B18C5-EG

Yeah i just got a JDM ITR Swapped into my EG Hatch it came with a Spoon 4-2-1 Header and stock intake tubing (no box just tube from TB to box). I still have full interior. No carpet, floorboard tar, or spare tire. It's a 95 CX so the exhaust piping is prolly around 1 1/4" inces i wanna say? The guy who did the swap hooked up the stock piping to the Spoon header and im pretty shure the stock ITR piping is like 2 1/4? Anyways it goes 4-2 part of header to a bolt on 2 part then he has a collector thing that is 2 1/4'' / 9''L Flanged to the stock piping so the stock piping runs all the way from the stock muffler to around where the firewall is. I know i need exhaust please dont flame me flame the guy who did the swap i just graduated from high school and have to pay for my own insurance, cell phone, food, and gas (having to use 93 oct now w/ the new engine NOT CHEATP!) But i raced a G35 from a stop light im on the new Falken Azenis (615) with about 400 miles on them (Like new) I had a 180pnd passanger with me at the time . Well we went and i dint realy dump the clutch (stock clutch) minor spinning caught traction shifted at 9k hit second spun little not to bad with the new tires (he spun second pretty loud) went into third missed third but he was pulling on me anyways and needles to say he beat me i guess you could say . I know the G35 runs like a 14.2 and i had talked to a guy from Skunk2 before i got the swap and he told me w/ i/h/e i should run 13 flats/low 13's so would my current exhaust setup realy hold me back that much to lose to a G35 and possably run a 14.5 or higher? Also should i go with 2 1/4 or 2 1/2 i was thinking 2/14 would be perfect but your input would be great . Thanks for you help in advance