What visa the best fits my situation? is the touristic one good for me?

next fall i'm going to collaborate for 89 days on a research project in a federal institute. considering that i'm going to spend only 89 days (and the ESTA is ok for 90 days) i won't need any other visa (the professor from the federal institute told me to go for 89 days so that he doesn't have to go through the hassle of filling in all the papers to get me a J-1 visa). the problem is that i'd like to spend more time there cuz i want to get there and get used to the time zone (i'm italian) and find a place to stay..and after i'm done with the project i'd like to travel around the states for like 2-3 weeks, go visit some friends and all..so the ESTA wouldnt be enough!! so i was thinking about getting a touristic visa (B-2) that lasts up to 6 months but...can i? what happens if they find out that i got a touristic visa but i am not going to be ONLY a tourist but i ll be working (and with working i mean working on a project..not working as in paid..i wont get any money from anyone to work on the project) in a federal institute? also cuz i'm sure that, considering i'm going to a federal institute, they'll get any info about me and all so they'll know all my 'moves'..what do u think?