Does a drag race only car need exhaust boxes?

My car is a street/strip deal and has been 6.25 @ 110 with the exhaust off, probably 50-60 pounds. The exhaust is 3" with mandrel bends, and dumps at the rear axle with Pypes SS Race Pro's.

The last race it ran was a street car deal so I ran it with the exhaust on. The boards were off and we weren't supposed to get a time slip. Someone screwed up and they gave us out time slips during the first round. My car ran 6.33 @ 109 on what I didn't think was a great pass. The second round it made a very good lick and I feel like it probably ran very low .20's but didn't get a slip.

A good exhaust system will slow a car very little. Having said that, my 60' is always slower with the exhaust on.