I have also used the Mopar cleaner directly down the plug holes on top of the pistons. Saturate it pretty good in each hole...let it set for like 15 minutes. Put the plugs back in and take it out on an aggressive run. It will smoke like hell but should clean some of the carbon off the pistons and rings. This along with the in carb method actually raised the compression of my 318 Poly a little bit. You should change your oil after you do this. The Mopar stuff is not re-labled Seafoam. Works a little better IMHO.