Aluminum head thickness.

[hudson1948]

Does anyone know what is the most you can mill a 308 aluminum head without the valves hitting?

[Ken U-Tx]

Nominal head thickness was 2.000" Maximum milling was .060", or 1.940" thick. At .060" you often find that the exhaust valve hammers the sparkplug electrode gap shut, especially with either 309742 or 311040 cams due to their higher lift. This can sometimes be gotten around by putting an extra plug washer on the plug, but with.060" off an aluminum head, you might find it pings under load too.

[dougson]

Nominal head thickness was 2.000" Maximum milling was .060", or 1.940" thick. At .060" you often find that the exhaust valve hammers the sparkplug electrode gap shut, especially with either 309742 or 311040 cams due to their higher lift. This can sometimes be gotten around by putting an extra plug washer on the plug, but with.060" off an aluminum head, you might find it pings under load too.

Just curious, what would be the compression ratio of a .060 milled head?

[Hudson308]

Nominal head thickness was 2.000" Maximum milling was .060", or 1.940" thick. At .060" you often find that the exhaust valve hammers the sparkplug electrode gap shut, especially with either 309742 or 311040 cams due to their higher lift. This can sometimes be gotten around by putting an extra plug washer on the plug, but with.060" off an aluminum head, you might find it pings under load too.

Ken's info is dead on in my experience. I've had the spark plug problem on a head milled .080" with a stock ('52) camshaft. Randy Maas probably knows the answer to your compression question better than anyone, but my guess is that compression is just over 8:1 with a stock gasket and the head milled .060". This is enough to cause pinging with too much timing advance or poor fuel, or if your fuel mixture is running a bit "skinny" for some reason. I've now got a .060" shaved aluminum head on a '52 308, running flat top pistons and a bit more cam than stock. Timing is about "halfway" on the factory flywheel marks, and I don't have any ping problems. I try to use mid-grade unleaded fuel with a bit of CD2 added to each tankful. No mountains here in Minnesota, though.

[dougson]

[...... I've now got a .060" shaved aluminum head on a '52 308, running flat top pistons and a bit more cam than stock. Timing is about "halfway" on the factory flywheel marks, and I don't have any ping problems. .[/QUOTE]

I love it, "halfway" on the factory flywheel marks :D, Try this on a '09 ZO6!