well the nsx has a scoop intake that mounts on the back and under high speed is said to actually create boost. now in doing this your map would freak considering its seeing this "boost" anyway i am sure it could be possible if you got high enough speeds but the normal "track" conditions of driving i dont see that happening. make sure you take pics if you do this...

 

the 1100zx ninja gains 20hp from its ram air at high speeds

 

correction, the zx10r

 

I think AusS2000 is right. The amount of positive pressure you'd likely achieve could probably be gotten using a NACA duct. No way is this "ram air" going to be "boost" which implies something around 5+ PSI.