Installed Thorley Headers on my 4.0

I got mine installed yesterday. It took me about 90 minutes. Having a 2nd person to hand me tools, and help line up the headers would have been nice, but it still wasn't bad doing it by myself. No bloody knuckles or scraped arms. I used a 1/2" impact gun, 3/8" air ratchet, 3/8" ratchet, 1/4" ratchet, 10mm, 12mm, 14mm short and deep well sockets, socket extensions, wrenches. A 7/8" boxed end wrench for taking the O2 sensors loose. Oh, and a Griot's Garage terry cloth fender protector.

I had a little trouble with the nuts that hold the Y-pipe to the header, but that's probably my own fault from when I installed the URD Y-pipe. I put the nuts on with an impact gun. I probably got the nuts too tight. I ended up just breaking the headers studs.

Removing the passenger side stock header is the easiest. Going through the fender is the easiest way to get most of the bottom header nuts. Installing the new passenger side header was more difficult than the drivers side. It helped once I bent that lower support bracket out of the way, and took loose the bolt that holds the oil dipstick tube.

I re-routed that wire loomed blue wire on the passenger side by the A/C lines, cuz it sits kinda close to the new headers. I unplugged it and routed it up by the brake lines.

The new headers come with 4 bolts. These are to fasten the Y-pipe to the header. You're supposed to reuse the stock nuts, but since I goobered them up during removal I got some new nuts and bolts. I got into my bin of Stainless Steel fasteners and got some 3/8-16 x 1.5" bolts, washers, and nuts. It fastened up nicely.

The exhaust is not as loud as I thought it would be. It's still kinda loud for my taste, but I can mess with that later. I might add some Ensolite under the passenger side cab carpet, as that's where a lot of noise comes from when I really mash the pedal. Through the floorboard I can hear the exhaust flowing through the Y-pipe and 3" piping that's ahead of the muffler. Maybe I'll add a 2nd muffler. It would probably have perfect volume if I still had the stock Y-pipe or stock muffler. I have no cats at all, and none of the exhaust system is stock now. For comparison, my truck sounds about the same as a Dodge Ram with dual straight pipes out the back. Just a hair on the loud redneck side, but not unbearable.

I can feel the difference in the motor. It gets up to the higher revs faster. It shows the most difference when I'm on the highway and I mash the pedal to pass a car.

Can't wait to get my Wideband hooked up and retune my MAF calibrator.





Here's how they perform on a 4.0 FJ.

 

Nice write up man! Notice a difference? (seat dyno)

 

so is that legal now? it removes the cats no?

 

Totally illegal since I don't have the stock Y-pipe either. Which means I don't have any cats at all. If you kept the stock Y-pipe you'd probably be fine, cuz it has cats in it.

There's no vehicle inspection or smog tests in Ohio. Yay.