Thread: Difference between Spreadbore & Siamese

Originally Posted by Lotz-A-Landies

The head is flat and the inlet valve uses the extension of the bore cavity for the exhaust valve. So while the bores 1-2 & 3-4 have moved apart slightly it has no impact on the position of the valves.

Slug Burner was referring to the inlet valves so as you say the centre of the bores are further apart but the head and inlet valves are in the same place therefore their relationship to the bore centre has changed as I said.