How can your car weigh less than a polo ? It's impossible unless all you have is a chassis and a engine, what everyone is trying to do is make u see sence because that engine won't pull skin off rice pudding, any mods you do to it will probably get you back up to standard horse power especially as it's in a heavy car so will be under more strain, easiest mods would be a panel filter and airbox mod and a cat back system but like everyone has said it's a waste of money to modify said engine.
Sorry for poor punctuation but I can't be bothered lol