alchohol

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?

I am trying to sell a awesome Briggs 5 hp with a bugle exhaust. It runs off of alchohol and has a custom airfilter and carburetor also. I will also include a horstman clutch. This engine can top out at around 70 mph on the go kart pictured. I am asking 500 obo..Looking for a clone engine and...