Ok,,,,since we are after all talking about cheating the emissions test here,,,,,If you have dual exhaust,,,,do what i have done on many occasions,,,disconnect one of the tail pipes after the muffler,,and just as it goes over the rear axle,,,,then make sure the remaining Tail pipe is very visible,,,(even put a chrome tip on it) then take it through the emissions test.
They will calibrate for 8 cylinders for example,,,and the probes,,
( the ones they stick into the tail pipe),,,,will only be reading 4 cylinders,,,,unless your car smokes like an old chimney,,,you will pass every time.