Yes.Mandarin四[si] is differen from Englsih [si:] 。the mothed to produce[si]is: [s]is a voiceless sound.I is produced by putting the tip of the tongue toward the back of the lower teeth and letting the air squeeze out from between the blade of the tongue and the upper teeth. chinese [si]"i "here ia an unique Chinese final .it is produced by saying "s"first to form a narrow channel between the blade of the tongue and the back of the upper teeth,and letting the vocal cords vibrate. Cay you make it?

you must know the English word "sea" , it should be pronounced as [si:]. If you want to pronounce 四 with a standard pronounciation, you can try to say "sea" but remember to omit the later part of [si:] ,it means just [s]. The most important point is read [s] with the forth tone. Try it and hope it can help you!1

si4 四

Yeh Queenie they rather like ba (8) because it has the same sound of luck or so right ?

Yes, that's right!... 四 si4 ( fourth tone) And as I know, Chinese don't like this number! Because the sound of 四 is the same with "death" 死 (si3)