# Differences in head gaskets



## robertsj (Dec 21, 2018)

I have a 68 lemans with a 1976 455 with 6H heads. I've removed the drivers side head and am looking at new head gaskets. Why is there such a big difference in price? I see Mahle gaskets for $19 and Cometic $303. It is pretty much stock and I don't plan to add more. It's a nice cruiser with enough of torque. So is there a reason for such a big price difference? Thanks!


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## O52 (Jan 27, 2019)

Cometics are about as good as it gets. Normally used for high compression builds and / or to meet quench or compression goals. Requires special block preparation and can be ordered in various thickness's. Price varies with the thickness. 

Best general head gaskets are Felpro. They run about $30 each. The thinner .039 version about $45.


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## PontiacJim (Dec 29, 2012)

The Felpro head gaskets are a "standard" that most use. Never had an issue with them, and generally neither does anyone else.

I went with Cometics for my 455 build. Not inexpensive as they were $100 each, but I got them thin at .027" so as to get a good "squish" area between my piston crowns and head surface.

The Cometic head gaskets are called MLS, or *M*ulti-*L*ayer *S*teel. It is a sandwich of steel and viton rubber. The advantage from what I read, is they work well with aluminum heads where you get movement from the differences in heat expansion rates of the aluminum head and cast iron block.
"Smoothness has become a major issue with bimetal engines because the difference in thermal expansion rates between an aluminum head and cast iron block creates a tremendous amount of sideways shearing force and scrubbing action on the head gasket. If the surface finish is too rough (more than about 60 RA), the metal will bite into the gasket and pull it sideways as the head expands and contracts. The cumulative effect over time can cause a delaminating effect in the gasket, literally tearing it apart causing it to leak and fail."

They are also recommended for boost applications. And of course, work well with iron blocks/heads.

The other advantage is that you can get them in a big variety of thicknesses, or even custom, so this can in affect alter compression or "squish area" between the piston crown and head.

They say that the block/head require a smooth finish, more so than what is typically given when the block or heads are milled by most machine shops. Cometic recommends a surface finish of 50 RA (roughness average) or finer. By comparison, Fel-Pro recommends a finish of *60 to 80 Ra for cast iron cylinder heads* and blocks, and 50 to 60 Ra for aluminum. However, many also say no issues without the smoother finish - but it may also depend on your machine shop and their type of equipment and techniques.

You can read a thorough explanation about all this here:



Cylinder Head Resurfacing


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## BearGFR (Aug 25, 2008)

There is a subtle difference between the FelPro and the Mahle gaskets that happens to matter on my engine with the professionally ported heads I run. The Felpro gaskets have two long, canted, oval shaped holes near the top edges while the Mahle's (formerly Victor Reinz) gaskets have regular round holes there. Because of the way my heads have been ported, if I use gaskets that have those long oval shaped holes at the top it will suck oil through them into the intake ports.

Bear


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## robertsj (Dec 21, 2018)

Thanks so much for the replies! I am sticking with the cast iron heads for now (with low compression ratio). Is it possible that I have the original head gaskets on there now? I only removed the drivers side and it was a metal gasket. Here is a picture of the one i took off.









From what PontiacJim says I should not have issues with thermo expansion. Sounds like the FelPro should be ok for me.


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## PontiacJim (Dec 29, 2012)

robertsj said:


> Thanks so much for the replies! I am sticking with the cast iron heads for now (with low compression ratio). Is it possible that I have the original head gaskets on there now? I only removed the drivers side and it was a metal gasket. Here is a picture of the one i took off.
> View attachment 146748
> 
> 
> From what PontiacJim says I should not have issues with thermo expansion. Sounds like the FelPro should be ok for me.



Those are most likely the stock head gaskets. Keep it so you can compare the new Felpro head gaskets - should be all you need.


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## robertsj (Dec 21, 2018)

Thanks PontiacJim!


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