Stage Two

In terms of describing manufacturers' motives for component selection, much of what applied to the Intake System, also applies here for the exhaust; where cost & noise-levels are given priority over bottomline performance.

On the stock OldSchool MkIII Turbo, the exhaust starts out with a somewhat tubular exhaust manifold bolted to the cylinder head of the engine. From there, the exhaust gases meet the turbine side of the turbocharger, where they meet the turbine to create that wonderful thing we know as boost. After the turbo, Toyota installed a cast iron 'elbow' as an intermediary to the exhaust system proper. On the underside of this 'turbo elbow' is attached what's known as a downpipe [DP]- which comprises the 1st bit of actual tubing the exhaust gases meet up with. Stay with me here, we're getting to the tailpipe :-)

The stock DP [at least on California Supras], includes a pre-Catalytic Converter [pre-CAT], whose primary purpose is to be the initial step in reducing hydrocarbon & carbon monoxide emissions. Since CATs are more efficient at higher temperatures [~800F+], its proximity to the engine takes advantage of the higher temps found there.

The DP is then connected to the main CAT, where the rest of emissions cleansing takes place. From here, typically recognized exhaust parts comprise the remainder: 2.5" piping, resonator for sound attenuation, more 2.5" piping, the muffler, & finally the muffler tips.

Finally, the mods!
Since the air pump analogy used in the Stage One write-up carries over to Stage Two, we'll re-use it to get the concept across to you...except, now we're looking at efficiency out of the pump.

TO BE CONTINUED.....