turbos dont add hp, turbos add denser air into the combustion chamber which in turn makes ur engine able to burn more gas which makes for more my, turbos typically can be built for different boost pressures, normal atmospheric pressure is 14.4 lbs a sq inch at sea level, so if u put 7 lbs of boost on ur engine ur gonna gain about 50% power theoretically, now u will normally only see close to that 50 percent if u have an intercooler to cool down the air flow, so adding 14.4 lbs of boost pressure would gain u 100% of ur engines original hp if there werent the other factors that rob u of that hp, which im not gonna get into because im lazy and tired, but if u start with a 200 hp engine a with a turbo u can easily make an extra 100 with a 400 hp engine u can easily make an extra 150-200, without ever pushing serious boost pressures. but if u only start off with a 100 hp platform yes it will be very hard to get out 100 hp without serious boost pressures how that makes sense to u.