I would agree that the 67 318 "should" have the highest compression, except for one thing!! The one important thing that also impacts compression is "piston height". If you look at the chart I posted (post number 11), it shows that the 67 318 had a piston height of 1.75. The 69 318 has a piston height of 1.77. Now someone will have to do the math to determine what compression each motor would have with the correct CCs for each head in each year???? I remember seeing a chart of compression ratios on these motors and if my memory is correct the 67/68/69 318 came with 9.2:1 compression.