Tri Y is also known as the 4-2-1. 4 combine to 2, and 2 combine to 1.
If you have a honda D series engine fro 88 on up, the 2 part 4-2-1 96-00 civic EX (d16y8) OEM header is widely available on craig's list for 15-20 bucks and it will fit. I put one on my hatch with a 99-00 civic si cat back and a new 2.5" cat. It took 35$ worth of help from a muffler shop to get it shortened a bit and I installed it myself. The car produced noticeably more torque and quite a bit more power in that last 1500-2000 rpm before redline. I might have picked up 1 mpg or so. I have the welded assembly type oem header, there are also cast iron ones that weigh quite a bit more. Many 99-00 civics have the cat right on the head built into the exhaust manifold. If you replace that type of set up you need to move the o2 sensors back down the exhaust and this requires either buying Honda extending harness(s) or soldering your own extensions.