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looking for a demension that i can measure with a set of calipers, tsp/prc claims to have milled these heads .020" but im measuring 70cc with my econo buret from summit.... never done this before so im not that confident.
With a .020" flat mill, the heads should end up around 66cc's IIRC.
To measure properly, you have to use a flat clear plate sealed to the deck with grease that has a hole in it to get the water in and you fill it until all the air is gone. If you're just putting water in the chamber and eyeballing when it's full the meniscus (dome shape of the water surface) will throw you off.
The chamber should be checked as show in the picture. It's easy to add more liquid than is needed for he chamber due to surface tension of the liquid. Might be worth checking a couple of chambers. Did the paperwork show the shop milled the heads?
Stock LS3 heads are ~68cc +/- 1 cc.
The heads were probably ~ 67-69cc before milling.
This is the ratio of milling I've seen mentioned:
.006 inch milled = 1cc
If the heads are milled .020 we'd expect them to lose about 3.33cc. The new chamber size is would probably be around ~64.67 +/- 1 cc (63.67-65.67cc)
right, i was looking for a dimension i could measure with a dial caliper or micrometer.
i cc'd my heads, using alcohol, and came up with 70cc on 4 different chambers, either im measuring wrong (prolly the case) or PRC did not mill them down .020
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0821 cylinder head dimensions 
