Do our intake gaskets ever really seal ???

You need to use something like Permatex "High Tack" adhesive spray on both sides of the intake gaskets, then bolt down the intake while it is still sticky. They essentially need to be glued into place.

In the case of a naturally aspirated engine, the gaskets do not need to hold 30 psi. The most they are going to see is what shows on the vacuum gauge.

Inches of mercury are going to equate to psi, or very close to psi. Vacuum is negative psi.

IF you were going to "pressurize" the intake with a supercharger, then that is a different story. I'm sure that there are better material gaskets, i.e., stronger, but I've done fine with the standard Fel-pro gaskets and the "high tack".

The Hall Weber manifold for the 351c is not particularly susceptible to leakages and is a rugged design. It is a reinforced copy of the original Detomaso manifold. I'm not sure why you should be having a leakage issue?  I've never experienced that with this engine and this setup?

For the sake of discussion, the most boost that I have dealt with was 28 psi on a turbo charged engine and there were no issues with the intake gaskets leaking but the connecting hose from the throttle body to the intake manifold was unreliable and would disconnect itself (blow off) regularly.

Steve - perhaps I am not following the test set up?  you were testing your fuel injection connections with 30 psi for all the feed tubes?  That air has to go somewhere so I am guessing it forced its way past your intake gasket which was probably fine.  As Doug said, the intake is in vacuum.  If your engine is pulling say 17 inches of Mercury, that is only about 8 psi of negative pressure on the intake gasket.  I would be concerned you blew it out with that test.  But then maybe I am not following the test rig completely.  Also, if the fuel runners never really saw that pressure, is the tubing test valid?  Lee

Ideally I would be testing the black tubing and connections with vacuum instead of pressure but I am not setup for that.  It is fairly easy to test for pressure leaks with soapy water.  The lifters are not yet installed and all of intake valves are closed.  The entire manifold holds 30 PSI but it leaks out within 20 or 30 seconds.  The only bubbles are along the gaskets and not around the black tubing connections.  I can also hear air escaping from under the manifold.  I don't think I am getting correct seating of gaskets between the manifold and heads.  I don't think the gaskets slipped because they were glued to the heads with Right Stuff.  I will pull it apart and try to isolate the root cause.  I think the gaskets can readily hold 30 PSI when everything is matched up and sealed.

The Felpro 1228 gaskets are $32 a set.  The Tim Meyer gaskets are $17.35 a set.  I receive five sets tomorrow.  Hopefully I don't use them all up figuring this out.

https://www.tmeyerinc.com/product/gasket-intake-4v/

The best suggestion is to go with a smoke test. The worst part of that for me is the strange smell it leaves from cooking the vegetable oil to make the smoke. It lingers for about a week.

Logically I would say that it is impossible for the gaskets to now be leaking but frankly I don't recall ever seeing a chart with a number specifying the maximum pressure that intake gaskets are expected to hold?

Quoting from Shelock Holmes on the scientific method of "deductive reasoning", "when you eliminate the obvious, whatever is left must in fact be the answer".

To me, that simply means you have exceeded the holding pressure that the intake gaskets are designed for? Sorry to state the obvious.

I did a while back have a set of intake gaskets I got from my engine builder that were hard, not soft like the FelPro's. They seemed to be an "asbestos" type of material? I had them hanging on the wall in the shop for a couple of years and when I went to move them, they broke due to lack of flexibility. I never saw another set like that.

I would also have to add to the list of considerations of possible causes, "resurface the heads", but I would need to see with my own eyes if even the stock "turkey tray gasket" could cause this? Your description indicates multiple leaks which to me makes no sense whatsoever?

You win the prize of "I stumped the 'Peanut Gallery' "! Congratulations!

I took it apart and used a flashlight to check for gaps between the manifold and the heads.  It looks like the angles are correct and the manifold looks like a good fit.  I started looking for cracks and did not find any.  However, the surface of the manifold where it contacts the heads has fairly deep milling marks.  They may be the source of the soapy water air bubbles when I installed the manifold on dry gaskets.  They may also be the reason I can hear air escaping on the bottom side of the manifold.  It looks like I may have about 1,000 tiny air leaks because of the grooves.  The depth of grooves are similar to a fine file.

‘The death of a thousand cuts’…

The question is - is it severe enough that it will adversely affect performance…

I would think that could be sealed with a gasket sealer… and am surprised the gasket doesn’t do it!

Show me a picture of how the gasket sits on the intake manifold.

Here is the photo.  I can now see that there is a problem with alignment of the gasket bolt holes.  The misaligned bolt holes in the gasket are shifting it to one side of the intake runners and thus reducing the amount of gasket one side of the runner and covering the opening on the other side.  This has not been on my radar screen and may have been working against me all along.  A misaligned gasket on top of a serrated surface on the manifold is asking for leaks.  Hence the reason I asked "Do our intake gaskets ever really seal?".

This is a Felpro 1228 gasket.  It needs the bolt holes elongated on one side for it to work.  My new Tim Meyer gaskets have bolt hole alignment issues as well.

It looks like each time we install a manifold we need to check alignment of gasket's bolt holes and intake runners on both the manifold and the heads.

Doug, what else do you see in the photo?  Thanks!

@stevebuchanan posted:

Doug, what else do you see in the photo?  Thanks!

Other than the gasket is taped on backwards.  The blue "Print O Seal" goes against the intake, not the cylinder heads.

That is a lousy fitting gasket. You need one that fits flat and aligns better.

