Just a few weeks ago I had my intake off so I could gasket match the upper and lowers, and noticed the intake valves looked horrible. I cleaned em up a little, but ran out of time and had to leave 'em lookin dirty. Question is, can I clean them with the intake on the car, IE a tank additive or something. I have heard many people ranting and raving over a product called BG44K, but at $17 a can I don't know if it'd be much better than an off the shelf. I have ran 3-4 cans of techron through before this and they're still dirty. Also my freind told me about water injection through the intake, and that'll clean out the cylinders and all. He compared it to a car with a blown head gasket and the leaky cylinder has all the carbon cleaned from it.