Roger that. Each insert is similar to shaving a the head without doing any other work. Volume of the chambers remain the same.
So if you can get the black insert with a squish around that 1-1.3mm range, you'd better have some really good fuels available. Not to mention the effect all that comp has on top end/over rev.
On the 300 I found the black insert had an acceptable UCCR, but had to use 1.3mm to time the ports for top, which gave 1.9mm squish clearance.
You should see if the factory can do up various chamber volumes!
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