Siddhartha, 

Mode of admission to BITS is

One needs to take the BITSAT examination and fulfill the BITS Admissions eligibility criteria.

Admissions are done on the basis of score in BITSAT through BITS Counselling.

So as you can see you can't get admission if you don't have a good bitsat score. 

But topper of every board get direct entry to BITS.

You can get various colleges based on your jee mains score . Check it on career360 college predictor link given below 

https://engineering.careers360.com/jee-main-college-predictor?utm_source=google-search&utm_medium=paid&utm_campaign=jeemain-clgpd

Hi Siddhartha,

To get admission in BIT, you need to appear for BITSAT and clear the exam.

It is the mandatory exam for getting admission at Birla Institute Of Technology.

BIT is a deemed to be university, and is ranked at 25th Number in the list of engineering colleges. 

for more information visit Birla Institute of Technology and Science, Pilani - courses, fee, cut off, ranking, admission & placement - Careers360.com

Hi there!!! Jee score is referred in josaa counselling for admission in government colleges, whereas BITS being a private college its counselling is different and independent to that of josaa counselling. So you have to give entrance exam i.e BITSAT to get admission in BITS. Here are the cutoffs of BITSAT: https://www.bitsadmission.com/cutoffscores2018.aspx

Hope this helps.