How to find your CR?

[Blown Vsix]

I'm having a 4.2 being built for me and I was wondering what #'s I need to get to find my compression ratio. It will be a supercharged motor with new 4.2 crank, forged pistons and rods from SSM.

[Lunchbox]

I would ask the engine builders. They should know, that's what you are
paying them for.

[nikko]

You need volume measurements of the cylinder:

Specifically, CR=Volume of combustion chamber with piston all the way down / volume of combustion chamber with piston all the way up.

All sorts of things can affect this.. like dished pistons, shape and volume of the cylinder head itself, etc...

[Blown Vsix]

Well I went ahead and emailed my engine builder but I dunno if he will be able to give me a final CR yet because the engine hasn't even been cranked yet. I do know the head volume, piston type,etc. as well as some other number, similar to what you get when you do a compression test for a blown HG. I just wasn't sure if I could use that # to get a general idea.
What sounds like a good ratio for a blown 4.3L with all the goodies? I was thinking around 9.1-9.3. but I know there are many factors involved like you said.

[pete]

Being able to crank the engine has nothing to do with compression ratio. Have SSM explain it to you. You deserve it as a paying customer.

[Blown Vsix]

9.3:1 with thick Ford laminated HG's...thanks for the help guys

[Resonator]

http://www.rosspistons.com/CR%20Calculator.htm