[Snipe656]

If you do mill the heads just do it for trueness and not for large increases in compression. The GT40 heads did not have an overly thick deck. One set that I had was milled down for more compression and I battled sealing issues on two different short blocks with those.

As far as compression my first 306 that I used GT40 heads was built for around 10.5:1. That engine would sometimes ping or I should say always did pre detonation if I filled up at one specific brand station. I personally would stick around 10:1


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