Our manifold vacuum-induced combustion cleaner is Berryman B-12 Chemtool Total Combustion Cleaning Kit (part #2610) and comes with a hose kit for introduction via the PCV valve or the brake booster, depending on which is more appropriate for your vehicle’s vacuum line configuration. 2610 has not yet been tested on direct injection intake valves but is expected to have good efficacy as it has been shown to clean both traditional valve buildup as well as combustion chamber deposits. If your rings are in good shape, i.e. if you aren’t burning oil, then changing the oil after applying 2610 should not be necessary. As for the plugs, 100% of the components in 2610 are combustible, so there is no risk of fouling or otherwise damaging them. Regarding a piston or cylinder soak, Berryman B-12 Chemtool Fuel System Cleaner (part #0116) is ideal for this task. Just remove the spark plugs and pour in enough B-12 Chemtool to cover the entire piston. With V-configured motors, we recommend jacking up one side of the vehicle to bring one bank of cylinders to a more vertical orientation and thereby cut back the amount of product required. Depending on the diameter of your pistons and the orientation of your cylinders, it may take nearly a full bottle of 0116 per cylinder to ensure that you cover the entire crown. Note that Berryman B-12 Chemtool Fuel System Cleaner is also available in a 1-gallon size (part #0101). As for soak time, it shouldn’t take very long. Because the product is so aggressive, you likely won’t see any additional cleaning much passed 30-60 minutes per soak. At that point, you should use a turkey baster or small diameter tubing to remove the spent carbon/B-12 Chemtool mixture. If buildup is severe, you may need to resoak a time or two until you get clean product out of the cylinder. Lastly, B-12 Chemtool Fuel System Cleaner is not harmful in the crankcase and is in fact an excellent cleaner in that arena, too. However, if you have much leakage (more than a couple ounces), you should run the car for 10-15 minutes and then change the oil and filter just to be safe. As with the 2610, if your rings are in good shape, then you should not need to change the oil after performing a cylinder soak. While we specifically make an Oil Change Flush (part #1216), 0116/0101 is a very versatile product is often used as an engine flush, too. To use it in this manner, pour into your cold crankcase approximately 1½-2 fl. oz. of B-12 Chemtool per quart of oil capacity. If your vehicle holds 4 quarts of oil, then you should use about 6-8 fl. oz. of B-12 Chemtool. After you’ve added it to your cold engine oil, start the vehicle and run it at idle 10-15 minutes or until the oil is warm. Then change the spent oil and replace the oil filter.