Yes, with 91 percentile you can get ECE and CS in some of the NITs. Some of the examples are:

• NIT Silchar - Electronics and Communication Engineering
• NIT Srinagar - Computer Science and Engineering
• NIT Andhra Pradesh - Electronics and Communication Engineering
• NIT Meghalaya - Electronics and Communication Engineering
• NIT Hamirpur - Electronics and Communication Engineering

To have a list of all the institutes which you can get based upon your rank, you can use the following link:

You can use the following link to predict your score :

https://engineering.careers360.com/articles/jee-main-marks-vs-percentile

Good Luck!

Hello Student
Yes Definitely you can get a good institute and also the system of allotting marks have been replaced by allotting percentile ,and cut offs are different every year, but i dont think it will go beyond 65% for an SC student and scoring least above 90% (actually much more).
Thank You