probably by draining oil and coolant----

those were some of the worst smog years with restricted everything, low compression(if any) when they were doing everything possible to for emissions before the cat exhaust came out

I don't remember the exact number, but as an example, Ford s 460 powered cars went from like 70 some emission items to around 12---check valves, solenoids,vacume this,that, timing retards , egr, air pump

If you want performance---you will need parts near the specs of the late 60 early 70 (pre smog) era

TA or W2 type stuff, good headers/exhaust,intake/carb