well make that x4. i dont care what so-called engine builders, tuners whatever say.from a metal mans own mouth 160 -170 is what metal prefers to do its work in.now ive run big blocks small blocks and almost no blocks lol and ive noticed that any car we have had seems to do its best when its 160-170.trans included. the cooler the trans =less friction.according to a guy whos built racing trans for 50 yrs.back in the mid 80s i had a 55 that i could not get to run consistant at all. my buddy who built engines for many more yrs than i told me to write down my temps at the launch and at the end on my timeslips.do that for a few weeks and bring them to him. he went over them and showed me that when my car launched at 150-170 i had alot better times.when it was runnin any hotter i realy dropped. sooooo. we made sure that little old car stayed cool.