It's usually always a lot lower than what you are hoping for with a stock type bottom end. Looks like the stock 7cc dish type piston, probably about .050 below deck on average on a good day, sometimes .080 (or farther!) under deck, and the chambers are usually the maximum volume as minimum and usually even larger... For example, I'm going to assume stock head gaskets with pistons and a .043 head gasket, 75 cc chambers, and pistons .040 under deck, we come up with a booming 8.4 to C.R., which will coincide pretty well with your usage 87 octane fuel. Probably accurate to 1/2 a point. If you haven't already, run a compression test and at least get a map of your cylinder pressures. Probably the quickest way to a lower ET is headers with low restriction exhaust (if you don't already have them) and deeper gears, if you can live with them on the street. Be sure to baseline your car before doing anything, though.
