Any carbon cleaning treatment needs to be applied directly to the valves as that is where the buildup is. This isn't going to happen using a fuel additive with a DI motor. Actual mechanical cleaning or application of a chemical type cleaner is whats needed. The best way to keep carbon off the valves is drive the car like you stole it.....😀I shall see if the liqui moly intake valve cleaner product does make an improvement (doing a second treatment this week). Only way easy way i can check is a do a 0-100KM time check compared to some past numbers. Ideal would be a have a look at the intakes with a camera or do a dyno. The way im thinking (walnut blast cost is about what...$250-300)
is take the cost of a blast and have the intake ports polished and enlarged for $400+ (hp gain 20+). LArger intake polished port may reduce eventual build up. Only old argument i see is that polished ports may reduce fuel / air velocity in lower rpm, which lowers torque, , but thats on non direct injection engine. Food for thought
You can't really do much with the intake ports. There is a coolant jacket around the bottom of the port, and the wall between the port and the coolant passage is very, very thin.
0-60 times mean little here. Unless you have very accurate timing equipment and are able to repeat runs very consistently under the same conditions, a few tenths of a second difference that may or may not be caused by dirty valves won't be noticeable or meaningful.