regarding full synthetic oil

72bluNblu said
If the chemical makeup of Castrol GTX had stayed the same for the last 50 years you’d have a point. It hasn’t.

Pretty much all the major oil brands have dropped the zinc content of their non-specialty oils in the last decade (or two) as most cars run roller cams. The Castrol you buy off the shelf today is not the same oil it was 50 years ago, that’s a fact.

For the most part, only specialty oils still have appropriate zinc levels for a flat tappet cam.

Now whether the OP has a flat tappet cam or not, well who knows.

Understood, and I realize this is a fact.
Just saying I have personally never had cam/lifter or any other lubrication failure using either of the two mentioned oils with flat tappet valve trains.
I do think it’s possible zinc additives may be more important with todays lack of metal and machining quality.

RustyRatRod said
I have always considered 20/50 a VERY heavy oil for our engines. That said, I've seen a LOT of people run it through the years and every time without fail they had great service from it. I tried it in my slant 6 and it literally made it feel like it was bogging down trying to start cold. It would start and cut off several times. I could also tell a difference in how the engine ran. It would not idle well until it got warm. I ended up switching it to the same I run in everything now. Motorcraft 5/w20 synthetic blend and zinc additive added to it. As soon as I made that change, I felt an instant difference in how the engine ran. I couldn't believe it, but that's what happened.

Not sure how to address this.
Maybe your motor doesn’t produce enough power to overpower the oil pump?

Gotcha :D

Seriously though, I have never experienced anything like that.
Of course every single time oil comes up there is always other opinions.
The OP is in Florida where it can get pretty warm, and 440’s are not generally regarded as high winding motors with tight tolerances.
Those two facts are what guided my suggestion.

Sure, if it was a motor originally designed to run synthetic my recommendation would have been different.