How much should I mill my 1916 stock head to bring the compression ratio up to 5 1/2 to 1 ? Thanx for the info.
The maximum safe cut is 1/8" (from what I've read here) on an uncut head. Removing 1/8" from your '16's 4.1:1 compression ratio head will only up the compression ratio to 4.67:1 according to my calculations.
I've seen heads milled .200 but it may depend on the head how much you can go. While a milled low head will bring up compression it really doesn't compare with an aftermarket aluminum head. It may also get pricey to mill that far if you have to pay machine shop time. Many shops will want the bulk removed on a mill before it goes on the surfacer, more labor.
How can you tell if your head has been milled can you measure from headgasket side to topside of head near a head bolt hole if so what would be measurment on a low head & high head be and at witch bolt would you measure. thanks Ross
If you look at the thickness of the head "deck" at the centre water passage you will get a idea of how thick it is there. Most high heads seem to be about 3/16" there as found. I have found a very few that were more like 9/32" there. They seemed to all be 1917 ones. These can obviously have more milled off. I have heard of guys milling these 3/16" maybe more. On the Montana 500 you are not allowed to run a aftermarket head so I here guys search out these odd '17 heads to mill.
I have not studied the low head so can not comment there.