[wh33lman]

How does one measure a domed piston in order to determine compression ratio?
They have been shaved down to lower compression at one time, so factory numbers do not apply.
Best I can tell, by using a straight edge and feeler gauge, is this is a .013" dome, but do I determine the volume?

[25stevem]

First Get some clay.
Crank the piston 1/4" down the Bore.
Oil up the piston top and the Bore.

Mold the clay over the top of the piston and dome.

Peel it off carefully and then CC that pond mold the you made

[track73]

You can also Calculate the volume of the cylinder in CC's one inch down from the deck. Install the piston with rings and put it one inch down from the deck. measure that amount of fluid and subtract from the original amount one inch down.

[Burgess]

I made a fixture to cc the top of a vintage set of Jahn's 455HO pistons. I machined a ring to go around the piston top, also a flat blank to cc the tare volume of the ring. After a slight lathe turning adjustment, I got the tare volume to an nice even 100cc's. Then I cc'ed the piston top just like measuring a head chamber, and subtracted that from the 100.

The dome volume on these things is 18.5 cc's!

[wh33lman]

Some good methods here...thanks.
My winter project is to confirm the exact compression.