It is super broad but has to be computerization of everything from fuel injection to airbags and structural design. If I had to narrow it down, I would say safety (more specifically SRS devices). I think direct injection and turbocharging are also huge advances, but neither would have been possible without advanced electronic measurement and processing.

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TC
Current stable:
- 2004 Mazda RALLYWANKEL
- 2007 Saturn sky redline
- 2004 Explorer...under surgery.

Past: 135i, GTI, 300E, 300SD, 300SD, Stealth