The 1968 289 heads were 60CC NOMINAL rated. That really means they were bigger than that and could still be that size after milling. Actual heads that are measured will be around 62 CC unmilled. This applies to castings marked C8AF-AK, C8AF-SM and C8ZF-G.
Original compression ratio was stated as 8.7 to 1. Again this is a nominal rating, the pistons sit about .040" in the hole at TDC while the CR was calculated at zero deck.
You need a pretty mild cam to avoid killing all bottom end power.
I'm having a hard time finding time to work on the old cat right now, but I will get the numbers as soon as possible, its crucial that i know my compression, the cam the guy before put in it requires at least 9.5:1 and i don't think i'm anywhere near that.
I don't have a copy of the book Bill is referring to but that sounds like a reasonable number for a '68 head in original unmilled form. Figure 8.5 to one compression as a real world number for cam selection.
"its crucial that i know my compression, the cam the guy before put in it requires at least 9.5:1 and i don't think i'm anywhere near that."
True. Compression can compensate for valve overlap on a cam. If you are stuck with the cam already in the car and don't want to change it, then you could always go with an earlier set of 289 heads with the 54.5 cc chambers to bump it up a bit.
Hipo and 2v heads have the same size valves and ports, so you could nab a set at a swap meet. that's the easy fix. assuming theres a big enough problem to warrant changing the heads.
I have established that the heads are off of a 66 289. the car is bored 30 over and aparently the pistons are 8.5:1. And something definetly needs to be done. The car has absolutley nothing until about 40mph...... I need help!!!!!!!