you can run the same ecus on a c5 as u can run threw a c3-6, those ecus are the same basically the only major mods if between the c4 and c5, the c4 having alittle bit more advanced igition up top, and less down low, where as the c5 has more igiton down low, less up top, the reason i know this is, cause well, i have 100 different STOCK igition maps, for crome, i run stock map which u can get off pgmfi.org called 253, which is b18c4 stock igiton, i run it with minor mod and couldn't be more happy, i would suggest hmotorsonline.com if u want to try and get some more info or passwordjdm.com, other then that ebay is ur best bet.. gl with ur swap..