it means the higher compression version of the 1uz which was introduced in the 95 ls400 and 96 sc400, the compression is bumped to 10.4 along with other minor changes. I have driven sc400's with both and there is a noticable difference, also the idle seems abit smoother on the later engine, at idle the exhuast note seemed to have no pulsation, just sounded like a solid tone. they dyno about 20rwhp more than the 90-94 version so that's about 25hp more at the crank.