hi mate. tell you what i,ve have done rb26 dett. 20/50 £5 engine oil, first 300 miles, 1 bar boost made the engine labour slightly, town work, hills etc 4000 rpm max. now changing to 15/50 semi synth for the next 200 then fully synth and mapping. mine has been bored and rebuilt with new cams by myself no garages. mot was sat, 3 miles on the new motor, did 70 miles sat as above then went to elvington totb sun another 170 miles no oil used and runs like a good un.. hope this helps.. p.s will be on track at silverstone sept, so no mercy there then. bernie.