I'm not concerned with decreasing the inside diameter of the tube, for a couple reasons. First, I've had them blasted and that has taken much of the bumpiness off of the inside. Second, with the coating, it will further smooth out the inside. That results in less turbulence inside the tubes. That means faster velocity and higher CFMs. It may not be by much, but every little counts. And just curious, have you ever touched the lower tube where it mates with the plenum? That's pretty hot when the car is warm. I believe this will have much the same effect of having the tubes extrude honed, but at a much more reasonable price. And you get the added insulation factor. Bottom line, is for less than what it costs to get one of the tubes extrude honed, you can have a pair of IC tubes coated inside and out for a chrome appearance and insulated. Besides, it's going to be a while before I have the $ for the custom IC that I want. It's not the #1 thing on my list right now. I'm just replacing the power steering pump and front suspension, so while I was at it, I was going to replace the IC tubes with these as well.
I"m not sure what it would cost to have the stock tubes and these tubes flow tested, but it may be worth it just to get some #'s.