+20 15cc piston with normal 12g904 head will make CR at 9.88?
Turbo Mini Forums

im worry or its truth? (1293/4+15+21.4)/(21.4+15)=9.88

its so high, i remember stand piston also make CR around 10

You have missed out the gasket volume, ringland volume and deck volume which could make a fair bit of difference.


EDIT - use this, it gives the average values of the missing items
http://www.afracing.co.uk/CR.xls

Edited by Rod S on 17th Sep, 2009.

Schrödinger's cat - so which one am I ???

Well if you put the figures into the spreadsheet including the missing ones you get 8.02:1
If the engine is well built it probably won't have anywhere near 5.25cc deck volume but you really need to measure that one accurately on your own engine.
With a smaller deck volume, the CR will be higher but nowhere near 9.88

Schrödinger's cat - so which one am I ???