BMW Repair Questions? Ask a Mechanic for Answers ASAP
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The only engine I would sensibily put in your BMW 318i vehicle is another 1.8 BMW engine (i.e. a like for like replacement).
No doubt there are places that would tell you you can put some higher powered engine / gearbox into the vehicle however you are then getting yourself into the realms of Electrical / Electronic control systems in your vehicle not being compatible with your new Powertrain!