Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_name_77 (valvetrain VARCHAR, fuel_system VARCHAR)

### Question ###
What Valvetrain has a fuel system made up of petrol engines?

### Accurate SQL ###

SELECT valvetrain FROM table_name_77 WHERE fuel_system = "petrol engines"