I'm 'bout to throw on my intake on my 94 351W. When I removed the manifold, I noticed it had a rubber/silicone gasket under the intake for the valley seal.

I purchased the fel-pro top end gasket kit and it came with cork ones instead of silicone. Do you think I should upgrade to better gaskets or should the cork be fine?

 

I don't use any gaskets on the ends. I lay a thick bead of black rtv on both ends, then set the manifold. this never leaks, although it makes it a pain to take the manifold off later

 

cork gaskets suck if you use one at all then spend the money and get the better ones, it will be worth it in the end

 

Yes use the cork gaskets, just clean the block where it mounts and glue it down with contact cement. Then apply RTV to the corners and a bead across the top and mount the intake, you'll have no problem with the gasket getting displaced now or in the future and therefore no leaks.

 

I and any other pro builder will NEVER use any gaskets for the valley ends, and neither should you, here is why.

The gasket (both cork and silicone) has a thickness and must be crushed a certain amount to seal. This is true for both the valley and intake gaskets. But because of the difference in angles between the valley and head, and the fixed distance between the heads, it is almost impossible for all these angles and pressures to come out right at the same time.(even more so after machining or rebuild) So which do you want to have the better seal, the valley or the heads, the heads of course. So throw away the valley gaskets they can only hurt you.(all of them) They will either hold up the manifold causing a manifold leak. Or they will not have enough pressure on them because the heads are holding up the manifold and they will leak.

The solution is to use a quality RTV. It will stay soft enough for you to get perfect pressure on the heads and then harden and seal until the motor comes apart. I have a favorite RTV that I always use for this job (and many others) I HIGHLY recomend you get some and use it. It is called "RIGHT STUFF", is made by Permatex (my favorite brand of sealers) and is a quality RTV that is rather thick and sticky so it stays put, and even better it comes in a pressurized can that works like Cheese Whiz. This makes it vary easy to lay down a perfect bead. (Tip, put a 7/16 box wrench over the nozzle to use as a lever/trigger for the can)

Just lay a bead on the engine block valley edge about 5/16 high, making sure to get it in the corners. Sometimes it helps to first put a thin film on the block and the manifold before laying the bead and placing the manifold, this is cause it sticks to itself better then the metal. When you install the manifold it will push the RTV flat and ooze out the sides to create the perfect gasket.

Also, make sure to use some RTV around the water passages in the heads and manifold, it is not needed around the intake ports but is good insurance around the coolant passages. You may also find it helps to glue, the gaskets to the head before installing the manifold, this will help keep them in place while your putting on the manifold. (a perfect use for Permatex #2)

Hope this helps, have fun.

Just another 2 cents.
In my opinion and experiance you can do every automotive sealing job with just 2 products. Right Stuff, and Permatex #2. #2 is a great general sealer that works so well you won't get the stuff off your hands for days. You will never find a tool box of mine without these 2 products.