The shop I use (
www.machdevelopment.com) uses coatings extensively and has documented the improvements with both dyon and track results. From memory I believe a SBC stocker gained .04 with full coating to an intake topside and bottom side. Topside is heat rejecting and bottom side is oil repelling. The same has been done to my parts. And I'm sure many won't believe such claims and I myself can't substantiate the improvements because I've always had the coatings when & were allowed. I do know this, icing the intake of either my cast iron stocker or aluminum SS intakes have never seen the same results as I see on un-coated intakes.
Check the website I posted. There's an interesting story on Bud applying coatings to a model airplane engine. And the shop just did the entire drivetrain of a vintage 4 cylinder road racer. The lap times picked up an incredible amount and I guess the guy was beating cars he couldn't even keep up with before.