My P38 Thor 4L has a full recon engine with about 50k on the clock.
I've done about 20k with 20/50 engine oil / filter changed every 6500 ish - no issues at all.
Rave mentions 10/40 Semi Synth.
Looking at changing the oil soon and just musing whether or not to go to 10/40.
I've just laid out circa £400 for tyres and will cry buckets if the 10/40 duffs things up.
What say ye ?

I used to run 10W-40 (or maybe 15W-40) but when I went to V9 Developments I they asked what oil I had been using and they said it was too thin. Now I run 10W-60 Castrol fully synth and change every 10,000 miles.

I too run 10w60 Castrol or ELF..

The RV8 was designed to run a 20w50 originally, nowt much internally changed apart from the Crank Driven Oil pump, which is far more efficient at pumping thicker oil than the Dizzy driven one of old..

10w40 is recommended for Fuel economy and emissions reasons, not necessarily for engine protection..