Always was quite pleased with Bore Tech C4 Carbon Remover. Price is high so I'm always looking for something to at least run through the barrel for the first few passes that might cut down on the amount of Bore Tech used. Engine rebuilding has been my career so I have access to lots of cleaners which I have tried to varying degrees of success or failure. Techron, Seafoam,GM top cylinder cleaner, BG products, various Mercedes supplied cleaners, etc. Found it a surprise that PB Blaster actually does a very acceptable job as a product to run though the barrel and have better results. Of course this is based on the results of the color of the Bore Tech patches that finish the job, which come out cleaner than with other products I tried, not scientific but for me it works well.