Pass emissions: no test pipes, HFC questionable.
Don't want to be heard 3 blocks away: no test pipes definitely, and likely no HFC. Test pipes will sound louder than HFC. The sound may be raspy with test pipes.
HP gains: get Stillen Gen3 cold air intake, HFC or test pipes, and an exhaust, then dyno tune the car for optimal gains.
Test pipes/HFCs will help free up the flow and yield HP gains, but at the cost of increasing sound levels too...you have to decide what you are willing to live with.
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2012 GT-R Black Edition Jet Black
2010 370Z 40th Anniversary // SOLD
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