The heads made it back this week. I spent all day yesterday double checking all measurements. Since I knew the ACR's only open .020", I removed the additional shim that was added to ensure the chambers would be as small as possible. I cc'd the heads (about 5 times) and was disappointed in what I found. The front head is 94.5cc's and the rear head is at 94cc's. I asked to the heads to be at 93cc's for the 11.0:1 and Scott said he would bump that to 11.2:1, so I was expecting to find sub 93cc chambers. Just to make sure I wasn't missing anything, I went back and made a mold of the piston crown. I cut off the valve reliefs and cc'd the mold. I cc'd the reliefs on the piston and subtracted the two. Again, I found my self disappointed as the total cc's on the piston dome volume as they were only 10.5 cc's instead of the 11.5 that I read on the board. After that, I checked my deck height of the pistons. I found the rear sitting in the hole .0065" and the front in the hole .0035". The top of the piston above the ring land measured 3.968" and it was .172" to the top of the ring land. Lastly, my .027" Cometic gasket had a bore of 4.034". When you factor all that together, my compression is as follows:
Front Cylinder Static - 10.91:1
Front Cylinder Dynamic - 9.45:1 (calculated @ .053" lift....so not true dynamic compression)
Rear Cylinder Static - 10.89:1
Rear Cylinder Dynamic - 9.44:1 (calculated @ .053" lift....so not true dynamic compression)
I was wanting the compression up there at 11.2:1 (about 9.65-9.7 dynamic compression), so now I'm left with a decision. I can throw everything together, have the heads milled more to get the chambers where they need to be, or buy a -4 degree cam gear to get my dynamic compression back to the 9.65:1 that I had planned the build for.
Does anyone have any thoughts or suggestions on which direction they would recommend?