Are the felt ones sound deadening? Imagine the noise smooth plastic would make, especially any debris or stone chippings.
Sound deadening? Seriously?
I seem to recall Call Me Al having some made after quickly burning through his with his lowered, wide wheeled track car.
But it might take some searching to find the post.
I believe that they used the stock ones as a template.
Try from post 36 in this thread:
what do you mean? I could not drive my car WOT for long straightaways or it would trigger a “turbocharger underboost” CEL problem and put me into limp mode. I had to drive all last season that way. With my mod ECU, exhaust and camshafts my engine breathes harder and we think it was too much...
www.4c-forums.com
I haven't had time to read it again, but saved you the search at least!