Calculating compression with new pistons.

[Bludger]

say a dc2 vtir b18c2 has a stock compression of 10:1

and the new piston specs are as follows.






new compression is 11.855:1

is this right?
am I doing it wrong?

if so, what is the correct method to calculate compression?

[Bludger]

not taking into consideration head and block modifications of course.

[trism]

Well, does the +5 mean +5 over stock, or +5 as an overall measurement?


edit: because IIRC, stock piston dome is about 2.52cc

so its either 5cc

or 7.52cc

if its 5cc, CR will be 11.1

if its 7.52 itll be 11.7

[TODA AU]

am I doing it wrong?

You're doing it wrong.
+5 is the piston dome capacity
Size is 81.00 (Std bore)
With given comp height on an unmachined B18C2, the compression would be 11.2:1
- Using OEM head gasket.
Take 0.005" off the head & 0.005" of the deck of the block & the comp would be 11.5:1

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