Okay, so I ordered a long runner header, and installed it. Now it sounds extremely junky, and so hoping I can get some help troubleshooting the noise.

The flanges were offset from each other probably 1/2 inch. However, I clamped them together see if once bolted, if they would line up, and they were less than 1/16th of an inch out of flat once they were clamped, so I felt okay, figured they would flex into place.
Other than that, everything seemed to bolt up okay.
So now, when I drive, it is fairly quiet with the cruise control, but if I give it any gas, going up hills, or going over 60mph on the interstate, it is loud. Not just noticably different, but outright junky sounding. Rattley, clicky, like a smashed open, rusted out, catalytic converter.

Is there a Torque spec on tightening the bolts on the engine? I didn't use a cheater bar, because I didn't want to break a bolt. What about torque on the rest of the connections?

Should I replace the gaskets with OEM ones? Seems like I read somewhere that was the way to go on this.

Also, when I took loose the Y-pipe, the donut gasket was somewhat ugly. Not obliterated, but ugly. I went to get another one, but the one that they sold looked a little too small, so I just put this old one back in.

Also, the Y-pipe is EFFED. I got the header on, and the exhaust was still clogged, so I took the Y-pipe off. Was nearly impossible getting the O2 sensor off this pipe. I used a 2 ft cheater bar for every turn, finally get it off, and it's horribly cross-threaded. I was hoping I could clean the threads up in the pipe using the plug bolts that came with the header. forced one in a ways, ruined it as well. After cleaning out the Y-pipe and trying to put it back together, the O2 sensor wouldn't even start. Has maybe one good thread left on it. So.. Anyone know where I can get a cheap Y-pipe? I don't have re-threading tools.

In the mean time, is there any engine management issues I need to worry about (other than the check engine light) due to this O2 sensor not being installed?

So, any suggestions? I'm tempted to just take it to exhaust pro, tell them I have an exhaust leak, tell them the O2 sensor was cross threaded so to not weld up that hole, (I put one of the plugs in it that came with the header) and then see what they do. I'm driving to Columbus Saturday morning for Rock on the Range, and so am hoping to not have to listen to the junky racket the whole way up there.

Oh, and this is an '03 GS300, with 94k miles on it.

 

okay, nevermind, sort of.
I used OEM gaskets, and the copper rtv, sounds MUCH better, but I still hear a leak.
However, the O2 sensor was cross threaded, so I was unable to put it back in the Y-pipe. I just have a plug in there now, until I can rethread the Ypipe hole, and buy a new O2 sensor.
Is the O2 sensor on the Y-pipe even necessary though?