I recently put shorty headers on my 2002 4.6l f150. There are two very short pieces of exhuast pointing towards the ground so I could plug in the front 2 o2 sensors so I'm basically running open headers right now. I have a 2 1/4 xpipe going to a 2 in 1 out flowmaster 50. I'm going to have the back two banks plugged into the exhuast just before the xpipe. People say backpressure is bad but i'm not so convinced. My truck has no lower end now. Should I put my cats back on or will the xpipe and the muffler make the low end perform better? (exluding the fact that 2 o2 sensors aren't plugged in)

 

In case that was worded in a confusing manner the muffler and xpipe have not yet been installed.

 

Without catz your illegal in the usa. To go to all the trouble why not just dual it all the way back with an H pipe ( balance ) tube for economy and mileage. There are a lot of extravagant designs to a simple exhaust out the back with 2 nice sounding mufflers. Even running the 2 along side each other out the back. The more you put into it the more it costs. Stainless would be my first choice for a lasting job. Had a 409 with simple pipes and mufflers separate from each other and the car flew. Not one problem except keeping it full of petrol. Drove it a lot and bought a lot of gas. It wasn't a family car though.

 

Back pressure is a myth and theres a very informative sticky about how exhausts work its under the engine talk section.

 

Unless it is of a much smaller diameter or the bends are badly crafter, I don't think it would ever add any restriction.

 

+1 to this…

from my experience x pipes are installed to equalize pressure between the 2 sides...

 

There's a reason this is a sticky in this section:
https://www.f150forum.com/f11/exhaus...re-myth-78102/

 

It's more about your camshafts and duration. If you like the hard lope of a highlift with the extended pull of higher rpms than the extravagent exhaust pays off. For day to day and dirt road applications stock is more than better.:scoote r: My 4x4 cammed and dualed with bigger intake valves, ports matched gaskets and polished with flo tests, and dual exhaust, it would do 100 mph in low side of transfer case. Changed out the High Lift intake later for better torque around town streets and hills. Otherewise the truck never got out of 2nd. gear.

 

Here's the reason I'm asking. I have open headers right now and my bottom end is completely gone. My powerband FEELS like it kicks in at 4500rpm's. lol Kinda useless for driving down the road. From what I've read you don't need back pressure if you are driving a dragster. This is not a dragster lol. Maybe I'm wrong about that, correct me if I am please. I already have an x-pipe and a 2 in 1 out muffler bought.(I've been pulled over twice I want it quiet) Gonna run the pipe out the back like a stock exhuast. Not worried about cosmetics just making it a sleeper. So since I've already bought the xpipe should I buy cats or not? Not worried about legality cause I live in Oklahoma. I'm getting ready to put a new intake manifold on and stage two cams if that makes a difference. Please give me input or correction if I'm wrong about said things in this paragraph

 

You never need backpressure, street or strip. The reason the open headers have moved the power band is because there isn't a long enough run for scavenging the other cylinders to take place at lower rpms. Once you get into higher rpms there is less time needed to help scavenge the next cylinder because the gases are still in the system when the other one is on the exhaust stroke. At lower rpms the gases from one cylinder are far enough gone to not help the next, so that cylinder has to exert more force to push the gases out of the cylinder into the atmosphere.
It sounds like you've got it pretty well put together now, X pipe as close to the front as possible, muffler as far back as necessary, and size your pipe correctly and it'll be fine.