Below is an context that describes a sql query, paired with an question that provides further information. Write an answer that appropriately completes the request.  # noqa: E501
### Context:
CREATE TABLE table_name_77 (valvetrain VARCHAR, fuel_system VARCHAR)
### Question:
What Valvetrain has a fuel system made up of petrol engines?
### Answer:
SELECT valvetrain FROM table_name_77 WHERE fuel_system = "petrol engines"