Trying to figure out different compresion ratios, Only part I don't get is for instance, in dyno 2003, piston down from tdc? and volume above piston?

these are the pistons i have

Keith Black Hypereutectic Pistons: UEM-KB122020-8 - summitracing.com

anyone help me out? what do I fill in for those two categories?

 

I just woke up so bear with me here......

See the spec called "compression distance"? That's the key. It's the measurement from the flat top part of the piston (not the dome or dish- the flat part) to the center of the wrist pin.

Take 1/2 of your stroke length, or 3.75 / 2 = 1.875
Now add in the rod length, or 6" in this case as that's what the pistons are designed for. 1.875 + 6 = 7.875
Last, add in the "compression distance" of the piston, 1.130 in this case. 7.875 + 1.130 = 9.005" total compression height.

Subtract that from your block's deck height, which is 9.025" for an unmilled stock small block. 9.025 - 9.005 = .020"

That's how far the piston will be "in the hole", theoretically, at TDC.

 

It should calculate the volume for you, once you give it that measurement. Or else you can do the math...
I'd measure this, since you now have the motor apart. Rotate to TDC and use a straight edge and feeler gauges.

 

I know my block has been zero-decked if that helps at all.

 

Zero decked to those particular pistons? Or to your previous (different) pistons?

You'll notice I used the word THEORETICALLY in my explanation. That's not by accident. As with anything involving specs in a high performance engine they must be checked against actual real-world measurement to make sure theory and reality are in agreement.

This is 2 days in a row that I've replied to this tread immediately after waking up.

 

You rule Damon, It was zero decked for these pistons.