ok i went 14. with my ls. i had, intake headers and itr pistons. my car was also 2262lbs stock. i dont see you having a problem running mid to low 14's with a fully built ls. your never gonna get anywhere with oem pistons in there so thats a definate upgrade. as far as the intake manifold??????? i wasnt to sure about getting one because ive never seen anyone use a after market manifold on a ls and i would want to see in person how it performed. but swapping a vtec head would be better off