Ted is right about the addition of a 2.55 upper - the IAT2s skyrocket and the amount of timing you need to pull makes the gains negligible unless you are driving on race gas. I have attempted multiple pulley combinations and found this to be true. I am working with D3PE to try to construct a revised intercooler - but as of yet it has not happened. If anyone knows of a company building intercoolers (not HX) for a ZL1 let me know.
2012 A6 Coupe 630RWHP 10.93@125
Mods: ID850 Injectors; D3PE HX, Reservoir & Atmospheric Catch-Can; LPE 2.55 Upper & 9.1 Lower Pulleys w/ ATI Damper; LPE Idler Pulley Relocation Bracket; "Green" Serp. Belt; Cat delete;ADM Exhaust Override; Magnaflow X-Pipe Muffler (in addition to stock mufflers); Cold Air Inductions CAI; 160 thermostat; LS9 Isolator; Port/polish snout and intake runners; LPE GT9 camshaft with dual springs and titanium retainers; Kenne Bell BAP, Install and Engine Tune by Serious Hp; Fab work by D3 Performance Engineering; Trans Tune by Keith; Coming Soon: Flex Fuel Conversion.