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Blow by

Doc Harley

TY 4 Stroke God
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'17 Sidewinder LTX SE
I've spent some time researching "blow by". And found this to be 100% true in automotive applications. Anything with forced induction is going to experience blow by. The more boost, the more prevalent it becomes. The PVC system on most cars, due to EPA regulations, require the regurgitated air mixed with oil to go back into the intake system. Which everyone in the automotive industry tries to prevent. Vented catch can, oil separator, etc.
The 998t has a vent on top of the valve cover that pushes that same regurgitated air back into the intake. Intern bringing with it more deposits to the valves and intake.
Is there nothing we do to prevent this from happening?
 
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Some (like myself) bypass the intake and dump it on the ground where it once came from. Some will fit a catch can. When I did my bypass there was a big pit of oil in the intake ahead of the turbo. Took it all apart and cleaned all the hoses, never putting that PCV hose back there. The bypass also keeps that oil out in case you roll the sled.

Have a quick skim through this:

 
I've spent some time researching "blow by". And found this to be 100% true in automotive applications. Anything with forced induction is going to experience blow by. The more boost, the more prevalent it becomes. The PVC system on most cars, due to EPA regulations, require the regurgitated air mixed with oil to go back into the intake system. Which everyone in the automotive industry tries to prevent. Vented catch can, oil separator, etc.
The 998t has a vent on top of the valve cover that pushes that same regurgitated air back into the intake. Intern bringing with it more deposits to the valves and intake.
Is there nothing we do to prevent this from happening?

You answered your own question. If you are concerned about the oil, use a catch can/separator for the PCV line. It really is more of a concern with direct injection engines. Note that the link above is about the roll over valve, different thing altogether.
 
Even NA engines have blow by. Piston rings don't seal any cylinder 100%. There's always a small amount of compression/cylinder pressure that leaks past. Same goes for valves, valve guides, valve seals.
By itself, normal blow by is not a problem. But it carries oil and other contaminants with it. As you state, there are a few ways engine manufacturers manage it. And yes, more boost equals more blow by.
Many factors affect it. Best we can do is to do our best to minimize it with the basic engine and system design we have. And, keeping engine parts in best state. Getting best possible ring seal starts at break-in. It's why Knapp says when breaking in, ride it like you stole it! You need high cylinder pressure to force rings against cylinder to seat them. Aside from that, make sure valve guides and valve seals are best they can be. Run right oil and right amount of oil (don't overfill). 998 dry sump system helps allot too.
 
You answered your own question. If you are concerned about the oil, use a catch can/separator for the PCV line. It really is more of a concern with direct injection engines. Note that the link above is about the roll over valve, different thing altogether.
Not concerned, just wondering if anyone feels the need??
Just after writing this I went and checked my air filter elbow, nothing in there. I'm kind of surprised?!?!
Even NA engines have blow by. Piston rings don't seal any cylinder 100%. There's always a small amount of compression/cylinder pressure that leaks past. Same goes for valves, valve guides, valve seals.
By itself, normal blow by is not a problem. But it carries oil and other contaminants with it. As you state, there are a few ways engine manufacturers manage it. And yes, more boost equals more blow by.
Many factors affect it. Best we can do is to do our best to minimize it with the basic engine and system design we have. And, keeping engine parts in best state. Getting best possible ring seal starts at break-in. It's why Knapp says when breaking in, ride it like you stole it! You need high cylinder pressure to force rings against cylinder to seat them. Aside from that, make sure valve guides and valve seals are best they can be. Run right oil and right amount of oil (don't overfill). 998 dry sump system helps allot too.
Very good read, Turboflash...
 


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