Manish as I have gone through your comments and if you are getting 140-150 marks in the JEE Advanced 2018 exam under the OBC category then according to last year marks vs rank distribution you can expect around 2000 rank under the OBC category which is expected to be about better this time as due to increase in the difficulty of paper and zero error in question paper the cut-off is expected to fall down so you can surely expect atleast in top 2000 rank under OBC category.

If you get the rank in the range stated above then you can surely get admission in one of the new IITs and maybe if the luck favours then in one of the non-conventional branches of one of the old IITs.

Feel free to ask if you have any more queries. All the best!!