Brand new to the site. Building a 71 Cutlass with a modified 455/350 trans. Have been breaking in the engine and am having what I believe to be a vacuum problem. My rear intake manifold gasket is pulling in toward the engine and tearing. I have some vacuum lines plugged from the quadrajet and 4-5 others hooked up. Engine is on the frame, so some can't be attached. I tried some different combinations with lines, but can't seem to locate the problem.

 

Are you using a PCV valve.

 

Yes, am now. The first start on the engine both front and rear seals pushed out.

 

Welcome to CO. I am going to move your post to the big block forum, perhaps you will get a little more exposure there about your specific problem. It might be that the end seals are slipping if you are using silicone and not letting it set up before you place the manifold on the block so they slip at that time and really aren't being sucked in after the engine starts. We have quite a few threads on intake manifold gasket installation with quite a few recommendations and different approaches. Good luck.

 

You might try removing the intake and dimpling the front and rear rails with a punch before installing the rubber end seals. This will allow silicone to "bite" onto the engine once it is cured. I did the same on my 455 and it worked great.

 

Welcome aboard

 

I quit using the rubber end seals, RTV works good and lasts a long time..

 

I never had rtv only seal well for me,I usually apply a small amount of rtv to both eng rails and install both end seals,let it set overnight and then apply another small amount to the top of the rubber seals and install the intake. I let that set overnight and then have always been good to go.

 

What you just described I did on the last start. Pulled in rear seal pass side. First start pulled in front and rear after 10 min running time. The different between the two was I changed some vacuum lines. I figure there is something I'm overlooking.

 

if you are running a pcv on one valve cover the only way it could suck in the intake end seals is if the opposite valve cover did not have a vent or the baffle in the valve cover is plugged. the pcv valve is creating vacume in the motor but if you pull a vacume in one place you have to supply air into the engine somewhere else.

 

Interesting. I have a baffle/vent on the driver side and a PVC to the carb on the other side. Not sure if the baffle is plugged, have to check it.