My next mod is to add 4"-6" strakes between the rear tires and the diffuser to clean up the air going through the diffuser. I may extend it to curve close to the front of the rear tire to block some flow to the tire.
something like this:
I will re-use the 6" lawn edging I removed from the air dam, I have to find a good way to attach it to the coroplast. I probably will have to remove the undertray to put a steel stud reinforcement strip to hold the strakes in. The coroplast is curved and the lawn edging doesn't curve well in that direction. I will try the heat gun and stretching the bottom edge. The exhaust tip is rattling on the metal diffuser opening and I will bend the metal up.
The center strakes are really for structural support to keep the curved surface and are not doing anything with the air flow. I probably will cut those flush.
But first I have to figure out what is rattling and scraping while driving. It gets louder as I go faster, so it has to be the wheel. Sounds like right rear wheel. Doesn't look like the skirt is rubbing.
Unfortunately I did not refill my tank and get my gas mileage before my heater core job. Didn't occur to me that I would lose my odometer reading when I unhooked my battery and removed the instrument panel. Rats, I had at least 650 miles on the odometer, probably closer to 700 miles.
And double rats that my blend door for the heater is hanging up and I still have some heat on in the car while driving. There is no way in hell I am pulling the dash apart again. I may just bypass the heater core until it gets cold out, then hook it back up when it gets cold.