A monolithic catalytic converter is fairly free flowing, but given the age of a 1998 the converter is bound to have some build up, and the 02 sensors are going to start failing as well at some point given their age and the environment they have been in for the last 10 years.
I'd go with the suggestion of the performance cat and new 02 sensors while your at it.
IF your going to put the time and effort into trying to fool or get around the sensors and cat, why not just shoe horn a ZR1 engine in, that will give you real horsepower gains then any mods every will, plus you can still pass tailpipe inspection

 

if got a 98 5.7, cleaned the cats out as some call it and installed one spark plug non fouler per o2 sensor after the cats to fool the computer, no CEL and a more responsive truck. definatly worth the little time to perform this surgery and cats are still their to look at, just empty and welded back shut.

 

okay so to do this surgery i must weld the nut to the pipe.... were do i get the nut lol.... and im not to sure on the placement... a picture in crayons will probably help.... no joke lol just slip the non fouler in the hole and screw the o2 sensor on top of it or what????

 

That is exactly what you do

 

seriously people. lets get with the program: http://www.amazon.com/Chevrolet-Silv.../dp/B001QBU066

 

What if the catalyst converters are removed without even touching the sensors, will the sensors stiil act as if nothing was ever done to it

 

I got a 2015 Chevy 5.3 1500 I have it straight piped but want it louder does anyone know the best way or what tuner to buy cheap if possible to deal with the o2 sensors after the cats get cut out so there no engine light does anyone know if the spark plug spacer thangs work to help the lower sensor NEED HELP

 

No. The upstream sensor would operate normally but the downstream sensor wouldn’t detect any converter activity. Codes P0420/0430 would set for converter efficiency. If you don’t mind the CEL being on, it’s not a problem.

I’d recommend starting a new thread to get more attention rather than responding to one that’s more than a decade old.

There’s plenty of options for tuners you just need to type your vehicle year and engine + tuner into a search engine and go from there.

Only way to get louder exhaust will be to shorten the straight pipes.

 

Find a tuner to delete rear 02 dtc so they won't set a code, or buy an hptuner for a couple hundred, spend the $100 to be able to tune and delete what dtcs you don't want to set. You would be amazed the extra HP a LS makes with a few degrees of base timing and adjusting shift points for proper tire diameter and upping shift timings and line pressure does, worth the money for me, also takes about 10 minutes to disable afm too.