When I bought the CTBNL from my Fairy Godfather (thanks again David) he had done a few tasteful mods and when he took off a stock part, where he could, he kept the removed item. This is why when we I bought the car I also got a bunch of parts in a box, a few larger things that went in the shed in the back yard and some others went on the departing Emperor.
Now that Donna’s retired, the CTBNL is my daily driver and this means that over the summer I have driven home in a few gully washing type afternoon thunderstorms. When this happens, I will invariably have to drive through a few puddles that have formed along or on the road from the overflow of washed gullies. This then washes the underside of the car causing the accessory belt(s) to squeal in protest (they must like water like cats like baths.)
One of the mods David did was replace the large plastic engine undertray (#13 on this Moss Motors page) with a fancy Beatrush Aluminum Underpanel, so one of the large things in the shed was this huge hunk of plastic. I tried to sell it to members of the MMC, but got no takers. I was going to put it up for sale on the Miata Forum, but opted against it because I did not want to have to figure out how to ship it. Now I’m glad I still have it.
The Beatrush panel is slick looking, if you are laying on the ground looking up at it, but I doubt there is any reduced wind turbulence compared to the OEM plastic piece as they claim. The thing is even heavier than the plastic undertray, so that’s not a plus. The only advantage I see is that it extends past the stock unit to cover up the oil pan and on a lowered car this might be a benefit. But the negative aspect is the sides are open, thereby allowing water to bathe the bottom of the accessory belts when fording impromptu bodies of water. The original plastic piece curls up at the sides sealing off the bottom of the engine compartment better.
So when I jacked up the car on Labor day to rotate tires and change the oil, I put the jack stands one notch higher than usual so I could get under the car easier to take off the Beatrush Aluminum Panel and put the OEM plastic piece back in its place. I’m hoping that this might eliminate the squealing of belts when driving through puddles in the future.