hi sae3dkhan where are you?
im in nottingham welcome to the site as for what engine you want well thats all down to you your budget and your skills, if you like to tinker and want a cheapy you can get a happy time kit with all you need off ebay for around 120 bar but personally ill be getting a four stroke honda clone and chain drive i think but ive also been considering an electric system with an engine for power rather than a battery set up but im unsure wether its workable