your 3 best options are. 1.swap the motor for a b20 from a cr-v(drops right in) it will need to be sleeved to reach the 400hp mark but will be easer to achieve due to the higher displacement. 2.swap for the prelude h22(there's a company that makes a swap kit for the 3rd gen integra) the high output version is already at 200hp but it will also have to be sleeved for best results. 3.if you are intent on keeping the b18 that you have your best bet is to get a b16 head v-tec or non v-tec depending on what you want(for turbo the non-vtec is easier to tune) upgrading your valve train to titanium to get a better redline... all are good ideas and with proper tuning and turbo sizing 400hp is obtainable... but why 400 on a front wheel drive car you will have horrible torque steer?