Your words: "I'm only using it as a track car." Vehicles that are "not" used on public roads and highways can have a variety of modifications to enhance performance that are not street legal. The list is never-ending.
Your specific issue is by using your vehicle "on the track", you are overloading the catalytic converter with fuel, causing it to overheat and make sulfur oxides (SO2 and SO3) giving you the rotten egg smell. What I'm going to say below and doing it to a vehicle driven on public roads "Is Illegal" -- everywhere!
What you are going to do is either completely remove the cat or hollow it out and leave the shell. Remove the before and after the cat O2 sensors for either procedure so you do not damage them. Do not remove the install holes for the O2 sensors both before and after the cat because the sensors are going back in them. Once you have done that, get spark plug spacers. These are designed for engines that use oil and reduces the chance of a spark plug being oil fouled making the engine run better longer.
These spacers will be used for the 'after the cat' O2 sensor and basically fooling the computer thinking it still has an efficient cat thereby not setting a code. Do not do modifications to any other O2 sensors as it will definitely cause performance issues. The after the cat O2 sensor only checks cat efficiency and is not used for fuel metering.
Check this YouTube video about it:
Happy Racing. Glenn
Edit add on: I stopped doing Smog Checks about 2008 and the above procedure was common (though never admitted to). "If" the EPA has made issues with modifications now on track vehicles, use your own judgement. But, I've never seen or heard of an inspector at any track. Safety inspector -- yes. EPA inspector -- no.
Tuesday, March 23rd, 2021 AT 12:37 PM