1.2 bottom ends

[burgo]

would a 12st bottom end work in place of a 12nz one?

[Adam]

No

They have different bores.

[burgo]

what as in different size??

[Adam]

Yesah the bore size is different.
SPI(NZ) block is smaller.

So it will have a big effect on compression if you bolt a carb head to a spi block.

[burgo]

other way round actually, was gonna bolt spi head to carb block. i take it it is a no no tho

[Adam]

Spi head has a smaller chamber, so it would push compression higher than std carb head.
How much higher im not sure.

You could measure the cr...

[burgo]

do you know the bore of the two bottom ends?

[burgo]

i have two :P

[Stuart]

haynes

[Riggy]

12st = 77.8 mm

12nz = 72.0 mm

from haynes :thumb:

[burgo]

****e, big difference. oh well at least i know it wont work

[mowgli]

the 12st is 77.8 bore 61 stroke 9.2:1 cr
the 12nz is 72 bore 73.4 stroke 9.1:1 cr

using st pistons with a nz crank would make a theoretical 1395cc engine.
I will check piston height & little end compatability.
********
Just checked, it won't work. the conrods are different