ok here goes, there is no point of spending loads on exhaust work and leaving the standard muffler on. u increase the flow mid way and u choke it at the end. the result possibly no change or decrease in performance. what you can do is invest in a good muffler and exhaust system. u will not get the annoying exhaust sound, what you will get is a deep bass sound, probably pretty quiet on idle. higher flowing exhaust muffler with great sound aint gonna be cheap but certainly worth it. About ecu tuning and all.. most times is not about how much Hp but the power and torque curve. a well tuned machine has good power delivery. you will be surprised how a lower hp car but good power curve can do with a high hp car with power curves high up on the rev range. A street car needs good midrange as your not on the straights all the time.