The carbon is so thick and baked on that you can't remove it with a scraper, without also scratching the metal.
I had used Carbon–Off (which dissolved the carbon without touching the metal), but the EPA, in its desire to save us from ourselves, took the main ingredient off the market last June, so I'm back to several applications of oven cleaner and hot water rinsing.
Five minutes of ZEP oven & grill cleaner and five more scrubbing with the brush under hot water does the trick. Unfortunately, the carbon is so thick that the oven cleaner can't get to it all in one shot. I'd run it through a hot tank, if I was taking the head to the machine shop, but that's not economical for just the intakes, and the shop isn't close by.
I'm going to run it throught the blast cabinet with fine glass afterwards, because I want it polished prior to the Cerakote that I want to cover it with. I did this on the last intake I cleaned, but I used VHT paint, becasue I couldn't find a local Cerakote applicator with an oven large enough for both halves at once. I have one in hand now, so I'm looking forward to a clean, polished intake on this job. The cabinet gun can't get all the way into the runners, so a cleaner and brush is necessary.
The VHT did OK on the intake, sucked on the exhaust, but I wanted to try a ceramic coating to compare. It's several times the cost of the paint, but I'm hopeful the appearance makes it worth the cost.
