400 to 416 how to? HELP!!!

[08trx400ex]

I have an 08 400ex that I discovered yesterday it only has half the compression it should. This is due to me turning it upside down in a pond on accident (dont ask) and water getting in the motor. I cleaned out the carb and stuff and rode it for about 3 hours the next day. Im guessing I did some damage that day. I thought it was my carb and after 2 rebuilds and ordering a new 450r carb, I now know why it was running rich. I am needing some advice on where to even start fixing this issue. I wish I could go back to stock but I am guessing that the sand in there has done some damage and now I am going to need to bore the motor now. I am needing advice on the best kit and price and cam and everything related to doing this so that I can someday ride this thing again. I am open to any and all comments, advice, suggestions and opinions. Please help. I will be doing this rebuild myself. I mostly trail ride with some light track riding mixed in. I do not want to get into the running hot issues or having the biggest fastest quad around. Need something reliable more than anything. Thx ahead of time

[rideracelivemx7]

you can seach 416 kit pretty much anywere and you wont have trouble finding a kit. but you cant do the whole kit yourself, you ll have ot have it sent to a machine shop to bore out the cylinder. 416 you wont have a problem with heating, i have a modded 440 and heating isnt an issue. you kit shouldnt be to much, and boring might ring you up around 150, an the 416 is the more reliable of the bunch and you wont have to worry abot doing head studs. how familiar are you with motore work