe is 2.5" to connect to the factory system. I planned on running into the Pro XS muffler 2.5" and exiting 2.5". All this should be arriving to my house soon, so if it's a good configuration I want to stick with it. But I know many people run 3" back. I currently have a true dual 2.5" with X pipe and oval Maggies. Should I return the Pro XS 2.5" center inlet/ dual outlet and replace it with a 3" center inlet, 2.5" dual outlet and run 3" from the Y to the muffler? Will 1/2" larger pipe from the Y to the muffler create THAT MUCH of a noticeable difference in sound and low end on a N/A motor? if it's not majorly noticeable, I think I'd rather stick with what I have than go through the hassle of returns and such. That being said, if 1/2" difference will greatly improve sound and low end power, i may have to swap the mufflers. Even if I should run 3", how can they safely stretch the Stainless Works Y pipe to 3" right to where the left and right side tie in as 2.5"? Wouldn't there still be an area it comes together as 2.5" that couldn't be stretched, so there would be a small choke before it bumps to 3"? Thoughts? Real world experience? Thanks in advance.

Ryan

 

I just went thru this exact situation. I installed a maggy 2.5" in 3.0" out Y pipe and ran into my 3" Borla XR-1. Then another Y pipe to dual back out to 2.5" to Harley exits.
I like the single 3" and good for mid range power, but I also plan in the future for cams and possibly S/C so I'm leaving my options open. A single 2.5" "should" net you the best low end performance.
Now with all that said. With LT headers, and single 3" I didn't notice much of a low end loss. Look at the new f150s all are 3" stock

 

x2. Keep the 2.5" if all low end torque possible matter. Otherwise, 3" center pipe makes a good deep growl and feels pretty strong still. I have a similar setup as lariat02 posted, minus the headers and Magnaflow muffler.

 

I'd say just keep the 2.5" if otherwise it's gonna stay near stock.

I recently replaced a MF series 40 which was a 3" SI / 2.5" DO muffler and it had two 2.25" tail pipes to rear, the front pipe you describe was a "not pretty" muffler shop bent 2.5" pipe .... from the OEM rear end of the 2.5" SS pipe from Y. I added a 2.5" 28" long glass pack ahead of the FM back in 2009, no change in power or mileage, just made it some quieter & mellower.

I replaced it with a similar style muffler, in May 2016 using a kit with a 3" SI / 2.5" DO chambered muffler and 2.5" OD tail pipes and a 3" OD intermediate pipe from Y back to muffler inlet (it was necked down to 2.5" at front end). After awhile, I bought and installed a 3" ID stainless steel glass pack ahead of this one as well to reduce noise and to mellow it out .... which it did.

As to power & mileage ... there was no difference between any of them that I could measure with a stop watch from 30-70 on a same roadway or in MPG from my gas stop in Greeenville to home and back. The changes brought about by my swapping / adding glasspacks dealt with noise quality, quantity, and replacing rotted aluminized steel with stainless steel.

I got a far bigger change for the good from my FP 1865 Tuner using the 87 tune. Mine also has a CAI & 3.55 rears.