I guess this quote would aply to me then:

"Because the B18 head and B18 combustion chambers were carefully engineered to match the B18 bore. The shape of combustion chambers is critical in controlling burn characteristics, resisting detonation and pinging while translating the chemical energy in the fuel into kinetic energy in the pistons (we're talking "squish" and "quench" here). What had changed?

A major factor in determining compression ratio is the area of cylinder wall swept by the pistons on each stroke. The swept area rises steeply with an increase in piston diameter -- long story short, the big bore pistons jam an increased volume of gas into the old combustion chambers. The B18 big bore kits therefore come with thick head gaskets (.080" vs. .050") to keep the compression within reasonable limits, effectively increasing the volume of the chambers by making them taller. This results in chambers not only too narrow for the bore, but also too far away from the pistons."

But, yes, I am aware of that. But since the head is an A-head it has low compression. With the petrol here in europe (or LPG which has octane number > 100) High compression would be no prob (better even). I do guess that the burn characteristics and gas flow might be a problem though.

What if I would just cut the edges of the CC on an angle (where they normally match the bore)?? Like so: (blue is B18 bore, green is B20 bore, red bying the new CC shape)



Would that work? (Btw, would that also work for a B20 head on a big bore B20 block?)





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