I put a hi-flow cat on my 95 ls and I really couldn't tell much of a difference in sound. I did seem to lose a little power though. I guess I lost a little backpressure or something. Be careful if you are just going to go straight pipe all the way back because my might end up losing power. But since the gs-r has more horsepower you might be ok. and if you want loud get the apexi n1. that is loud.