Diploma

If you wish to do a diploma, do it after 12th, as in between diploma will not add value to your resume in future.

Hello Rahul,
I think you cannot apply for BITS Pilani as the admission is for those who completed or going to complete 10+2 system . as diploma students don't have this, they will not satisfy the eligibility conditions. So, they cannot apply for BITSAT.

If you have a great passion about car designing then you do Bachelor in Transportation Designing from colleges like:
MIT Institute of Design
DYPDC School of Design, Ajeenkya DY Patil University

You can refer the below link for college comparison:
https://www.shiksha.com/resources/college-comparison-255415-73603

Hello Areeb Shaiikh,
To know more about the eligibility criteria, click on the link given below:
https://www.shiksha.com/b-tech/course/b-tech-in-petroleum-engineering-and-technology-alagappa-college-of-technology-anna-university-guindy-chennai-167425?city=64&locality=491&fro=serp&pn=1&tn=1&ct=course&

Hello Saurabh,
After diploma, you can bid for lateral admissions in 2nd year degree course in Aeronautical Engineering in your state. Alternatively taking diploma as equivalent to 12th you can seek admission to any degree course of Engineering.