Are Subaru’s direct injection or port injection? If you raced them I assume engines were frequently disassembled, cleaned and reassembled? So your advocating allowing the oil mist and vapors to go ahead and coat the backside of the valves so they get caked with carbon deposits? Plenty of videos and borescope footage to show what happens to our engines out there. Now how much performance or fuel degradation occurs for the average Joe who changes cars every 3 years or so, probably a subjective discussion.
First, the way that I feel about forums are for people to share information and experiences. Me telling my background was not to toot my own horn but, to give a understanding of my point of view. If it was taken that way it was not my intent. Now let me answer your response. You said a lot so, let me do my best answer in order.
No, the Subaru’s were not GDI they were port injected. After your comment, I started doing research to see if I was not understanding the differences with GDI that made catch cans necessary. I found some interesting things. More on that later.
Yes, I tracked (and street raced in my youth) cars that I have built from my ’69 Mustangs w/ 351 Cleveland, 390 big block, my’ 56 Ford w/ Chevy 327, ’70 VW bug w/ 2.8l Ford V6 hanging out the back mounted to a VW drag tranny built when I was17yrs, Honda civic, and a ’05 Subaru Legacy GT 2.5L wagon that I modded, tuned, and dyno’d at over 370whp on e85 I had for 10 years as a daily driver, just to name a few. If I was racing professionally where .1 of a sec was important it may be necessary to rebuild every race. But, I build my engines to last. I might tweak a thing or two but, not a full tear down unless something goes wrong. I don’t abuse my engine and take them past their limits mechanically or by tune. Also what is your hands-on practical experience with engine building and tuning so, I can better understand your point of view?
Next, nowhere did I “advocate on behalf of oil mist or vapor coating valves and taking power.” Here is my point. To only blame the oil mist from the PVC for carbon build is a bit short sighted and not looking at the whole picture and all the things that are going on in the engine. That is why I asked about your hands on experience with engine building. You have several things that can lead to build up on your intake valves since you don’t have the fuel from the port injector to clean the valve
These are just a few
You have:
Oil leaking pass turbo seals
Oil leaking pass valve guides
Contamination from combustion chamber when valve is open (engine cams have overlap where intake valve can be open for a period during compression strokes)
EGR (Exhaust Gas Recirculation) : It sends exhaust gases which can have particles from the engine back into the intake and can cause build up . I can’t find definitively if this car has one.
I found a video from "Engineering Explained" that covers the facts I stated above. I found it very informative.
After my research my opinion hasn't really softened toward catch cans. Because catch cans do stop some but, it doesn't stop any of the other things that can cause carbon build up that I listed above. So, you will still have carbon build up with catch cans. I couldn't find anything except for advertisements that shows how carbon build up is cut in half over a period of time with catch cans or something like that. If you or anyone else have any info, I would love to see it. I feel you can never stop learning.
Also do catch cans void your warranty?
Thanks
Sorry for the long post.