Spark Plug for 4AGE BT 20v engine is IK20.
For further information, u may refer this website
http://www.globaldenso.com/en/products/aftermarket/plug/basic_knowledge/heatrange/index.html
I m going to sell my gtr 34, this car is full modified from HKS (Japan) come with original 699 hp, blue body colour with 18' TE37 , and all HKS stuff, twin big turbin. selling 3xx k (with ngo) . any one interested...