Nissan never turbocharged the EFI CA20E or carb CA20-S, any CA20ET or CA20DET you have had has been put together by someone else. The only CA series engines with turbos made by Nissan are the CA18ET and CA18DET.
There is no shut down procedure for normal UK driving. My 200SX owners manual says "let it idle a few minutes before shutdown if the vehicle has been driven at high speed continuously" IE Don't come screaming into the pits at a track day or do a long Autobahn run at
100+ and just switch off in the service area. Normal 90ish UK M-way isn't really high speed. Start up is more important, let engine idle for 30 seconds when cold before moving off slowly at first - allows oil to circulate and thin a bit so it's actually getting to the bearings and not just spewing out the pressure relief valve. Don't use high revs from cold or immediately after starting - again lack of oil flow. Change the oil when we say not sometime when you feel like it!