my builder told me to use penzoil 25-50. so I did it and they ran well !

Valvoline straight 40 wt racing oil all I have ever used. My engines are always perfect at refresh PERIOD.....

Might want to look at the bravo shops neo oil, I've heard there oil is awesome, my next oil Change will be done with it, there drive oil is also producing great results!

i used the neo products often and they were superior in all respects to everything else. the problem was getting them ... almost as good were the mobil 1 synthetics which i could buy anywhere easily. their delvac product line is teriffic and what i run now in everything but if i had access to the neo's i would still use them. they are quite amazing.

My 2 cents! I have reading these oil posts for many years, what I have gleaned is multi grades gives pressure a tad quicker and has good cling due to the polymers. Dino is better for break in syn is to slick, being so slick rollers can stick and develop flat spots also it takes longer for rings to seat. On my builds I do run straight dino for the first 5 then 10 then 25 hour changes, then I switch to 20-50 at 75 hours I go over to syn. I have been running Spectro 20-50 since, but the Merc syn has been doing fine for many.

I live in TX, hot weather, and hot water, often wondered how muck that impact oil,
Not sure where you live But that may need to be brought into factor.