i ve taken out a part of catalystic converter after it broke inside its housing due to an impact.but as my car is driven on cng, it didnt show any change.n CAT was very clean and not choked at all.
now,if u take it out,there are a two problems.
1) exhaust will be a bit noisy, not much though.
2) fuel economy will drop if u put the sensor of CAT in an empty housing.
some expert member testing his new civic with and without CAT and he reported drastic increase in fuel consumption.
So basically, the ONLY way to get ur car to where it was before is to spend some heavy cash and get a new CAT, and to protect it from being choked again, mix hi octane with regular fuel.
Btw, i have an idea which MIGHT work.i ve not discussed it with anyone yet nor tried on any car.its just a plan.
what if u drill a hole around 1inch wide through the CAT? this way, exhaust gases would be partly filtered and they ll also have more free flow effect so it might not be very bad on fuel economy.but u ll have to check if this car work or not.