The first 2 years of the 318 (before the 340 came out) had high compression as well. Had a few people argue with me but when I pulled my original '68 out of my Coronet I was shocked that the pistons were only 0.030 in the hole and the measurements put it at about 9.2:1. If you look at the factory manual for '68/'69 they claim 9.2:1 or so as well. After the 340 came out my theory is the purposefully dropped the compression to make a large difference between the 340 and 318 in the brochure.
