you'll be surprize how much the stock ones can do. But if you don't have the $$ to buy high quality headers,and want a good gain in HP n20 the way to go. I have Bassani headers and for the $$ I regret getting them. If I could do it over again n20 and gears. These motors need to breath they you should get an intake spacer(Roy) instead, it gives you about the same gain as headers and way cheaper too.

 

Actually thats not entirely correct. The stock flow well since they are port matched (same as in cobra) but even on a stock mach1 LTs make considerably more power than with just bolt ons, the headers aren't expensive but they're just a PITA to install but if you can fork out the money then its definately a nice mod to have. A bolt on mach will make very low 300s at the wheels at best, there's dynos that read higher but its just bs. An intake spacer will not give the same mods as LTs, spacers are all low end torque and minimal top end power. I saw a nice improvement in low end power with the spacer and was worth the $100 but headers give a small low end improvement + a noticeable gain in the top end, typically 15-20whp, which is why guys with headers dyno 325-330whp with bolt ons. If you're going N/A, LTs are a must, otherwise they can wait but eventually you'll have to get them.