I have to respectfully disagree. I think there are too many errors there. Wrong. The E31's came on all 69, 70 and 71 240Z's in North America. That would mean that there were about 46,000 Z's equipped with the E31. They were used for racing by BSR and BRE in 70/71, but both switched to the E88 heads when they came out. The E-88's had better flow through the intake/exhaust ports, and a slight milling brought the compression back up. The E88's also had better castings, as the E31's tended to crack around the exhaust valves. 42.4 cc combustion chambers, with 42mm intake and 33mm exhaust valves. Wrong - There are at least four different heads that carry the E88 casting number. 1. The E88's started showing up on the last of the Series II 240Z's. Although carrying the E88 casting numbers, they still had the smaller combustion chambers of the previous E31's ie. 42.4 cc 2. The E88's that were standard on the 1972 Model Year or Series III 240-Z's. These had the same combustion chamber design as the E31 and early E88's... only increased to 44.7cc 3. The E88's that were standard on the 1973 Model Year or Series IV 240-Z's. These were emissions heads. The combustion chamber design was changed to improve emissions control, and the size was increased to 47.8cc. This is not a good performance head.. and it is difficult to rework to make it good. 4. The E88's that were standard on the 1974 Model Year 260Z. These were the same combustion chamber as the 73's but with a larger 35mm exhaust valve. I believe that these are better references: http://ZHome.com/ZCMnL/tech/128combo.html and http://ZHome.com/ZCMnL/tech/head.htm and http://ZHome.com/ZCMnL/tech/E31andE88Heads.htm FWIW, Carl B.