How to use pivot in sql server

hi I want u use pivot in my query when I don't know the value of attribute

table script is

create table Demo ( id int identity(1,1) primary key, car_id int, attribute varchar(max), value varchar(max) )

 and my select query is----

select car_id,[Engine Type],Width
from Demo c
pivot (
 min(value)
 for attribute in ([Engine Type],[Width])
) pvt

when i don't know the value of attribute than how to implement select query, please help me