For 2 years I 'v used Mobil 1 15W-50 in my Z car. Except for a header, it's bone stock. The car was never equipped with a catalytic converter. It consumes VERY LITTLE oil between changes and has 150K miles on the bottom end. The car has a 4-speed manual, factory a/c and I drive it HARD. As some may remember---the valvetrain on Zs of this vintage is SOLID and requires adjustment every 10-15K miles or so. The Mobile 1 has the higher levels of ZDDP that flat tappet cams like. But I'v read some good reviews here 'bout Pennzoil Platinum. 5W-50 is availible at the local NAPA. Question is: Does it contain adequate amounts/PPM of ZDDP to keep the valvetrain happy? Nightime temps RARELY drop below 40 degrees here. And right now temps are in the low to mid 90s.