Exhaust manifolds

[bkmech]

I understand 390s have a lot of exhaust manifold problems, mine sure does I'm taking them off once more and having the planed off. Is a felpro gasket OK or do you recommend a certain brand that will last?

[simplyconnected]

Welcome to Squarebird.org, Jeff.

Your engine came from the factory with NO exhaust manifold gaskets at the heads. I suggest you take your manifolds to a good machine shop and have them shaved flat. Install them with no gasket. BTW, 390 exhaust manifolds are made of the exact same iron all the rest are made with. After 50-60 years of heat/cool cycles, many thousands of times, any manifold might give out.

All exhaust gaskets are softer than cast iron and they tend to blow through and leak. Understand that when manifolds are new they are not 'seasoned' so they tend to warp. Gaskets are a very temporary fix. - Dave

[DKheld]

I have the original engine from my '60 Tbird. Never had a problem with the exhaust manifolds in 54 years. The rear main seal is another story.....

Was going to rebuild my engine but found a rebuilt one cheaper than I could buy the kit to rebuild mine so just installed it and put my original engine (with the original manifolds) in the back of the garage for "one of these days".

The rebuilt engine I found did not come with manifolds and rather than risk warping or damaging the originals - I bought a used set of originals. Didn't have them professionally shaved - just cleaned and filed them then installed with Fel-Pro gaskets, new bolts, washers and locks - lasted about 1K miles and then blew out.



Took the manifolds back off and had a machine shop surface them.



Re-installed without gaskets as original. Good so far at about 1K miles.


Eric

[Joe Johnston]

My 63 uses a thin metal heat shield between the manifold and block, no gasket. Heads were rebuilt, manifolds machined true and a very liberal coating of anti-sieze was used on everything. The machine shop also told me to follow the torque values and sequence in the manual and NEVER try to tighten a cast manifold to stop a leak. They HAVE to be flat and mate perfectly to the head, just like when the engine was new. If over-tightening doesn't crack the manifold, not allowing it to expand and contract (which is the reason for some elongated holes) will. 3 years & still A-OK with no gaskets.

[simplyconnected]

...The machine shop also told me to follow the torque values and sequence in the manual and NEVER try to tighten a cast manifold to stop a leak...

Yeah, that's how all those manifold 'ears' get broken off.

Cast iron is amazing stuff. By definition, cast iron is 2% carbon with NO grain structure because it's poured into a mold, not formed into a shape. After the pour, cast iron shrinks one inch per linear foot. Think about that because your heads are over a foot long. They also get cherry red hot on long trips, so you know lots of motion is going on.

Let's discuss bolts. I use 3/8" Stainless Steel Socket Head Cap Screws (SHCS). They have no carbon in them so they do not flake off or shrink in size. I can use an Allen wrench or grab them with Channellocks around the head. I suggest using them for your exhaust manifolds.

If a bolt breaks, extracting is not a big deal unless the bolt was bottomed out. So, never put bolts in that bottom. I'd rather see the hole tapped all the way through. - Dave