Simplify the following text for a Grade 9 native English-speaking person.
Original: In 1972 , the formula was changed to increase power by permitting 2.0 L production-based enginesâ '' Cosworth BDs and BMW four-cylinder engines dominated the early years , with BMW-powered Marches gradually establishing dominance .
Simplified: 2.0 L production-based engines were allowed . Cosworth BDs and BMW four-cylinder engines dominated the early years .