7 is the series; 45 the engine size (4.5ltr); the 'i' stands for 'injected' or 'injection' and the L (if applicable) indicates Long wheelsbase (extra 4" in rear doors). Parts are easy although some are expensive compared with domestic products. OEM is very high quality though.

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Good - Fast - Cheap: Pick any two.
Current:
E23 735i; E30 318i; E32 735iL; E38 735iL; R50 Cooper; R55 Cooper Clubman.
Previous:
E21 318i; E32 735iL; E34 535i; E38 730iL; E53 4.4i