when you go to see a car there are some basics that have to be done in terms of checking engine. there are some things you can do before you start looking around. look for engine that have no mods at all, so there less chance it has been abused. look for cars running standard boost and standard turbo setup. take a compression tester with you and a spark removal tool (if possible) make sure the engine is cold when you get there. you want to here an engine on cold start and the warm up for any strange noises ( if possible) check condition of oil, and general maintenance by the owner. does the owner have the know how and money to look after the car?? why are they selling it? take the cam cover off and look at the colour of the oil and condition of the cams. will show you oil condition and any oil starvation. try to find a engine that has original parts, example original head gasket, sump sealant and injectors and so on. also look at the bolts on the engine for marks make sure they have not been undone at any point. even after all the checks in the world some engines will still go wrong, its just on of those things. i hope its a good one mate