If you are doing a custom exhaust, keep in mind that your celica is n/a (naturally asperated) or NON turbo there for you need to have some back pressure for optimum hp
. If you remove your cat and resonater your exhaust will be nice and loud while your car is going nice and slow. Your best bet is to put in a new exhaust with wider piping from the resonator back. I have the best sound around and not another celica around here can even touch me. 15.6 @ 89mph
with no engine mods, just exhaust and butterfly valve removed!!