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1275 head on an 1100 advise please
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Author:  mini ute [ Sun Sep 14, 2014 1:36 pm ]
Post subject:  1275 head on an 1100 advise please
I am going to put a 1275 head 12G940 on my 1100 motor and would appreciate any advice. My reason is that although it has been bored out 60 thou, lightened fly wheel with twin 1 1/4,s an extractors when the mini spots a hill it runs out of grunt. Is there any problems with this conversion that l need to know about ??
Author:  Mick [ Sun Sep 14, 2014 1:52 pm ]
Post subject:  Re: 1275 head on an 1100 advise please
There is the old valve clash with the top of the block problem. The widest point on the valves are wider than the bore of the 1100 block, requiring a very low valve lift, or the top of the block machined to accept the 1275 valves pushing down from the top. Thats the worst of the problems, but quite involved as you need to tear down the engine to machine the block.
Author:  Scoop [ Sun Sep 14, 2014 2:40 pm ]
Post subject:  Re: 1275 head on an 1100 advise please
You might be better off doing a bit of head work to the current head and get a better cam to give you a bit more torque. Just my thoughts tho. From my understanding the 12g940 would only be an upgrade at high rpm.
Author:  drmini in aust [ Sun Sep 14, 2014 7:06 pm ]
Post subject:  Re: 1275 head on an 1100 advise please
Scoop wrote:
You might be better off doing a bit of head work to the current head and get a better cam to give you a bit more torque. Just my thoughts tho. From my understanding the 12g940 would only be an upgrade at high rpm.


People say this, however a stock 940 head flows as well or better than a 295 one does.
To get equal flow from a 998 head or a 1098 (12G202) one, you would need to spend up on porting and bigger valves.

I put an 1100S one (mildly ported) onto a 1098 bored to 1220cc back in 1968, and it flew. Motor then had a 544 cam and twin HS4s. It was doing mid 16s 1/4 mile times at Castlereagh drag strip on 145-10 Olympic GT radials..
[edit] Yes it was a road car.

Don't try this method at home:- I notched the block (in the car!) by using a die grinder with a 50mm stone, and a vegemite glass jar's steel lid sitting on the piston to set the depth. I used an 850 head gasket to trace the shape and I cut the notches .090" deep.

[I was a poor apprentice back then, these days I would put the block on the mill and notch it properly]. :mrgreen:

[edit] typo
Author:  mini ute [ Mon Sep 15, 2014 5:55 pm ]
Post subject:  Re: 1275 head on an 1100 advise please
Ok thanks for the imput guys might run with just doing up the original head
Author:  TK [ Tue Sep 16, 2014 5:05 pm ]
Post subject:  Re: 1275 head on an 1100 advise please
if you have a stock cam in the 1100, the block and 1275 head haven't been skimmed well you shouldn't have a problem.
Author:  willy [ Wed Sep 17, 2014 1:48 pm ]
Post subject:  Re: 1275 head on an 1100 advise please
Don't do this!
Image
Author:  drmini in aust [ Wed Sep 17, 2014 4:52 pm ]
Post subject:  Re: 1275 head on an 1100 advise please
willy wrote:
Don't do this!
Image


WHAT THE.... :shock: :? :roll:

No way you need to go that far out. I shaped it to an 850 gasket, then used a 1275 one for the head. It was a copper one, back then they were the best. :lol:
Author:  ykg2s4 [ Thu Sep 18, 2014 6:42 pm ]
Post subject:  Re: 1275 head on an 1100 advise please
Hi,
Does any one have a picture of what the notching should look like?
Author:  69k1100 [ Sun Sep 21, 2014 10:24 pm ]
Post subject:  Re: 1275 head on an 1100 advise please
Image
Author:  ykg2s4 [ Thu Sep 25, 2014 7:54 am ]
Post subject:  Re: 1275 head on an 1100 advise please
thanks for that.
Author:  boomini [ Wed Oct 01, 2014 11:50 pm ]
Post subject:  Re: 1275 head on an 1100 advise please
Excuse me for being a dumb f#@* but whats with using a 850 head gasket to mark out where too notch?


Rodney
Author:  drmini in aust [ Thu Oct 02, 2014 1:03 pm ]
Post subject:  Re: 1275 head on an 1100 advise please
boomini wrote:
Excuse me for being a dumb f#@* but whats with using a 850 head gasket to mark out where too notch?


Rodney


The 850 gasket available back in the 60s was `slightly' smaller across the chamber than a 998/1098 one. But perhaps now they are NLA so just use a 998 one- but when grinding or milling, stay a bit away from the gasket sealing area or you will blow gaskets.
Author:  Keith C [ Sun Nov 16, 2014 8:33 am ]
Post subject:  Re: 1275 head on an 1100 advise please
Fitting the 1275 head without the need to pocket the block is entirely feasible. You need to get your hands on Mini Expert Issue One where I covered this application in great detail. You can download it from www.zinio.com - I hope! If not, keep your eyes peeled on my website as I will be up-grading the site to get all this info from there soon - www.calverst.com
Author:  Irish Yobbo [ Mon Nov 17, 2014 12:55 pm ]
Post subject:  Re: 1275 head on an 1100 advise please
drmini in aust wrote:
Scoop wrote:
You might be better off doing a bit of head work to the current head and get a better cam to give you a bit more torque. Just my thoughts tho. From my understanding the 12g940 would only be an upgrade at high rpm.


People say this, however a stock 940 head flows as well or better than a 295 one does.
To get equal flow from a 998 head or a 1098 (12G202) one, you would need to spend up on porting and bigger valves.

[edit] typo


I've been looking into doing something similar with a small bore engine, but it seems that everybody has a different opinion on the heads. Graham Russell's project small bore site is a good read, and he reckons that the 295 head is better than the 940 for small bore engines.

What difference would one expect from using a 940 vs a 295? I would have expected the 295 to have better low down torque and the 940 to have better top end power?
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