Intake Valve Carbon: why not vent PCV to atmosphere?
 

Reading a lot about carbon build up on intake valves and cleaning techniques. Gonna make a diy cleaning wand and vacuum setup this week to blast my valves on the weekend.

Anyway, I'm thinking, if the oily PCV air from the cam cover going back through the intake is the root cause of all the carbon on the intake valves then why not just vent the PCV hose to atmosphere and never have carbon build up again? What am I missing?

tia,

sani

It can be done, but remember, the crankcase depends on the intake manifold vacuum to keep its pressure at or below atmospheric pressure. if crankcase pressure gets excessive, oil thru the turbo stops flowing and you'll burn out its bearings. OCC is the best alternative.

It used to be that excess crankcase pressure was vented to atmosphere - about 50 years ago. To reduce pollution any crankcase pressure is routed into the intake manifold so the vapor and any oil is burned in the engine. For engines with carburetors (remember those?) or manifold/port fuel injection, this wasn't an issue as the vaporized fuel passing over the intake valves kept them clean. Now with direct injected engines there's just air and whatever vapor from the PCV system passing over the valves, so we get carbon buildup.

The solution is an improved system to remove as much oil as possible from the pcv gases - either an OCC or updated valve cover, and then walnut shell blasting of the intake ports as required.

Good answers, thank you. Saving my turbo is a suitably convincing reason. Saving the world, less so.

Follow up question: since the OCC is typically plumbed in to deal with the vac hose on the RH side of the cam cover, how do people deal with the vac hose that comes off the back of the cam cover and goes strait to the intake manifold? I would guess that that hose is causing more carbon build up on the valves than the side exit hose that is typically OCC'd.

That's item 1 in the attached pic:

https://cimg2.ibsrv.net/gimg/www.nor...560d83634b.jpg


tia,

sani

Just read a 9-pager on PCV hose delete. Answered my question. Thanks NAM.

for ref:
PCV Hose Delete


sani

it cannot be done, the crankcase needs negative pressure or you will see oil burn like you have never seen it before

Assume you mean - vent to atmosphere cannot be done.

It appears widely agreed that the rear (or passenger side depending on nomenclature) pcv hose can be deleted and ports capped on valve cover and intake mani. Then the drivers side pcv is spliced with an occ.


sani