Offset boring for head conversion.
Turbo Mini Forums

Wonder if any of you knowledgable folk could help. I'm currently building an 999 8 port but as a side project am also wanting to undertake a cylinder head conversion. The cylinder head I have has come from an engine that had a bore spacing of 79mm (centre to centre). Is it possible to offset bore either a small bore or a large bore block to this sort measurement?? Ideally I'd like to do it on a large bore block as I intend to use a spare 970s crank I have alongside the twin cam head.

Any help would be fantastic. Thanks

No chance. The outer cylinders would need to be moved outwards about 4mm, stretching the overall centers by 8mm or so. You would certainly machine into the oil galleries on cylinder 4. Just search on here for sectioned block to see what im talking about.

Any engine with cylinder spacing arround 76mm should be do able

Excellent, thanks for that. I'll take a look at the cut out block. I know I can get away with 2 small pockets being machine in the deck but I'd like to avoid that? What's the stock spacing out of curiosity?? Both by freshly bored blocks here are offset bored so can't measure for sure. Thanks

The A series block is a bit funky as there is no uniformity in cylinder spacing. What i mean is, the spacing between 1 and 2 is different to 2 and 3. From memory average spacing is about 75mm give or take 0.5mm

This is picture of interest. The oil gallery from the oil pump to the oil pressure regulator, and the oil gallery up to the external feed pipe.

1275 Bore spacing is 3" between 2-3 and 3.030 for 3-4 and 1-2
76mm = 2.992 77mm = 3.031 after that it would be hard to get more bore spacing than that. But more could be possible with wet liners.

Racecar spelled backwards is Racecar

Thats brilliant, thanks fellas. I have been considering liners but am unsure as to how doable it will be and if there will be enough support around them? Cant say ive ever put sleeves in an A series.