Cylinder Head Hardness

[Cameron Morison]

Hi DSMers

Im looking at building up a new cylinder head for my 4g63 mirage/colt/proton, its currently just over 600hp but the cylinder head is stock porting other than just a slight tidy up with a sanding barrel to remove casting marks.

Is there any data on cylinder head hardness at all, what is 'new' or good, then what is acceptable also and at what point the head should be scrapped or just demoted to a low HP level. It seems to be something that there is not much information on.

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[1990TSIAWDTALON]

There are 3 service limit tabs on the deck side of the head. If you mill down to those, there is nothing left to mill and that head will need replaced if/when it gets to that point.
Aluminum is just that, soft metal. Here is a hardness test, maybe it will be of some help.
Marty

 

[jed344]

I am not aware of a way to test it, But i have seen data over the years showing virgin heads with less miles on them seem to hold head gaskets better. I have used heads that were decked to the indicators before. Last head was 5.185 as i recall witch is considered service limit but figuring in piston protrusion and head gasket thickness used it should be fine for the goals of that motor.

 

[donniekak]

I have noticed that the aluminum seems to anneal over the years, especially at high power.
We used a few new oem heads that held up better at high boost.

 

[Cameron Morison]

Just got the head back from hardness testing. It came back at low 70s on the Brinell scale which is pretty poor. Ill keep looking for another casting that hopefully hasn't been hot. I know this one has been hot, but never knew how hot. It would be fine to use on something that didn't require extra clamping but not a good starting point for a high horsepower head.

Been talking to a few engine builders. Anything north of 90 is a good one, ideally north of 100. New heads, or very close to tend to be up towards 110. Apparently 70 is within spec, but obviously that's for an OEM application

 

[Mello]

Get a hold of a heat treater & have re-tempered.

 

[Cameron Morison]

Get a hold of a heat treater & have re-tempered.

Been a while.. sorry late reply

regarding retempering heads, I am aware of a local company that can do it. However what I am not sure of is what level of distortion is likely to occur.

Im certainly not going to be throwing out or destroying any heads just in case.
At the moment I have the one on the car (mid range hardness), the softer spare, and a spare that came out mid-good on the relative hardness.

If it was an OHV head without cams in it then retempering would be a no-brainer but with cam bearing alignment being so critical it makes me nervous to get one retempered. Im not sure how much a head can be straightened afterwards if it did bend.