[Fot] How far can a GT6 head be milled?

[Scott Janzen]

The answer is it depends on the head casting, as the mfg process is not that precise. 

The head on the engine in my car appears to be 3.17" - hard to get a perfect measurement installed - and it was calculated at 12:1 compression with 0.030" overbore.

I'm building another engine, where the head was milled to 3.220" and it wasn't safe to go any further.  There's a thin spot in that head, below the #1 exhaust port, about midway between the combustion chamber and the edge of the head - you can see the metal starting to lift up from the milling process, over the coolant passage.  That head ended up at 11.4:1 compression with a 0.030" over-bore.

A good machinist will take shallow passes and look for imperfections.


On Jun 29, 2014, at 4:07 PM, Jason Sukey wrote:

I'm getting ready to mill the head on my GT6 for a bump in compression.  I
currently measure 3.255" thickness, my math shows that I want to end up at
3.215" when I'm done.  I can't find much info on how far people are safely
milling the GT6 version of this head, only TR6 info.  Does anyone have
experience on this?  Is there enough meat in the casting to remove this
much material without hitting water?

Thanks,

Jason Sukey
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