Thanks,
Interesting read
I have a 83 500 SEC Euro so not sure of compression.
The 380 manual said 91 octane
Last tank I got Chevron Prem
There octane ratings are 87 89 91
They have no 93
It would appear only the premium has the techron additive.
Also confusing is the units of measure
so you can't just go by number alone
My car sat a few years so I'll give it the Chevron tech & pay the addtl cost just for the peace of mind.