There's something I don't get after measuring a stock B20E head:

Fact: A stock B20 has a bore of 88.91mm. With a stroke of 80.00mm it adds up to a total of 1986cc. The so called big bore B20 should have a bore of 92.10mm to fit the B21 pistons. With a stroke of again 80.00mm this adds up to 2130cc.

Common knowledge: If you would bore a B20 to 92.10mm you should also work on the head so the combustion chambre will match the bigger bore (92.10 in stead of 88.91mm).

Case: I am planning on building such a 'big bore B20'. I have a stock '73 B20E head (deck height 84.9mm) and a '74 8-bolt B20 block.
Now, the thing that strickes me is that the diameter of the (for as far I know) stock B20E head is 92mm.

Questions:
So:
-Does that mean that a stock B20E has a mushroom-shaped combustion cambre?
-Does that mean I shouldn't do anything to the combustion chambre as it is?
Or:
-Would a big bore B20 also prefer a mushroom-shaped combustion chambre?
-Would a larger CC only be for the benefit of unshrouding the valves?*

*the head now has 44mm intakes, 35mm exhaust. I'm keeping stock size intake valves, but larger exhausts.

I think I once measured an B20A-head, and think it had a CC diameter of just 88.91mm (can anyone confirm on that?). So what's the story with these E-heads?

Thanks a lot in advance! Cheers, Ben

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P131, '65, B20B+M47. P131, '69, B20E+AW71L+LSD. (www.tinustechniek.tk)