cast iron ex. manifolds and alu heads.

[Calypso]

Gasket or thin bead of hi temp silicone?

[Scotthatch]

How flat is the manifold?

[cjperformance]

Gasket or thin bead of hi temp silicone?

If available a steel shim gasket is best in this scenario, with no sealer to allow for expansion differences.

[cv67]

Gaskets are cheap esp the stock type if it covers the port. Under 10 bux and last forever

[Geoff2]

I would not use a steel gasket with alum, dissimilar metal corrosion. I have successfully used high temp silicon many times, no issues. The manifold does need to be flat/straight if using sil.

[mag2555]

The head even though it is Aluminum likley expands a tad slower then the iron Exh Manifold , so I would use a Copper gasket that you have red siliconed to the head and just let the Manifold float on the gasket with no sealer.
Going back over the bolts after the fist 3 to 4 heat up and cool down sessions will be needed.

[user-23911]

I would not use a steel gasket with alum, dissimilar metal corrosion. I have successfully used high temp silicon many times, no issues. The manifold does need to be flat/straight if using sil.

There's plenty of OEM situations which use multi layer steel shim gaskets with cast iron manifolds and aluminium heads. They last for years.

[cv67]

most new cars do this, I dont see a problem.

[PackardV8]

My machinist, who's built a thousand long block SBCs, always removes the exhaust manifold gaskets from the remainder of the gasket set he gives to customers.

One customer, not finding the exhaust gaskets, went to NAPA, bought a set and then came back some months later with a leaking manifold.

[Abbottracingheads]

Check with Flatout gaskets. They make a MLS header gskt that is badass.

[Walter R. Malik]

Pure soft copper ... or, O.E.M. type MLS.

Be sure there is nothing there which would act as a heat barrier.

[cjperformance]

I would not use a steel gasket with alum, dissimilar metal corrosion. I have successfully used high temp silicon many times, no issues. The manifold does need to be flat/straight if using sil.

There's plenty of OEM situations which use multi layer steel shim gaskets with cast iron manifolds and aluminium heads. They last for years.

Exactly

[GerryP]

I don't use anything between the iron exhaust manifold and the aluminum head. If the flanges are flat and clean, I just bolt on the manifold. So, given that, what doom am I inviting upon myself?

[cjperformance]

I don't use anything between the iron exhaust manifold and the aluminum head. If the flanges are flat and clean, I just bolt on the manifold. So, given that, what doom am I inviting upon myself?

Your curtains will fade and your crops will die !

[Newold1]

Calypso

When you ask a question like this it would always be helpful if you identify the year and make of engine, it is important!

If this engine is a late model type, GM, Ford, Mopar. most imports all use and sell MLS type stainless exhaust flange to head gaskets that are fairly inexpensive and will out last the engine in most cases. I for one use them with aftermarket headers and they are also available from Cometic and other aftermarket gasket makers.

Dump the use of gaskets sealers and silicone, etc. that's a low tech way of sealing exhaust flanges to heads in almost all cases. Please come to now the future!