Originally Posted by quint
I definitely think with catch cans, the question isnt whether or not they work, its whether or not they matter.
I had the intake of my dads Corolla at around 280,000 miles trying to diagnose how sluggish it was, and I probably scraped enough oily wet carbon out of the intake tracts to fill up Rosie O'Donnell's mouth, it was horrific. The difference that made was night and day, it drove like an entirely different car once I got all of that junk out. I couldnt believe how much gunk I got out of that thing.
I had the intake off my 240sx at around 220,000 to replace the leaky hoses under the manifold, and I dont think I got enough carbon and crud out of it to literally fill a thimble. There was simply nothing there.
Would a catch can have mattered on the Corolla? Without a doubt, in my opinion. Would it have mattered on the Nissan? Not one bit. On most cars, I think they are nothing more than a solution looking for a problem.
I disagree as mentioned in his other video where he says that OE's are aware of valve deposits being a problem and they don't like talking about it. I would agree with you on the engines that use PFI or PFI in addition to DI to combat this problem or in Mazda's case where they keep the valves at a higher temperature to deal with oil not able to form deposits as was mentioned here previously.
Here is the other video I referenced with Jason from Engineering explained where he touches on valve deposits in the video:
https://www.youtube.com/watch?v=66C4YIiwRbM