Id say your best bet is to get a TRD exhaust or a tanabe exhaust...both are great exhaust systems for the celica and with 650 ull still have money left over for another small mod, maybe save it for that InjenSRI, I have the InjenSRI and i couldnt be happer with it so you could go for that too as a first mod
The company that Easy_C is with, TPR, the ones who make that awesome Intake that is like a transformer, from SRI to CAI and has better Dynos than the Injen and AEM, they should make an Exhaust soon, after they make their Headers that I heard about earlier.
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