Got beat by DSM

[4g63t]

So i was driving around last friday night when i see this sweet dsm come up i ask him what he has under the hood, he says stock, and i thought with my bodykit, 18's, windsheild wipers, racing seats, indiglo gauges, f&f tail lights, body graphics and paint job, springs, and struts i would be able to be beat him.
Anyways, we pull up to the crosswalk waiting for the light to change, we take off neck and neck and at the end of second he some how got ahead of me by like 5 cars. At the end of the road he was ahead of me by like 10 cars. Idk how this happened guys what do you think happened? I thought with my mods that i would have like a 200 hp increasement. I looked under his hood and sure enough it was bone stock.