According, to 2017 data you should score more then 200 marks in JEE Main to get Mechanical or EEE branch in top NITs under general category other state quota.

JEE Advanced maximum are not defined :

Maximum Marks vary every year like below:

2017- 366

2016- 372

2015 - 504

2014 - 360

 So, it is difficult to predict marks as exam pattern and marks change every year but you should score more than 50% marks to get good branch in Top IITs.

Good luck!!