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The 390 is a bit low. I expect anywhere from 406 to 420 on a stock E55. Weight from chrome is nothing. The IATs are HUGE. Especially if the car sat before or if the dyno shop didn't have nice ventilation.
RennTech Headers, huh? GGGGrrrrr!!
LOL.
I couldn't pass up the deal I got on the headers. TB is at its heels.