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So the verdict is that I shall use Caster R or Castrol Classic 20-50 on my newbuilt 1293 S-engine for historic racing??

No mention of Valvoline, so I thought I'd stick my penniesworth in.
Used said oil for many years in my rally engines and never had any serious issues.
With a new motor I used the standard oil for running in, drain the sump then refill with the racing oil.
At the moment I'm using Morris's classic 20/50 oil in my road car. No issues whatsoever.

Remember that racing oil is different from road oils. Different additives / detergents etc.
I don't think racing oils are happy in an engine for extended periods of time.
-Re-built a road engine recently for a friend, who always used racing oil in his classic(not used extensively, oil changed every year). There was over 1/4" of sludge in the bottom of the sump. The lower layers of which had actually gone quite hard

Sounds like classic castor waxing to me.

Oddly enough, you need to get the engine hot to boil off the moisture. If you run castor in a rarely used, unthrashed engine, the chances are, it'll wax up. Oilways and all. Try putting some of the gunge on litmus paper.

He was using mineral oil, not Castor. He never drove the car hard, but did drive it long enough to get up to temperature.

Actually there is some "spare" litmus paper at work.....
But where can you buy it if you don't have access to any?

Valvoline 20/50 without a doubt, holds the best pressure and seems to do the job regarding wear. Only thing is, it's no use in a car used for commuting cos its awful for gunging up the rocker cover! Imo great stuff

Use the Statoil 25W50 racing oil. Perfect for race engines with lots of ZDDP. Easy to get hold of in Norway and not that bloody expensive.

http://www.statoil.no/file_archive/bros ... jemi_2.pdf