1G Head Gasket Thickness

[Slahm]

OK, I have my enginge at a machine shop, and they want me to choose a head gasket thickness. ?!?

I would have assumed that since they are stroking my 4G63 - 40 over, with an eagle kit, and they are doing ALL the prep to the block and head, that they could make this decision, but it seems like they want me to.

There has never been much taken off the head until now, it was cleaned up once, but very lightly.

Any suggestions as to thickness? I suppose a thick cometic would be good, to reduce the compression a bit, this is a rally build, and I want quick spool. But how thick? How would I normally determine the correct thickness? And is adding a bit to reduce the compression a viable idea?

Shops! I really think they should have some idea here, but don't want to piss them off by saying that any more...

Thanks!

 

[Calan]

The problem you are going to have is that if you go with an MLS gasket, the .040" over-bore is going to limit your selection as to what is available. As far as I know, about the only name-brand manufacturer that offers various thickness in different bore sizes is Cometic...and opinions vary greatly on the quality of Cometic head gaskets. Of course this assumes the machine shop is putting the proper surface on the head and block for an MLS gasket in the first place.

If the head hasn't been shaved to some ridiculous amount (i.e. past the service limit), you should be able to run the Felpro Permatorque MLS if you want, which is proven to hold up to some high power with the right head studs and surface prep.

A search on "head gasket" at extremepsi will probably give you the most common (and best) options available.

 

[Slahm]

I will look there, thanks.

To add to the confusion, they are talking about quench time, whatever that is, and too much turbulence if I go with too thick a gasket!

Great fun!!

 

[My1GLaser]

I've heard of "quench pad" and not having enough turbulence if the gasket is too thick. You want turbulence and a violent swirling action to reduce hot spots in the CC. I am not an engine builder by an stretch! I just did a lot of reading when I built my motor.

From what I understand, the quench pad is determined by the distance from the bottom of the head to the top of the piston at TDC. Lets say your pistons come right up to the top of the deck surface, and your HG is .055" thick. Then you have a .055" quench pad.

Mine are about .007" above the top of the deck surface and I am running the .055" Felpro Permatorque MLS HG. So my quench pad is .048"

From the research I did when I built my engine, you don't want it less than .035" or greater than .060". Our pistons are dished, so the actual effectiveness of the quench is much less than flat top or dome pistons since the outer ring of the piston is the only area that close at TDC.

 

[Slahm]

Thanks, they seem to have figured it out! He worked the numbers for good quench, or so he tells me!

 

[oh-b-1g]

The problem you are going to have is that if you go with an MLS gasket, the .040" over-bore is going to limit your selection as to what is available. As far as I know, about the only name-brand manufacturer that offers various thickness in different bore sizes is Cometic...and opinions vary greatly on the quality of Cometic head gaskets. Of course this assumes the machine shop is putting the proper surface on the head and block for an MLS gasket in the first place.

If the head hasn't been shaved to some ridiculous amount (i.e. past the service limit), you should be able to run the Felpro Permatorque MLS if you want, which is proven to hold up to some high power with the right head studs and surface prep.

A search on "head gasket" at extremepsi will probably give you the most common (and best) options available.

What were you talking about when you said "putting the proper surface on the head and block" to use an MLS gasket? Building my first complete 4g63 and hadn't heard of that.

 

[WES_393]

What were you talking about when you said "putting the proper surface on the head and block" to use an MLS gasket? Building my first complete 4g63 and hadn't heard of that.

MLS gaskets can't fill surface imperfections as well as Composite gaskets can. Any flaws will leave gaps between the mating surfaces and the gasket. These gaps are a weak point in the seal and often allow pressure to push past the gasket.

In order to avoid this, the mating surfaces of the head and block must be machined to a surface finish smooth enough for the MLS gasket to seal. Smooth enough to nearly see your reflection.

 

[oh-b-1g]

Thanks. Don't suppose ill need to run an MLS gasket, but I was curious.