From what I have been reading, the oil you use and your driving habits are the biggest factors in this carbon buildup if you have an older style GDI engine where no fuel reaches the back of the valves. My understanding is that the fuel is NOT sprayed on the back of these valves in our cars. The video I saw posted in this forum earlier this summer did not answer this question or address this issue.
From the Bob is the Oil Guy forums, oil with a low NOACK is better for our engines. Lots of reading over there, here is just one thread:
https://bobistheoilguy.com/forums/threads/low-noack-oils.312658/ Look up others over there for a discussion on this value and how it contributes to carbon buildup. Synthetic oil alone is not the best indicator of low NOACK.
Low NOACK scores have less oil evaporation that gets circulated, which contributes to less carbon buildup. I did most of my reading on this a few years ago when I had a GDI in my 2014 Rondo. I have also read that having the engine properly warmup will also help, but don't have any proof for you on that but just speculation and info from sources trying to sell cleaners, etc. But if you take frequent long trips that might make this a lesser issue for you.
I'd actually love to see info that this 3.3l engine in particular has gasoline sprayed on the backs on the intake valves. It would make me feel much better but I have not seen any info that shows this.
