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Postby jlj1267 [OP] » Dec 01 2019, 9:16pm

So I’ve been doing a lot of intensive research on the intake manifold/PCV system on these engines. I’m getting fed up with oil consumption and I’d like to share what I’ve found. The intake manifold has an integrated PCV system (no PCV valve), in which crankcase vapors are pushed through a small tube on the belly of the intake. The gases fill into the intake where they are then cooled by a stream of air coming from the PCV inlet port (5/16” hole in throttle body). Below I’ve attached an image from GM explaining how a typical PCV system operates. Their manifold-integrated PCV system, which has been used on many different GM engines, do follow the requirements instated by the typical operation of an efficient PCV system, however the oil gets trapped into the intake, where it is slowly burned due to high intake temperatures. The manifold acts as the oil separator, and in a way serves as a sort of “catch-can”. This shows that GM has designed this intake to in-fact, trap oil inside the intake, to separate crankcase vapors, an issue many of us have had to deal with upon removal of the intake or replacement of manifold gaskets. But GM never acknowledged this as a problem. They put out TSB’s for new manifold gaskets and bolts and yes, they helped slow consumption. But the only way to stop oil from getting into the intake is to run an external PCV system. Some have been able to weld a 45° tube on the small tube under the belly to keep oil from splashing up and being sucked in so easy, but this only slows consumption. Others say you can add a check valve to the tube. But once again, this only slows it. The true fix would be to pull the intake, cut the belly open and do the normal modifications inside while you’re there with the manifold off. Cut the tube off and weld it shut. Then on the throttle body, tap the small 5/16” hole and plug. You must be sure to of course clean the intake spotless before setting it back on top of the engine. As for the PCV, you can either tap the valve cover for a PCV valve, or on the rear of the manifold next to where the EGR housing bolts down, you can weld a bung, and add a PCV valve. Then on the neck of the intake (driver side slightly under throttle body) weld another bung and add a barb fitting. Run a hose from the barn fitting to the PCV valve either in the valve cover, or on the back of the manifold. Hope this clears up a lot of headaches for people. I’ve been looking for a solution for over a year now, and have finally designed something that will work. I plan to run y’all traditional style big block valve covers with breathers, so welding bungs, tapping the intake wouldn’t have to be done. Just plug the factory ports and add valve covers with a breather. Thanks!
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Postby zdatyukon » Mar 22 2020, 3:27am

Hello, interesting post. Have you performed the mods described in your post? Please be sure to report back if they worked as planned.
I am getting ready to do the intake manifold gaskets to see if it will reduce consumption.
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