definitely zinc or at least a zddp additive.
Z-max works okay, but most of the motor oils that don't meet the API standards do so because they contain zinc.
zinc will coat your catalytic converters internals making it less or totally not efficient.
the imperial ain't got that problem, so the zinc is a very good idea for it.
Neither the rat rod or the 57 Olds have catalytic converters so I need to find some oil with zinc in it or ZDDP additive. I'm glad I asked Ian before I completed the oil change.
The little monster doesn't get driven hard. The car is so light it chirps the tires when the Torque Flite hits second gear under firm acceleration. Rides like a lumber wagon with ladder bar rear suspension but handles like a go-kart. Mustang II front end with 650 lb. coil springs to handle the weight of the 413 up front.
Okay sometimes it gets pushed a little. We regularly drive a curvy hilly small State Highway here in the Driftless zone. I know it well. We were placidly trundling down it one Fall afternoon maintaining the speed limit, and there are almost zero passing zones in the ten miles between stop signs the last stretch before it ends at the Mississippi River and a larger State Highway. We were enjoying that last 10 mile stretch dropping down hill in the river valley on relatively smooth new blacktop when a pair of BMW motorcycles zoomed up on our ass. These guys were sure trying for "the look". ATGATT, mirrored face shields, squared off aluminum panniers. They hovered about a half a normal car length off my tail pipes and the guy on the center line kept stretching his neck to see if they could pass. Half the population of NE Iowa drives up this road going the other way to buy apples, look at leaves, and generally get in the local's way. Oncoming traffic was an issue and the "insect" looking space aliens couldn't pass and were getting annoying with their herky jerky movements in my rear view mirrors. So I sped up, they stayed on our ass. I told Sue, "Well hang on, let's see if they know how to ride." Five miles later when we arrived at the T intersection with the bigger highway, I could not see them in the mirrors anymore. We waited maybe 30 seconds and there they came. We turned North and trundled off at the speed limit. They absolutely could not match the cornering ability of the rod. I wish the old mechanic that hand built that car could have seen that. No detectable over steer or under steer, just a flat glued to the road feel. No tire howling like a squad car just a bit squealing scrubbing on some of the less well banked curves. Sue was grinnin' like a teenage girl.
I think I need to find some zincified oil or some additive today.
