what compression would ej20 with over size .05 piston have

Thats impossible to tell, only guess work.. when you Have no idea of dish volume or CC of heads
 
If it was standard pistons swaped out for standard just 0.5 oversize and same headgasket thickness I imagine the same as what you started with
 
Nope as ken said totally impossible..

Wat make pistons, head gasket thickness and wat type heads? Can guess a area but not know exact
 
just roughly talking ...
head cc 48
gasket 7cc
dome volume 18cc on 92mm bore would be 8.3:1

using all the same cc with same dome volume except with 92.5mm bore you would have 8.21:1 ish ..
but when you go oversize you very rarely have the same piston or exactly the same dome volume ..
 
:icon_redface:Learn something new everyday

Is there anyway of calculating it exactly?
 
ali burrows said:
yes ... get the new pistons and give me ur engine and i can calculate the compression for u ...
Click to expand...

Very good, no point taking apart my new engine now though Ali :icon_lol:
 
Although it maybe slight, Heads cc will change everythime they are skimmed, so for talk sake you go and do your rebuild and allow the standard new head cc, your heads may well have been skimmed once or twice before etc etc so you dont know what cc you have untill you skim your heads and get them cc'd. Then you have to take into acount the pistons spec.. Different thickness head gaskets are available to correct and make the comp ratio you want. Also Resurfacing the block will have same effect as skimming head, more you take off the more you will raise the comp ratio.
Most guys can give you a rough idea of what you will end up with from there past experience, but only true accurate way is to measure everything and do the maths
 
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