Just spotted the OP has a 1.1 Peugeot 106 and maybe this is the reason for the possible engine upgrade. When you say "stock car" is this as the racing field or the fact the car is "stock" meaning nothing has been done to it modification wise? If this is the case then save your money my friend. Any power gains from the 1.1 to the 1.2 will be negligible and not worth the time and effort of the engine swap. Use the car for what it is and look to a slightly more powerful model with a better chance of a performance upgrade.