not 100% sure, but i thought .030

 

I think he means like -3 or -4 cc's. But he's looking for an exact number. I suppose you could measure the dimensions of each notch and calculate it (probably more accurate than cc'ing it). It would take some decently fancy geometry, though. Post up the measurements, and someone here will take the time to figure it out (if they don't, I will).

For example - let's say the diameter of the notch is 2" (I know it's not, but just an example). That gives you an area of 3.14" sq (pie are square and all that - no, pie are round! lol. I kill me.) Or perhaps it's better to think of a section of a sphere - running the numbers for a 2" cut, .2" deep, I get 2.18 cc. I'm probably wrong. But look at my reference:

Sphere - Wikipedia, the free encyclopedia

What the hell do I know?

 

Just get a medicine dropper from rite aid and fill it with water. Add one drop at a time to the piston relief and see how many mills to fill it up.

Of course this only works if you can get to a piston, if it is in the engine then you can't do that. I would look on summit or Jegs for a stock rebuild kit (specify your year), and see what pistons they put in the kit, and then grab the information for that. I did a stock rebuild kit for my 1979 351w, and the pistons that came in it were 12cc of dish + valve relief. Conversely if you pick a stock style rebuild kit for a 1969 351w, it gives you pistons that have a 4cc dish.

 

Its easier to use a syringe from tractor supply with cc's already marked off on it...

Even if the pistons are int he block you can still measure them. Just tape them off by laying the tape flat across the piston. This will leave a hole under them, make sure the tape is stuck down tight against the tops of the pistons. You will probably have to clean them off to get good adhesion. I would use the blue painters tape or masking tape, something easy to get off after your done.

Once taped off, fill your syringe with oil. Make a small hole in the tape over the valve relief, you want the hole at the highest part of the relief so you can fill the chamber full with oil. Then start adding oil and keep track of how much your adding by reading the cc's your injecting till the valve relief is full.

 

The difference in compression between -3 and -4 ccs is .12. So the difference between 9.69:1 and 9.57:1 is "it doesn't matter".