Not on my truck, but on my 2000 Camaro SS, I ran the exact same ET and MPH's with cutout open or closed. Obviously, it made more noise open, but 60 foots, 1/8th miles and everywhere else, the numbers remained constant and equal.

This wasn't a fluke, or a one time raced car...this was a 3755#, mid 11 second NA baby cammed A4 car that had a few hundred passes on it, was deadly consistent, and yanked the driver's wheel on every pass.

http://www.youtube.com/watch?v=adh4BnfBMBg