Has anyone installed headers on a V8 ?

I'm in the middle of an install and have a question about fitting the cat to the header and welding.

Thanks

So what's your question?

Long read but there's lots of good info about install from about this page on in this thread.

Interest in Custom built 4th gen V8 4.7 Doug Thorley Headers

Hi Blackoutt.

Hey BTW I'm up in the Fort Wayne area. How far south of Indy are you?

Anyway my question is:

Now that I have disassembly complete, the weld flange on the header is about (and I'm guessing on these sizes because I don't have it in front of me at the moment) 2 3/4 and the inlet on the cat is about 1 3/4 - 2. It looks to me like they will weld together on the taper of the cat body. Is that correct? I know the cat is still the same size as factory but it seems awful restrictive.

I am considering a cat delete but I am concerned about noise as it's my daily driver. Which way did you go? Factory cat, aftermarket cat, or delete?

Thanks,
Kent

I'm in Columbus so not local at all lol.

Header is 2.5" and stock y pipe is a 2.25" flange they say but yes pipe measures much smaller. Doug Thorley instructions show where to cut the stock cats but I just built a jig and had a friend weld extra 2.5" pipe and flange on for a bolt in install, no fitting and tacking on the truck. If I were to do it again I'd reduce it to 2.25" pipe and use a smaller flange to it would make to stock or URD y pipe better.



The delete changed the sound a bit with a flowmaster 50 muffler that I had before but I like it, even for a daily, it's still pretty mild. The headers themselves are louder than muffled stock manifolds which I'm a bit dissapointed in but that's just the nature of larger tubular headers. The power and and hopefully the fuel economy gains will be worth it.

I finally got them done. I decided to go with Magnaflow high flow cats. All turned out well. I was hesitant to do it but I decided to cut off the air injection tubes and tig weld them shut. I had previously disabled it AIP so that wasn't an issue. What a difference this made for installation. I had both headers installed and torqued in under 30 min. I would definitely recommend it for anyone that isn't scared to do it and has or will take care of the AIP.

NICE. I wish I would have cut my AIP tubes off and welded them too but left it to allow the opportunity to go back if need be (not that there's ever a reason to go back). My only complaint so far is the new headers sound ticky which I've read about tubular headers sounding that way more so than cast but coming from our stock tube manifolds I didn't think it would be this bad. I thought I might have leaks but it's the same warm vs. cold and don't see any evidence of exhaust blowing out around the flanges, retorqued everything, no change.

Mine is a little ticky but I have to get my ear down by the wheel to hear it. Still sounds better than the tractor sound with both manifolds cracked. Cats may dampen mine a bit too. The rest of my exhaust is stock and it sounds completely factory. Be a couple months before I complete the rest. I'm going to post up some tips in the long header thread, when I get time, for anyone going the DIY route.

I also have O2 sensor question with the headers. Should start a new thread or is there one going that I can look at / post to?

I can hear mine when I'm driving up next to another car or curb or something, kind of annoying but the exhaust sounds nice. Mines louder with no first cat and a flowmaster muffler, no resonator and side exit tip. The rest of the piping is stock though.

What's your O2 sensor question? Might as well ask it here.

Any thoughts on replacing the factory y-pipe? Eye-balling the system you can tell it's a bottleneck.

It's a huge bottle neck, I thought the 2.25" flange meant it was 2.25" wrong it measures like 1.78 inside there. I asked URD about how their flange would mount up to my 2.5" flat flange but they just kept telling me it would mount to stock headers which was not my question so due to being unhelpful they are out. I don't like relying on other people so it'll be a while til I get annoyed enough to take it to a shop to have one built lol. I don't want to get rid of all the backpressure either, this isn't a big boosted race car so I'm not sure what my ultimate plans are there, leave it for now. You can even hear my ticking in the open header video though so I know it's the headers.

Maybe Blackoutt will chime in. Not sure if he changed his Y pipe or not.

My thoughts are on my vehicle to leave the stock one and change out behind it.
I can tell my vehicle breathes soooo much better. Hopefully a little better mileage too. I need to be much lighter on the throttle at 55.

Anyway I do notice a touch lower torque (nothing bad) at lower rpm's. It does however REALLY wake up as the rpm's build. Mine is a daily driver mostly city so I wouldn't want to risk losing too much low end by opening up too much since that's where I'm normally at.

I knew with the headers I would most likely need to do something with the O2 sensors. I'm not opposed to the simulators but I think I will try the spacers first since they are cheap and it sounds like most header guys have had this take care of their issues.

So what I am curious of is yesterday I drove about 30 miles with no CEL. This morning on my way to work on my first deceleration I got a CEL. Scanned it and came up with a P0430 (as I expected a 0420 or 0430). With the scanner plugged in I watched both #2 sensors and under acceleration and idle they run nearly identical patterns, however during deceleration I get this.



My question is this: Is my bank 2 sensor 2 not performing as it should or is there that much flow difference between the right and left DT header?

I realize they will act differently after headers and probably throw a code but my thoughts are that they would both change approx. the same.

I found torque lite outlet O2 sensor voltage data to be pretty unusable. While we're different in the fact that I got rid of my primary catalysts, I was able to get rid of P0420 and P0430 with 3 O2 sensor spacers (one drilled out, two left with the small holes) You could try it with less. There really is no need for the rear sensors but since you kept catalysts maybe you do want to know that they're working properly?

Ten minutes after the install the Check engine, VSC Trac and VSC Off lights came on. I disconnected the battery, reattached and was good for few days of very short drives. Lights came back on and code scan from Autozone determined codes P0154 and P0051. Any suggestions on what my next step should be? I just did the headers, everything else CAT wise is OEM with 55K miles.
thanks