My spirit rt on a stock cpu and stock turbo with +40's and afpr. I spiked mine to 18 and it fell to 14 before cut out. I ran a 04 cobra with intake and exhaust, we were dead even. Both of us was on nitto dr's, guy told me he did the 1/4 in the high 12's.
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But thats about all the stock turbo will do.