B18A to B18B - how much to skim off head?

[classicswede]

US and UK do not use the same octane rating system so their numbers are lower for the same octane.

[c1800]

Octane methods and differences here:

https://en.m.wikipedia.org/wiki/Octane_rating#/search

[arcturus]

Originally Posted by c1800

Octane methods and differences here:

https://en.m.wikipedia.org/wiki/Octane_rating#/search

Tat's a lot of reading but I get the message

[tdz840]

Whilst I accept the head dimensions in the manual may determine which head you have, there is no guarantee it hasn’t already been skimmed.
At the end of the day the most important factor is the chamber volume:
1. To determine the volume
2. To ensure they are all the same
Next step is to determine the piston height. As mentioned flush (or just protruding) is best for squish. Ideal squish is 0.032’ to 0.035’.
This is why compressed head gasket height is so important.
Once all those factors have been identified you can start to calculate how much material to remove from the face and how much to remove from the chambers.
My car is running 11.7:1 and I have no det. Squish is set at 0.033’ and I use a good quality HG (Elring -eBay #372458960865) that provides the compressed height (0.85). I use Elring as it’s commonly available and cost effective. I would use cosmetic but they are not widely available this side of the pond.
This high a CR required forged pistons, carefully machined bottom end and decked block and a head that I decided was best left to the experts.
Finally if you are chasing numbers you need to ensure the bottom end is strong and tight. No point worn main/conns bearings as this will affect the calculation.
In this case walk back and err on the side of caution- 9.5:1 -10.0:1.
I also use a 123, not because it’s better than OEM/points but because it tends to be more reliable and stable
Russ