Ok stock specs for my LB9 are this:

Piston Down Bore @ TDC: 0.045"
Deck Volume @ TDC: 8.21cc

I'm going from stock pistons to JE pistons with a -12cc dome. How do I enter that into Desktop Dyno? It wants a new "Piston Down Bore @ TDC" and is asking for a new variable called "Volume Above Piston" to calculate the new "Deck Volume @ TDC".

What do I enter?

 

You use the compression ratio calculator in DD2000. You enter those parameters and head volume.

 

I'm using Dyno2003, here are my screen shots:





The top one is stock, the second is what I need to fill in and I don't know what values to use

 

For the Pistion has dome, dish, or valve relief...

4 - Piston down from TDC is the distance from the deck of the block to the highest part of the piston.

5 - Volume above piston is the volume of water that you can pour into the area above the piston and have it level with the block deck.

So for your car...

Lets say your the distance from the highest part of the piston piston in 0.1 in below the deck height. So, 0.1 goes into the #4.

If you have a burette go fill the area above the piston with water and put that number in #5.

If you don't you can also calculate it.

Lets break the area above the piston up into to volumes the volume that is above the piston if it were flat (volume #1) and the recessed volume of the piston (volume #2).

To calculate volume number one use the following formula where #4 is the distance you entered in DD's #4:

#4*0.785398*(your bore)^2 = volume in in^3

since 1in^3 = 16.387cc we need to multiply the above answer by 16.387.

Take this volume and subtract it from the dome height of your piston.

For your car....

lets sat #4 is .1

.1*0.7853982*(3.766)^2 = 1.11391in^3

Convert this to cc
1.11391*16.387 = 18.254 cc

Next,

18.254 - (-12) = 30.254cc

30.254 goes in #5

So, your car would have a CR of 9.23.


David

 

Thank you very much for taking your time to walk me through that :hail:

Alex