Air dam for higher top speed

[Chris67SS]

I'm trying to squeeze other 15 mph top end speed out of my 67 Impala SS. The steering starts feeling a little light before the car reaches the top speed its geared for. I wanted to keep the stock(ish) look of the front so I made this air dam for the car out of 0.125" aluminum. Its mounted about 4" behind the bottom of the bumper, following the contour, and about 4" off the ground and a 10 degree forward (at the bottom) angle, painted flat black. I haven't had the opportunity to try it out yet, any input on this project would be appreciated.