I'm about to measure how much my pistons come out of the bore. My question is, do I measure from the piston dome, or base of the piston? I have -3cc pistons and they have a very small dome right under the valve reliefs. I'm assuming I would want to know the highest part of the piston that is out of the hole..? Thanks guys

 

The published numbers for quench are based on the face (flat portion) of the piston not the dome. The dome is taken into account during your measurement of piston to valve clearance, assuming the dome surface is the same surface as the valve relief surface. That does not appear to be the case though based on your picture.

 

I will get a dial indicator on it today and see if the top face is the same as the dome or not.

 

You need to know the deck height of the portion(s) of the piston that are under the quench pad(s) on your heads. This location will not be on the domed portion.

1. Measure deck height in the geometric center of the piston. This will be on the domed portion.
2. Measure the height of the domed portion relative to the rest of the piston top surface.
3. The difference in these 2 measurements will be your piston deck height that you use to calculate quench.

The geometric center needs to be measured first because this will not be affected by piston rock. Another option would be to measure the high and low of the piston edges when rocking the piston by hand, and take the average.