I'm interested in mapping out the stock exhaust on my 4.6 F150 so I can figure out what to do to it and where I should put it all. I'm interested in the a torque INCREASE, just like iron horse, and I'm thinking so far of just doing a muffler swap. However, I would like it to look good as well as sound good.

I'm going to kind of talk it out here, from the headers back, and if I mess up, don't hesistate to correct me. I'll italicize things I'm unsure of. This is for a '02 4.6 V8


Stock exhaust manifold, combines 4 cylinders into one 2.5", creating one pipe for each bank.

  |
 \|/ 2 2.5" pipes

Catalytic Converters - 2 on each pipe (4 total), one after another, maintaining a 2.5" pipe size. I assume the reason for two cats on each pipe is for different operating temperatures.

  |
 \|/ 2 2.5" pipes

Y-pipe - 2 2.5" combined into a single 2.5" pipe

  |
 \|/ single 2.5" pipe

Extension pipe - 2.5" to get from the Y-pipe back to the muffler

  |
 \|/ single 2.5" pipe

Factory muffler - 2.5" SI, 2.5" SO

  |
 \|/ single 2.5"

Tailpipe, 2.5" regular pipe. Not mandrel-bent


I haven't found any good pictures of most of this stuff. If you've got pictures that you can pull, maybe just crawl under there and snap a few for me, I'm going to be constructing a gigantic flowchart soon.
The eventual goal of all this is kind of like a huge FAQ. I know I've asked the same questions that a whole bunch of other people have asked as well. The website could stick it up or something, and that way, we could just point towards the FAQ instead of answering the same questions over and over again.
If you're interested in support (and hopefully helping) with a FAQ, especially you exhaust gurus, please don't hesitate to email me @ InfamousTim@neo.tamu.edu. Hope to hear from you people soon, as well as corrections to my somewhat crappy-looking map.

 

My factory exhaust culminated into a single 2.5" pipe exiting the Y-intersection; not a 3". My intermediate pipe and the muffler inlet were both 2.5"; not 3". So, my whole system was 2.5". There was also a substantial inner restriction where the driver's side pipe hit the Y-intersection. Inside this connection was 1&3/4".

 

Really? I can't believe they would restrict it THAT much at the Y-intersection ... crappy design is all I can say. I was guessing at the pipe sizes mostly. Thanks for the input.

 

Yes, really !! From looking at the "outside" of the Y-intersection, the driver's side attachment looks fine. In reality, upon attachment, they chop out a jagged, uneven hole in the passenger's side pipe and butt weld the driver's side pipe over this. This leaves an inner restriction that leaves 2.5" of driver's side exhaust slamming into an under 2" hole, while the passenger's side pipe has a full 2.5" (wonderful design ...NOT). This is extremely poor flow engineering. You want smooth transitions, not your exhaust farting through a jagged, washer like wall....LAME-OOOO !!

 

So, I guess the next step would be to figure out at every part along the system, what kind of backpressure is being created? The ultimate goal would be create some kind of pseudo formula for what to change and where. That'd be just awesome. We could say "You want a 3" pipe? Ok, well, do this and do that ..."

What I'm looking at doing is replacing the factory Y-pipe and the factory muffler, but leaving the rest. I might end up with headers later on down the road, but that's after some other mods as well, where I need to eliminate even more backpressure.

No takers on a mini-FAQ? Come on, men, rally yourselves!

 

Infamous Tim-

I was reading that you may want to swap out your muffler. Ths is what I decided to do after hours of research. I went with the Flowmaster 40 original series muffler and left the stock pipes on it. I had the shop put a 3" diameter 8" tip on the end. I too did not want the loud sound and amazingly this is the rifght s ound I wanted. Not loud by any means and there is almost no in cab res. This is due to the fact that the muffler location is back under the bed. I originaly thought I wanted the 40 of 50 Delta Flow but after listening to the set ups that would have been too soft. Currently I will not wake anyone up with this muffler on. I have noticed better gas milage and also no loss on low end torque a gain on top end torque. The guy at the shop recommended the 40 original because if you just swap out the muffler the Ford's run 4 cat's and that is overkill as it is. Anyway, I am really happy so far and hopefully this helps you out.