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As a modified PCV system would seem to be a potential solution for this fuel dilution problem, I finally got around to investigating more closely what the RX system and others really do. Found this diagram:
RX Dual Catch Can System
Under manifold vacuum situations, I'm sure this system works very well. Low pressure in the intake manifold sucks air in through the catch can and port B which leads to the dirty side valve cover. Fluids will drop out in the can if it is well designed.
However, the value of the system when the intake manifold goes positive (during turbo boost) is less clear. The positive pressure closes the PCV check valve on port C, and there is no flow through this line. In theory the check valve in the A line opens. But if you look at where the fresh air intake comes from, it appears to tap in after the main air cleaner filter. The catch can is supposed to exhaust to the turbo intake. The issue is that for the check valve to open and establish flow there needs to be a pressure differential. Other than for what would be an extremely small pressure drop in the turbo inlet ducting, there is no differential. With no differential the only flow you will get is from piston blow-by. Blow-by pressurizes the crank case and it has to go somewhere. Some will go back up the fresh air intake, and the rest will go to the turbo intake. I'm not sure that is significantly better than the stock PCV system. With the stock system, after the PCV valve closes, blow-by will force flow back through the fresh air intake. Essentially the same thing.
This said, there certainly seems to be some value in the catch cans in retaining oil so it does not go back to the intake manifold or turbo inlet. This almost certainly will reduce coking of the intake valves. However under boost conditions fresh air flow stagnates and fuel is going to still collect in the crankcase.
This is just my conclusion based at looking on the flow diagram. I will stand corrected if that is not the way it works.
Not sure why you think there would be minimal pressure differential in the turbo inlet during boost. Some of us are only tapping one turbo inlet (myself included) and still capturing comparable amounts to those tapping both. I also don't understand your concerns with the fresh air source. While I have not done any oil analysis pre and post catch can install, I do know the strong gas odor when I pull the dipstick is no longer noticeable, and my oil level no longer rises between oil changes. The odor of the catch can contents has a very strong fuel smell. The oil on the dipstick now smells like oil. Since my truck pulls often and my right foot enjoys boost when not pulling, it (catch can) seems to be doing what it's advertised to do. If you still have doubts, I'd recommend the Toyota for you. The Tundras are very capable trucks and you will most likely see comparable mpg's when pulling to the Ecoboost.
Not sure why you think there would be minimal pressure differential in the turbo inlet during boost. Some of us are only tapping one turbo inlet (myself included) and still capturing comparable amounts to those tapping both. I also don't understand your concerns with the fresh air source.
If you compare the downstream side of the engine air filter to the turbo inlet, there is nothing but a large duct between those two points. Aside from a very small pressure drop due to flow there is going to be no pressure differential to enable fresh air flow through the engine. The blow-by flow is likely to become the dominant source of pressure differential. It hopefully is not very large, and the positive crankcase ventilation is essentially disabled.
If you compare the downstream side of the engine air filter to the turbo inlet, there is nothing but a large duct between those two points. Aside from a very small pressure drop due to flow there is going to be no pressure differential to enable fresh air flow through the engine. The blow-by flow is likely to become the dominant source of pressure differential. It hopefully is not very large, and the positive crankcase ventilation is essentially disabled.
Phantom had both this set up and an external filter set up. So he should know by how much each set up ventilated.
I have no idea what he has. My comments were about the standard RX setup for a F150 EcoBoost.
If you read the other catch can stuff you would see all of this has been covered. Phantom had his clean air come from both the air filter and from an external air filter. Read his catch can thread.
09-30-2014, 12:11 PM
