I've just had the stock L28 out of my '76 280Z rebuilt. It had to get punched out by 30 thou, and the dished pistons were discarded in favor of flat-tops. Can anyone tell me what the CC's on the stock pistons would have been, or even just tell me what my new displacement and compression ratio should be? I guess I'm also going to have to figure out what kind of timing to run with the new compression ratio. I was using premium fuel before, and now I'm going to need it for sure.

The piston dish will not alter your displacement. Your displacement is the (new bore area) x (the piston stroke) x 6

Compression has changed. You can calculate all of it here:

http://www.atlanticz.ca/zclub/techtips/calcs/engine%20builder/index.html

Stock was 86mm bore and 79mm stroke. This gave 2753cc displacement.

You now have a bore of 86.75mm. Running it through the calculator gives me a new displacement of 2802cc.

As for the compression, what head, and has it been shaved at all?

Thanks for the replies. It's a stock N42 head, stock height Fel-Pro gasket. I didn't realize the dish of the piston would not factor into overall displacement.

Here's what the calculator spat out, after I added the overbore:

Block Height= 207.87 mm

Deck Height= -0.07 mm

Chamber Volume= 44.6 cc

Cylinder Volume= 458.9 cc

Gasket Volume= 7.86 cc

Dish Volume= 0 cc

Deck Volume= 0.41 cc

Uncompressed Volume= 511.35 cc

Compressed Volume= 52.87 cc

Compression ratio= 9.67:1

Total displacement= 2753.37 cc

A different calculator I found today gave me a compression ratio of 9.975:1... may as well say 10:1. Have to be a little careful with the fuel and the timing I think. The bottom end looks stout enough, anyway, and I put in the good ARP fasteners with the rebuild.

Now can anyone tell me what the new HP should be?