True 3.0 compression ratio (its low)

I measured 3 different styles of 3.0 pistons.

1997 3.0 (supposed 9.3:1)
1994 3.0 (supposed 8.9:1)
198x 3.0 (supposed to be 8.85, its a full skirt piston with thicker old fashion 1.5, 1.5, 4mm ring pack)

Every single pistons measured 12.5cc dish, even though they are completely different castings.

I have measured a stock head in 2006 and I believe it was 47cc. Heads I ported for myself back then were around 51+cc (BIG...) Ed Kelly measured and found 46-47cc for all chambers, and I am assuming the motor he measured was around a 1990 model.

Measuring OEM used headgasket, this leaves 3.0L SOHC 12 valve compression ratio

8.19:1 for 46cc head
8.3:1 for 47cc head.

Super low! Its too bad the top ring land and intake valve relief are so close together or we would be able to make a lot more stock piston power safely.

If you look at JE brand shelf pistons sold for vR4, which has a 43cc chamber (much smaller),
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Part # Bore Oversize Stroke (mm) Rod (mm) C/D (mm) Head CC's C/R With .040 (squish) Dome CC's

321330 91.1 STD 76 141 31.5 43 8.0:1 -15.5
321333 91.1 STD 76 141 31.5 43 9.0:1 -6.5
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Shows how deep our 12.5cc dish is for a much larger combustion chamber!!!!!

That is very interesting. Thanks for posting those numbers! I always suspected that the combustion chamber volume was actually the same on all of the motors. I've owned all three "different" generations of 3.0l and they all look the same as far as the combustion chambers and piston dish. I measured from the wrist pins to the crowns and that's the same too. IIRC The top ring on the 87' full skirt piston is slightly lower making the distance from the ringland to the valve relief larger but I still broke 2 of those with the blower. Good find!