intake manifold 5hp briggs and stratton

#1
Is it possible to build an intake manifold for a 5hp engine? the motor has been bored and has a bigger cam in it. it makes 12hp on the dyno and runs on alchohol. i just ordered a 25mm carburetor. it is also straight piped. what does the intake manifold do? will it increase hp? how can i make one?
 
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