ET advantage

Could any one tell me a formula for converting weight into ET? I know 100# is approximately a 10 tenth in the quarter, but what about the 1/8 th mile? My car is 3200# and the average competitor is approx 2700#. What is that 500# worth in the 1/8.
Also trying to guess what ET difference my car would have on front overhang. I know my car has 36” on an allowable 45” overhang. Would that 9 “add maybe a 100th? Just trying to justify the changes on my hooptie to be more competitive or just buy another chassis. My car runs 4.50s now at 3200#, I wonder if a 300 to 500# weight drop and front overhang extension would get me in the 4.20 range. Thanks for all help howard.

 

I think 9" @ 160mph(guesing your about there) will be about 3 thou.