I dont know which you measured but the skyline core is 24x11x3

 

If you want the TRUST 180sx intercooler kit enjukuracing.com
is the cheapest $860 USD. your hot pipes from the OEM turbine is 2.5 and the trust I/C kit provides the cold side pipe which is 3 dia.. HeavyThrottle.com sells the Mandrel bent hard pipe for $80