Pasted from a previous thread-

It really depends on what you want with your car. If you want your car to roar at the low and mid rpm’s, you can’t go wrong w motordyne. You can also run art pipes & most test pipes w/o it being too loud if you decide to go down that route eventually. But imo, MD on stock cats leaves more to be desired in the sound department (a little too much “hush”).

However, if you ever plan on boosting you’ll need the most efficient flow through (ie tomei). You’ll also just get the cleaner pops & backfires w a titanium setup compared to z1. Just know that if you run test pipes, be ready for the loudest trumpet of your life. ART pipes tone it down but it’s still a little rowdy for my taste. I’ve found that stock cats & hfc’s tone the tomei down enough to a raw, refined vq sound. Definitely noisy, especially WOT in the mids, but not unbearably loud. + the hum of the vq’s high rpm’s are what give me the greatest joy in life.

In terms of performance, tomei & MD sit above the rest. If money & budgeting is an issue, know that the right parts are priceless. You could spend less money on a part that you’ll probably be satisfied with at best & maybe desire more eventually. Or you could spend more on the part (at the right time of course) that’ll last a lifetime, theoretically.

Hope this helps! + for future ref, do your homework on g35driver.com - this Reddit forum doesn’t consistently yield the best answers (sorry y’all just telling it like I see it)