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1275 Head On 998 Block Help


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#1 Haz20

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Posted 24 March 2019 - 01:34 PM

I have recently acquired a 1987 Austin mini advantage. I have a 1275 head from a 1998 fuel injected mini. I want to know what needs to be done to fit it to the single carb mini I have now. And if it’s possible.

I have replaced many head gaskets, manifolds and so on so I know how to remove it and replace it aswell as adjusting values. I would just like to know if it would be a simple swap and if the head which was fuel injected will accept the single carb and 998 block without any major modifications.

Thanks, Harry.

#2 Cooperman

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Posted 24 March 2019 - 09:56 PM

It is not just a simple replacement. The edges of the valves in the head from a 1275 overlap the edges of the bores and with certain cams or machined down heads can hit the block deck.
Careful measurements are needed together with volumetric calculations for compression ratio.
It needs to be done properly.


Edited by Cooperman, 25 March 2019 - 06:04 PM.


#3 cal844

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Posted 24 March 2019 - 10:43 PM

The top of the block needs pocketed to allow the valves to open fully.

#4 cal844

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Posted 24 March 2019 - 10:43 PM

The top of the block needs pocketed to allow the valves to open fully.

#5 Cooperman

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Posted 25 March 2019 - 06:05 PM

really not worth doing unles you are building a competition engine for 'up tp 1000 cc class' and need the really big valves of a 1275 head.

With a standard cam and carb on a 998, you will gain nothing with a 1275 head, but will require you to do a lot of engineering calculation and machining.



#6 Retroman

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Posted 26 March 2019 - 01:59 PM

As above

 

After some careful measuring and calculations it can be considered, rarely is it a straight forward head swap.

 

With a standard cam and carb its not really worth doing as you loose out on torque in the lower rev range

 

That said if the block is stripped and the pockets machined to suit a higher lift cam etc then it can be a worthwhile task

 

You will also need a small water pump pulley and use a BK450 1275 head gasket

 

If the engine is in then its easier and cheaper to use a skimmed 12G295 head

 

Or fit 295 size valves and port the head you have






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