1jz is 2.5 twin 1g is 2.0 twin the 1j has 280 hp the 1g has 210 they both use ct12 turbos but one is ct12a i think it was the 1j but basically the same turbo setup but different internals the 1g is hard to find parts for in the us the 1j not so hard. both are rare but the 1g is hardly ever seen. thats why i like mine so much. but i would still like to have a 1j myself the 1j can be built like crazy i have only heard of 1 1g being really built it was in japan it had around 400-500hp dont know what they had done.