02 F150-7700 4x4 with 5.4L. So far the only mod has been removing the intake air horn. I took it off to try it and promptly ran over it backing out of the garage, so its off for good. I'll likely replace it with some PVC just to go back to getting cooler air from the fender.

One manifold is cracked, the mid-pipe is pretty rusty, the muffler has a massive hole, and its time to re-do the whole thing.

No reason to go nuts. The goal is to fix what is busted, so I see no reason to 1) go back to stock drinking straws, nor 2) go crazy with removing all the cats, a tune, and using $500 headers just to get 15 hp that I'll never feel anyway.

I heard from a few sources that the Dorman manifolds like to crack and/or warp frequently. True, or just hype?

Any shorty smog headers I should be considering?

Does hacking out (or gutting) the downstream cats require tune/hack or fouler mod to prevent SES? I understand its the downstreams that are more restrictive? (by the way, I live where there is a visual and plug-in emissions test, but no sniffer)

My basic plan is; replace manifolds with Dormans or shorties, keep the cats but maybe gut the downstream cans if there is a compelling reason to do so, and then have a shop fab up some 2.5" side-exit duals with mufflers I haven't picked yet.

Suggestions? Critiques? Ideas?

 

Here's a suggestion for fixing your intake:

https://www.f150online.com/forums/ar...3-f-150-a.html

I'd use stock manifolds, a pair of high-flow cats with bungs for the rear O2's, and whatever you want behind them.

 

I actually have some leftover 3" PVC from when I did that mod to my 98 4.6L. It is happening this weekend.

Any truth to the rumor that the Dormans crack and/or warp?

 

I don't see how they would be any worse than the stockers.

 

Some people on another forum were complaining that they warped and/or cracked very quickly. One person reported a 1" crack at 19k miles. They hadn't even had time to get surface rust on them.