my 71 454 has 113cc oval open port heads, 820's
it was rebuilt and the builder used forged flat top pistons. what should my compression be? he said he thought around 10 to 1

 

 

Here is a link:
Motor Size and Compression Calculator

Plug in your numbers, have fun.

 

If I have a flat top piston, doesn't it really have a negative cc number due to the valve reliefs, as opposed to being 0? And if my gasket is 0.039 with the engine being zero decked, I use 0.039 for my gasket thickness,right? Sorry for the stupid questions, I plugged in my numbers, and got a CR much higher than what my engine builder told me.
I have :
4.155 bore
3.750 stroke
8 cylinders
70 cc heads
flat top pistons
0.039 gasket

which gives me a CR of 11.6:1 while my builder told me it was more like 10.75:1.