power upgrade charade


i am new to this forum and site

i realy can use some info about how to hop up a charade 1.3 16v hc engine

to explain this is a long story

but i will try to keep it short my son did use to race speedway motorcycle,s
but he change.t his mind and wanted to go racing cars

so i bought a charade 1.3 16v 90 hp ( i believe )
its dirt track racing

the rule say,s the Original engine needs to be fitted in the car end should be stock ( or look pretty much stock )
1300cc is the max for his class ( Junior racing )

so every tip is usefull becouse there is verry little info or upgrade parts in holland for a charade g200
but he wanted a charade

so is there info to find

or is this going to be a : how to get performance topic :

i hope people here can help