60' time/brother says I weigh more is why

Guys my brother says the reason I got a better 60' than him is due to me being 40 lbs heavier. He weighs 165 and I weigh 205. I invited my brother up from N.C. and we spent a few days together and we went to ATCO, N.J. with my car. My best on the night was a 12.413@109.8 and his was a 12.420@109.7. My 60's out of three runs was all in the 1.66-1.68 range his best was a 1.70. So to answer my brothers question does the weight of a driver help or hurt a 60' time? I told him I knew the car much better and where it needed to be launched from. I told him exactly, including burnout on the ET Streets, and RPM's at launch what to do. So why did I beat his times? BTW he has a LT4 H/C in his 88 Z28 and drag races as well, so its not like he never tried it. He also reads this board,
Fred

If the car isn't spinning the tires this is a non issue. The goal is high horsepower and less weight. Sounds to me like you guys are launching at a slightly different rpm and the converter is hitting harder for one of you. That difference carries through the 1/4 mile. Also, something as simple as being a couple of inches deeper or more shallow in that stage beams can account for the difference. Way too many variables to blame the difference in performance on simply one thing.