Originally Posted by R3_nyc
Do I really need too? Lol money is sort of a problem
If your new system has removed the cat, which is the biggest restriction in the OEM exhaust, your engine is going to run lean, which is harmful to it, and it's going to backfire in the exhaust, which will get you lots of unfavorable police attention.
Installing the block-off plate is essential to stop the backfiring in the exhaust which will otherwise sooner or later attract a police officer, but given the removal of the cat, that still might not completely stop the backfiring.
As for the lean condition, you need to either have the ECU tuned or install a Power Commander with an appropriate tune. Determining an "appropriate" tune though is tough given the way you created your new "system". A dyno tune would be far better. ALL of the methods of correcting the air fuel ratio now are going to be pretty costly. This is something you should have planned for BEFORE you chopped up your system in this irreversible way.
If all you want is a louder, or simply a different, sound, there are plenty of "slip-on" systems that leave the cat alone, and so don't require a tune. But, now that you have cut the OEM system, without having the funds to complete the tuning process, your choices are not good.
One way you could go is to buy another R3 owner's OEM system, which would be cheap (almost free) because no one wants the OEM system, and plenty of guys have gone with full exhausts. Then, buy a slip-on system that leaves the cat alone while still giving you a louder or different sound. However, a decent slip-on system is not going to be much cheaper than an ECU tune.
Finally, you could buy someone's OEM system and leave the exhaust UNmodified at all. THIS will be your only "cheap" solution.
You asked, so I have given you what I see as your true options at this late point.