I finally got my undercarriage of my 1970 Challenger (Hamtramck built) in first primer this weekend. Since it was not the final priming/ painting (I will be going for the factory original look), I thought I would try to using a mixture of primer that has been floating around on the forums as something that reflects the factory correct color. I think it originated from an old Mopar Muscle article. I first tried 2:1 of DP40LF : DP90LF as the first coat and found it to be way to dark. The next coat I tried 4:1 of DP40LF : DP90LF which is what you see in the picture here. The actual color is darker and more blueish than what you see here(For reference contrast the rest of the car is in DP40). There is no way that that either mixture of DP40LF/DP90LF) is correct either. Maybe the formulas I've been seeing are for the non-LF versions of the primer. I didn't really want to, but I might try the undercarriage paint from Resto Rick. What do you think? -Chris