None are cost effective.
I'd recomend....none. Exhausts make them louder, but not always faster. Intakes (K&N) make a TINY difference. ECUs rarely help any NA car. Thjey are great with turbos. I have heard that if you carefully do the proper sport exhaust, proper headers, proper ECU flash and proper intake (but careful - you can damage the hot wire/MAF), you can get 20+ HP out of it. And fantastic sound.
I did zilch. And I dont want fantastic sound, since it attracts too much unwanted attention.
Grant
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