I do not think that the machining marks in the intake are an issue at all.

Not only should the gasket align much better but it needs to be soft so that is compresses as you tighten the intake down.

The gasket IS the issue. I haven't looked for a gasket recently so I am not aware of what is available but I am thinking that something as simple as the plain-jane Victor without the Printo-o-seal is likely the best fit.

Looking at the first picture of just the intake, the impression left by the gaskets on the intake seem to indicate that the Print-o-seal ring is the issue. It is in fact overlaping or at least too close to the elongated bolt hole.

I did not take pictures of my Hall intake but it appears that there is a variation in either the casting or the machining of the gasket surfaces.

I'll look through my pictures and see if I can find anything that will confirm or deny that thought?

BUT my thought is that it is the gaskets themselves. The Print-o-seal blue ring thing on those gaskets is not working for your set up at all.

This is a better fitting gasket. Simple and straight forward. Consistently nice and flat.

You have the gaskets on upside down. Flip them over and the holes will line up.

Yep, you are correct.  I am going to dry install a set of the Tim Meyer gaskets and pressure test with 20 PSI.

The first photo is an old Felpro gasket.  The second is a new Tim Meyer gasket.

Steve, I am still concerned you are putting too much pressure on the sealing surface at 20 psi.  The design isn't purposed for that.

@panterapatt posted:

Steve, I am still concerned you are putting too much pressure on the sealing surface at 20 psi.  The design isn't purposed for that.

I agree but frankly can't answer that question about what pressure they will hold?

Certainly in a blown induction, they need to hold more, the entire pressure of the supercharger.

I've never built that configuration and have never heard it discussed before.

I'm learning here about it but this has to be a gasket material composition issue but in disassembly I'd be looking for cracked portions at the thinnest points to confirm.

Thinking about head gaskets, they are all now reinforced with some amount of sheet metal. I'm not old enough to swear that there was a point in which they were not?

I do remember the pure copper sheet head gaskets for the supercharged drag engines. It is softer but more compressible.

I will test with 10 PSI initially.

Holding negative pressure or positive pressure should be the same.   17 in mercury is 8 PSI.  I would start there

I dry Installed the Tim Meyer gaskets and tested with low PSI (8 or 10), and the same problem happened right away.  It holds pressure and gradually leaks it out.   My plan is to disassemble and reinstall with sealant.  Here is a photo that shows some of the soapy bubbles.

My GT500 runs at 15 pounds boost if that means anything. Top fuel dragsters run over 40 pounds.

Do you use sealant on your intake gaskets?

No but I also do not use printoseal gaskets anymore as they seem to become printoleaks.

Is it only that one spot? The leak/s are located over the top of the intake ports?

Was there any porting done on the heads?

Each of the ports leaked. Some more than others. The leaks are at the top of the port. My hunch is there are leaks at the bottom of the ports because I think I can hear them.

there does not appear to be any porting work on the runners. They look factory.

When you disassemble again, put a straight edge along the top of the ports where the leaks appear to stem from.

At this point it really sounds like the heads may be warped but seems so unlikely since that is something everyone would have noticed during head prep?

If the sealing surface is warped, those could be resurfaced without disassembling the heads.

It is more common to find that the exhaust side is warped and needs resurfacing.

I should also mention that there should be no pitting on the gasket surfaces and even if you don't see any, you shouldn't be able to catch a finger nail on any of the machined surfaces.

Shops are often leary to resurface any heads these days in fear of being accused of over cutting them and ruining them?

I have seen surfaces that were still pitted after resurfacing and the machining marks kind of disguised the pits.

It is strange to mention all of these things but this is a VERY unusual situation and something non imaginary is causing it.

I tested again and the gaskets leaked as usual.  I was able to reduce the leaks to almost nothing by applying additional torque to the bolts.  Upon disassembly I noticed something interesting. As you can see in the photo, there is no manifold imprint on the bottom of the gasket on one side.  It looks like the manifold is only in contact with the top of the cylinder head on that side.

Steve,

If you haven't done this already, try placing the manifold on the block without any gaskets or bolts and check to see if the head and manifold gasket surfaces are parallel (top to bottom).  If necessary, slide the manifold toward one head to lessen the gap and hand thread a couple of bolts for alignment...repeat for the other head.

You might be able to get better sealing by using  0.125" intake gaskets.

John

Your leaks were along the top, not the bottom. Try a thicker gasket or just double them up.

Thanks you guys.  I ordered a couple of sets of the .125 gaskets.

In the above photo, the stuff you see at the top is soapy water from the spray bottle.  It puddles on top of the manifold and soaks down especially during disassembly.  I have consistently heard compressed air escaping out from under the manifold, even when I get a seal at the top with Right Stuff or a bunch of torque.

Also, I am fortunate to have found this problem now when the engine is on the ground and easy to work on.  Finding it later when the car is driving and blowing blue smoke from the exhaust would be more difficult to fix.

Thank you all for your help with this.

It is very strange to find an intake machined that much out of whack. It is something normally no one ever looks for.

It does appear that a thicker gasket SHOULD compensate but you may need someone with a mill to re-cut it.

If Gary was still around this would never have happened. Someone screwed up over there.

Maybe you could interest Marlin to fix it for you? It should be cooling down over there at the shop by now. 110° in the shade can make you a little crazy?

The trapezoid on the engine could be out of square.  Maybe the deck on the block is milled more on one side.  Or one of the heads is milled more than the other.

One of the decks or heads could’ve gotten milled  at a slight angle.