Aluminum heads on an iron block & head gasket question

Imo Apita

Imo Apita

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Feb 28, 2009
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Planning on aluminum heads on my (hopefully) soon to build 383.
Found a post on CF that has me scratching my head.

The surface needs to allow the aluminum head to move/slide around as it expands and contracts faster than the steel block. Both pieces are moving at different rate as they heat up (and down). Zero deck or +0.025 stock deck has nothing to do with this. It's the finish on the deck and head that will allow the aluminum head to move rather than tear the gasket (or what ever happens at the micro level). Again, the block and aluminum head should have an Ra of 20-50 while an iron head to iron block should be 60-120 Ra. At least thats what the professional machinists write and i just looked it up again but i'm not even a machinist so take it for what its worth
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Never heard of this being an issue.
The fact that I've never heard of it doesn't mean that much so is there any merit in the above statement?
I know of the different expansion and contraction rates but is it really something to be concerned about?
Just ignore and go with the head gasket the head guy recommends?
Curious minds would like to know.
 
I bought some thin metal head gaskets (rubber coated copper) from Summit and, when I got them, it said on the packaging that they should not be used with alum/iron. Don't know why, but I replaced them with Fel-pro composition type that were a little thicker but OK for alum/iron.
 
Use composition gaskets. Having the surfaces of both the heads and the block 100% flat and parallel is a longshot, and the expansion rates of both being different, the steel shim gaskets won't live too long.

Using composition gaskets gives everything more room to flex and will cover any surface differences.
That and the fact you can change your compression a little by just using a thicker gasket makes a winner. But don't forget to watch the quench distance too. Get too much and detonation can be a factor.
 
Good point. Quench distance is what I was looking for with the thinner rubber/copper gaskets but the Fel-pro composites were only .008 thicker.
 
Thanks for the replies, essentially nothing to worry about with a Felpro.
Also read that a 383 will wear your tires out faster then a 350....should I be worried again.....:lol:
 
Well, you should not believe all that is written on CF..... :lol:

Aluminium on iron is no problem when you are using propper coolant with inhibitors. Most head gaskets will be ok unless the instructions from the supplier say otherwise.

Arne
 
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