B16Riot

Ok so i purchased a B16 SIR II with a p30 ecu from a website. I installed it to a 1996 civic dx. Once it was in i gave it a couple of test drives but it seems to not have as much power as i thought it would. I have driven these cars with the same motor but mine seems a little weak in power. I was told from the website to use a Ex harness but idk if it would make a difference. I ran the b16 stock with a Mitsubishi eclipse and lost by a good amount of space. Then i ran another b16 stock from a 2000 si and i beat it by way more. I was just wondering what could keep my car from lacking power. Thanks in advanced.