I found a compression calculator on line and entered all the known variables in and this is what I came up with.

The difference in compression between a 3.810 bore and a 3.910 bore on a 0.040 gasket thickness appears to be about .05 difference in compression.

3.810 = 9.70
3.910 = 9.65

8 = number of cylinders
3.780 = bore
3.622 = stroke
8 cc = dish in the LM7 5.3L piston
.040 = gasket thickness
.006 Piston out of the hole measurement
60 cc = 243 heads milled .030



known variables with 3.810 bore



known variables with 3.910 bore

If you go down to 58cc with the same gaskets thickness and bore size difference. This would need to be roughly .042 milled but would need to be verified. It's typically .006 of removal is around 1 cc on these heads.

3.810 = 9.93
3.910 = 9.88



known variables with 3.810 bore



known variables with 3.910 bore

 

That's some good info. I read through most all of the threads on running a .040 gasket on here, but none of them addressed the over bore so that's why I asked. The over bore of the 3.910 doesn't really affect the compression. Knowing that I might have just order the C5788-040, but it was out of stock so either way they would have to cut new ones. Thanks again for the compression numbers thats great info.

 

I am not sure what you are trying to achieve but I thought it might be helpful for you to understand the effects of what you are doing.

Sorry! I needed all 3 of the gaskets summit had. I am not sure if any one else stock's that size.