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Ford 2.0 liter ZETEC. It's versatile. Used in Formula Ford race cars and Sprint cars and everyday drivers. Very durable motor.

What about the old Dodge 2.2 ltr n/a and turbo motors. Bulletproof and can make serious power. Used in everything from minivans to Formula Dodges.

Can't forget the aircooled VW/Porsche flat 4 boxer engine. Probably the best of all time.