2 barrel to 4 barrel

On a stock 318 ( it does have dual exhaust). Roughly how much power/ torque difference would going to a 4 barrel make? I'm asking because I was asked this same question and I said probably 15 horsepower, the person who I was talking to said that it was more like 50 horsepower and I don't believe that.
Depends on whether or not you make any other changes. If you leave the 2v camshaft in the engine, it's going to make a little more power, but not a lot. If you go to a cam that's matched to the carb & intake you put on, then you'll see a decent difference. Basically if you leave the 2v cam in the engine, you're wasing your money on the new carb & intake.