Simplify the following text for a Grade 7 native English-speaking person.
Original: This became dominated by rear-engined Coopers drawing on their Formula 3 and ` Bobtail ' sports car , with Porsches based on their RSK sports cars enjoying some success .
Simplified: This became dominated by rear-engined Coopers and Bobtail sports car . Porsches cars based on their RSK sports cars enjoying some success .