If you're worried about spending too much, why not try test pipe? Yes, it'll be louder but it's less than half the cost of HFC. Plus, TP has a better gain than HFC.
Adding HFC to your Invidia will probably add around 4~7 hp. Not significant but nevertheless it'll increase power and sound. All in all, I'm betting 305 WHP with your exhaust set up. You can try tuning it after which can get you a bit more power.
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