The Celica turned twenty-five years old in 2018. That made it exempt from future emissions tests after the 2018 test, which it passed easily, as usual. That gave me the opportunity to build a custom exhaust system. I did use a catalytic converter, and it would still easily pass emissions. But with improved flow, lighter weight, and better sound.
I started with a 4-into-2-into-1 "tri-Y" non-sequential stainless steel header made for a Corolla.
These two pieces saved fifteen pounds and they look a little bit better too.
I got the header and downpipe ceramic coated. This keeps the engine compartment much cooler and it keeps the exhaust hotter, reducing back pressure and improving catalyst performance.
I decided to go with 2-1/4" tubing and a 2-1/4" catalytic converter, resonator, and muffler.
I selected a Magnaflow stainless catalytic converter with a built-in resonated core for further weight savings.
I also selected a Magnaflow oval muffler.
I installed the downstream oxygen sensor after the catalytic converter where it belongs.
Along with the exhaust system I advanced the ignition timing from the stock 10 degrees up to 15 degrees BTDC.