The Stovebolt Site Forums The Shop Area Engine Shop Intake Gasket

I know that you guy's deal mostly in th older stuff but maybe you can still help me.
The problem is on my Pro street '72 chevy.
I have a 502 in it with a blower and NOS. :p But about every 250-300 miles I have to replace the front and rear intake gaskets A real pain in the b**t ! Any ideas what the problem might be?
I've replaced the intake once thinking that would fix it.
I built this motor myself and had the block gone over very carfully by my machinist. Thanks

Are you talking about the end valley gaskets, facing the firewall and radiator? If those are going out and blowing oil then your pcv system needs help. The problem is the forced induction- you are getting more blowby than the engine would normally aspirated. You probably need a pcv valve and breather filter in each valve cover. You will need a check valve between the PCV valves and the vacuum source that you hook it to so it doesn't pressurize the crankcase when the engine is under boost. If you have a drawthrough setup put the pcv intake between the carb and the blower. That should help.

In addition to what 4ontheFloor said, you might try using a bead of black or red rtv instead of the rubber gaskets. This is especially helpful if the manifold or heads have been machined.

Here\'s a thread (on another board) that might have some useful info on this subject.

Hi
Yes these are the gaskets facing the firewall and the radiator.

I only have 1 PCV valve in now so I will try to get a=nother on in this weekend.

I have tried the rubber, cork, and also just R.T.V.
The machinest thinks it's the manifold.What's the chances of getting two bum manifolds?
Well maybe the pcv will fix it.

Thanks Guy's
Jim

Before getting another manifold, try the RTV and a second pcv. Let the sealant cure for 24 hours before starting. I would also tie in a vacuum gauge to the intake manifold vacuum source, and, if you can rig one up to the crankcase, use a gauge to check the pressure there. I agree, the second pcv should be a big help. It is possible to get two bad intakes, but I doubt if it happens very often.

Thanks guys.I'll try to get it done today.
This is the fourth thime i've done this
Thanks again,
Jim

Lowboy: need more specifics on your set-up. Something seems wrong with this picture. A 502 on the street on pump gas, must be a smaller unit and/or set up with minimal boost? Why? What speed is the blower turning (ratio) to the crank? And why a fogger on top of that? Set at what boost?
What type of blower manifold do you have, and how is the gas system plumbed to it, to the hat or the ports? This can be done differently on different manifolds be they BDS, Weiand, Hampton, or whatever. What is the rating of the pop-off valve, and is it functioning properly? What type of boost controller are you using? And set up how?
On the street, a turbo/NOS system is far easier to control, adjust, service and maintain than a displacement blower/NOS system. Do the problems begin when you try to use both blower and fog at the same time? Also I never did ask what type of fuel system do you have, FI, or carbs?

Some other thought's -

Stock headgaskets are stainless, and about .042 thick, I think, but not sure. Have you checked the ones you have on at present, for thickness as compared to stock. Thicker gaskets will lift the manifold right off the block. Was the block decked? Or the heads milled? This will also cause interference/fit-up problems. Was the blower manifold purchased "new", or is it used and possibly warped. Some of the alignment and fit can be corrected with careful inspection and the addition of eccentric head dowels and/or bushings to allow the heads to move fore/aft or lower on the block. This fit is extra critical to prevent a blowout at the rear/front of the manifold, as this is the weak spot with no bolts to hold it down to the block. I feel that maybe this is whats happening when the engine heats up and all parts are fully expanded, causing a weak seal on the front/rear valley areas. This can be easily aggrivated when the NOS blast may "spike" at 35psi or more against a weak manifold surface. The NOS nozzles need to be as far down the intake valve port runners as practical so as not to cause turbulance problems in the very small air box (plenum) that sits in the manifold base. The plenum has enough troubles dealing with the pressure waves of the rotors as things are.

Something sound suspect to me concerning your manifold. I think you shuld contact your
nachinist and check things out. Just my 2 cents.

Think Chevy!
:p :confused: