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I just put on the OEM stock cast iron intake manifold and installed the new Q-jet and rebuilt distributor. Engine is running very weird and noticed that even without the PCV hooked up I have incredible vacuum in the crankcase. The only thing I did different was put a plate over the EGR port because I don't have an EGR to use. Is covering the EGR ports on the manifold causing me to have a huge vacuum in the crankcase?
I will wait for others to chime in. But the truth is that up around 20 inchesof vacuum creates the most hp and is only achieved by dry sump systems or a evacuation belt driven pump
So your problems are probably related to a vacuum leak. .....
I will wait for others to chime in. But the truth is that up around 20 inchesof vacuum creates the most hp and is only achieved by dry sump systems or a evacuation belt driven pump
So your problems are probably related to a vacuum leak. .....
That's what I was thinking as well. So much for using Felpro gaskets. I've never had this kind of thing happen before.
I believe the crankcase usually has a slight pressure not vacuum, from blowby. So the pcv sucks those vapors into the fuel stream. Usually when guys don't have a good pcv system operational the engine leaks oil from every possible place because of the crankcase pressure. So how do you have vacuum?
No offense intended in this question, but I'm wondering are you actually measuring crank case vacuum or are we talking about intake manifold vacuum?
All I know is we had an extreme amount of vacuum coming from the valve cover grommet without the pcv valve hooked up and it was enough to turn your finger blue plugging the hole. Even my friend who races said he's never seen anything like this. So we pulled the intake this morning to see if the gasket was installed correctly and it was. However, I'm not seeing even crush on the intake ports. There's about a .010 deviation top to bottom. New gaskets are about .095 and in some crush areas I'm seeing .090-.093. That's not much crush going on. Can I use a skiff of sealant on the intake ports while doing the coolant ports?
Problem solved. Never use silicone on the water jacket ports with Felpro gaskets. At least not on my engine. I couldn't get the crush I needed around the intake ports. Yes I'm using silicone only on the block lip seals.
Problem solved. Never use silicone on the water jacket ports with Felpro gaskets. At least not on my engine. I couldn't get the crush I needed around the intake ports. Yes I'm using silicone only on the block lip seals.
When I rebuilt my first SBC (circa 1988) I tried to use the formed wall seals that came in the gasket kit. I had the same issue as you did. They were just too thick and unusable. I replaced with a bead of black RTV instead and fixed the problem. Haven't used those kit wall seals since (I still use some RTV on the water jackets)
From: Arizona - If you don’t know CFI, STOP proliferating the myths around it...
Originally Posted by Big2Bird
Are you using silicone on the China wall vs the gaskets?
IMO, there is nothing wrong with using sealant on the china rails vs. the crap gaskets that are in a kit. I've been using sealant for a very long time now on any engine I've ever built. I use the "Right Stuff" black which works just fine and will seal better than any gasket and out last them as well. Give it a ry and you you never go back to intake end gaskets, rubber or cork. Do not use the Right Stuff on the intake to head unless you never plan on removing the intake, it will be a real issue getting it apart.
Last edited by Buccaneer; May 14, 2017 at 02:12 AM.
Why do I have excessive crankcase vacuum?
