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ok people you're all overthinking the catch can thing.
Follow the KISS principle here.
Snake oil, yes mostly.
Let's get back to basics.
First of all how does wet oil cause coking on a valve seated above the combustion chamber?? Coking is a result of combustion gasses, not motor oil.
Secondly these are 4 stroke motors, INTAKE/COMPRESSION/POWER/EXHAUST.
On intake, intake valve is open, sucks in air(fuel is now direct injection). Compression both valves closed, power(controlled explosion), exhaust, exhaust valve is now open.
Now gas burns at a constant rate, no magic pill changes that. Higher octane allows for less pre-detonation(means boom before you want).
Now they've tweaked these a lot over the years, but there's still valve overlap between intake and exhaust cycles. So you've still got some unburned gas that can escape. Yes modern tech it's miniscule but still there. The higher RPMS the more likely you'll see overlap because once again, gas burns at a consistent rate but higher RPMS causes more opening/closing during a minute. So still burning fuel can back into the chamber due to pressures which is what is most likely causing the coking.
Now take those who pump 91+ octane in a motor not tuned for it. Now spark is adjusted with ant-knock readings, temp sensors, cam position sensors etc. But it's estimating the best time to ignite with a 87ish octane. Premium resists ignition and without a stronger spark or adjusted timing like with a tune, you're just adding a little more out of chamber burning, once again at higher RPM's, it's worse when a car isn't properly tuned for it.
So bottom line, it's unlikely to stave off coking. Running an improper octane on a GDI engine isn't good for it. Running higher RPMS more often will increase the chances of escaped gasses.
Now this is just my opinion, i'm no freaking genius, but i've worked on enough motors to see valve overlap and I know these cars are fun to drive and drive fast and hard.
I also know many people think premium fuel in our cars will somehow know that it's a 'slower burning' fuel. It won't, if it did our engines would be flex fuel rated and be setup that way since E85 has much higher octane.
Now tuners, such as overkill, adjust timings to compensate. Your stock ECU.....i doubt it's looking for it or knows how to compensate unless the anti-knock detection is going off but that's 180 from what I believe is causing this coking.
Now the catch can, will keep the motors from ingesting a few ounces of oil which will keep the plugs cleaner over time, giving a better spark and true to life expectancy. Beyond that I can't speak much to how they really do us any good.
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