Diff - This looks the tits, well done mate
stevie.t - As the man says the CA18DET is older than the SR20DET. The engine code can be decoded easily, CA or SR is the block's name, 18 or 20 is the engine size (1.8 or 2.0), D means double overhead cam, E means electronic management and T is for turbo.
CA18DET is an iron block, with ali head. The cams are belt driven, the cams operate straight on to hydraulic lifters on top of the valve. 167bhp stock
SR20DET is an ali block but isn't any difference in weight. The cams are chain driven, they operate the valves via hydraulic lifters and rockers. 200bhp stock
The SR20DET can make more power. The CA get's a bad reputation for crap big ends. The SR though is now suffering from the big ends and some people are snapping the rockers. If either engine is well maintained then these big end issues don't occur.