I had read a few posts stating the best pipe for the 5.4 was either 2.25 or 2.5. I went and had my exhaust system installed today. I went back to the place I purchased my Dynomax for my 98 F-150. I remember they were great in that they actually held up 4-5 different options and let me hear them. Once again the customer service was great. I explained what I was looking for and he suggested 3" pipe. He personally liked the Dynomax because he prefers quite. He stated the Dynomax units are not welded and do not hold up as long, but overall he would chose it. He understood I was looking for a nice sound while starting and getting into the throttle. I ended up choosing the 50 series Flowmaster with the Delta Flow Technology. I questioned why tyhe 3" pipe and he said with me having the K&N intake system, he felt the 3" was the best choice. He has over 30 years experience and I took him for his word. I wanted to see what people think about the pipe size? As far as performance... it sounds great and the truck seems to fly. You must remember I'm used to my 98 w/4.6 and 285's on it. The sound is nice and loud on the outside, but I have to put the windown down in order to hear inside the cab. I think my next and last performance inhancement is going to be the Hypertech III. I like the idea of being able to choose between 87-92 octane. The dyno's state 45 HP gain on the 5.4. I have no idea how accurate this is, but it sure sounds good!! Anyone have any opinions on the Hypertech with the 5.4? Thanks for all help!! You have any fishing questions... I'd be happy to help you out. If you're in the Sacramento, CA area around Sept-Oct, call me up and I'll hook you into some 30+ pound king salmon!! Fish on!!

 

Here's A link to a tech page that might answer some questions.

Good luck.

 

3 Inch all the way back, There are some other pics in my gallery.

 

Stock 5.4L Engines:
Based on experience, if it were me, I'd run 2.5" to maintain my low end SOTP for single-out systems, and no larger than 2.5" for dual-out systems. But then again, that's my opinion.