how to calculate new CR?

[cuore_sportivo_155]

Does anyone here remember how to calculate your new CR if you know the old one and the cilinder CC? I used to know, but forgot now...

Someone wants to fit 1mm shorter conrods to achieve a lower CR in his engine for a turbo conversion, btw...

[AlfaJack]

Bit late but I found this:
http://www.muller.net/sonny/crx/compression/

Hope it is of some use :)

[Juan AR155Q4]

CR = (Comb chamb Vol + Cyl Vol) / Comb Chamb Vol
-> Comb Chamb Vol = Cyl Vol / (CR-1)
You have to calculate the original Combustion chamber volume, then add to this the volume generated from shorter con rods.
With this result you recalculate the CR using the first formula.
Remember that the Cyl Vol is equal in both.

Ps: I used to have a calculate sheet, but can't find it right now.

[cuore_sportivo_155]

cheers juan, that's the one i used before...