Downforce vs Drag vs Drip Rails
 

I am thinking about cutting off the drip rails on the roof above the doors of my 1979 RX-7 GTU road racer. I suspect that they cause higher drag than having no drip rails. Do they contribute to downforce by keeping the air on the roof from spilling off the sides?

How much downforce (pounds) does it contribute?
How many pounds drag does it cause?

They probably do create some drag(thats why newer cars don't have them) But the reason they are there is that is where the stamped roof panel gets joined to the stamped side of the car. You could 'shave' them but the amount of body work joining to thin pieces of metal would be a lot of work and IMO not worth the trouble. There are many other ways to lower drag before I would worry about that spot.

My GTU car is very heavily modified - little things like the drip rails are now worth considering.

I also need to figure out how to fair the B pillars; aft end of side window openings. I still have slide in 1/8" lexan side windows to use to keep the rain out when sitting overnight in the paddock. I still want to keep the window tracks in the door jambs to hold the plastic side windows, yet I know that they are not very aerodynamic.