Which Octane Fuel for 2.1DJ - Newbie asking

[Piratepete]

Hi Guys
1990 T25 Holdsworth Villa3, 2.1DJ engine . Done 130K miles. Runs well.

The fuel cap says use Unleaded Premium 98 octane petrol. Previous owner used standard 95 octane with no issues (quote). The original VW Owners Manual also says use Premium but Standard is ok in exceptional circumstances and don't run the engine too hard.

My Haynes manual suggests either but the ignition timing should be set differently depending on the fuel. No idea what it's currently set up for.
So, all you DJ owners. What fuel do you use, is the timing adjusted for it? Has anyone experimented to see if there is any difference in performance or economy? Is premium better for the engine? I believe it has better anti-knock qualities.

Interesting replies expected!

Cheers!
Pete

[itchyfeet]

I use 95 but you should change timing to 5 degrees btdc. Standard its 98 RON with 10 degrees btdc.

[Mocki]

If you are going to run normal unleaded, the timing needs to be 5°
Timing set as standard (10°) then you should be running super unleaded .

I run mine on super , but I only use about 60l a year as a emergency because I use lpg full time