Regarding your front chin spoiler;
1. I think perhaps a lot of air is being washed up into the engine bay - not so good of a thing.
2. I've had bad luck with plastic lawn edging, but it was not recessed and protected like yours. Other vehicles were parking by braille and damaging it on mine. Conveyor belt material is the superior choice but is many times more expensive.
3. My shortbox Ford van in the early 1980's I had installed a chin spoiler which did not quite cover the front wheels and stopped a little short like yours. As I recall I still enjoyed the majority of the benefits but there was some fruit left on the tree.
4. Regarding the cowl and chin spoiler, there may be a common aerodynamic treatment for both but I have not yet done it to my truck - see signature links below in my post.
I plan on installing plastic "Barrier Paver Edge" at the bottom of the chin spoiler as a "splitter" for down-force, and at the rear edge of the hood as a Gurney flap.
The Gurney flap just before the windshield wipers will according to an aerodynamicist I met with will kick the air up to meet the lower part of the windshield and not get messed up with the messy part of the wipers and such.................terrible description of what he said, but you get the idea, right?
Conclusion:
If you are getting 1 mpg more now with your chin spoiler, the best you can do is 1.5 mpg. Therefore you are leaving at most 1/2 mpg on the table.
Considering all of the other things you want to do to your truck, I say finish those things up, and by then the existing chin spoiler will require replacing by then anyway -
based on my experiences with that material.
Barrier Paver Edge
