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12G1316 V 12G940
https://www.ausmini.com/forums/viewtopic.php?f=2&t=88421		 Page 1 of 1
Author:  Phil 850 [ Sat Jan 24, 2015 5:22 pm ]
Post subject:  12G1316 V 12G940
I have a 12G1316 head on my 1100S (1275) and I have also a 12G940 in good original condition.
Without removing my 12G1316 can someone tell me the differences and should I fit the 12G940 and what improvements would there be ?

Thanks in advance
Phil
Author:  drmini in aust [ Sat Jan 24, 2015 5:28 pm ]
Post subject:  Re: 12G1316 V 12G940
They have the same valves (except Cooper S 940 head has bigger inlets), combustion chambers, and ports. Some 940 heads are less restricted in the exhaust ports at the valve guides, but most are much the same as the 1316.
If porting a 1275 head, there is really no difference between the two. Vizard says the port walls on the 1316 are thicker in places. He may be right, I'll defer to GR's experience on that one.
I have done big porting jobs on both, years ago.
Author:  Phil 850 [ Sat Jan 24, 2015 5:37 pm ]
Post subject:  Re: 12G1316 V 12G940
Damn, $250 I didn't need to spend.
Guess I should have asked on here first.
Thanks Doc
Author:  drmini in aust [ Sat Jan 24, 2015 6:03 pm ]
Post subject:  Re: 12G1316 V 12G940
Phil 850 wrote:
Damn, $250 I didn't need to spend.
Guess I should have asked on here first.
Thanks Doc


Both 940 and 1316 heads are getting harder to find in good condition.
I'm sure someone will grab it quick if you put it in the for sale forum.
Author:  Phil 850 [ Sat Jan 24, 2015 6:55 pm ]
Post subject:  Re: 12G1316 V 12G940
My engine has "a bit of a cam" according to the person that gave it a tune.
Should I have my spare head ported and larger valves and 1.5 rockers fitted for more vroom.
What increase could I expect assuming everything else is set up properly.
I also have 1-3/4" SU to install.
Author:  drmini in aust [ Sat Jan 24, 2015 8:48 pm ]
Post subject:  Re: 12G1316 V 12G940
The secret to getting power from an A series is the camshaft.
I have seen 103-107.5HP on GR's engine dyno from 1330-1360 motors with a stock head (S inlets), Minispares 1-3/4 intake and a single HS6. Cams were RE83 with 1.3 rockers, and RE13 with 1.5 rockers.
Graham has designed better cams since then.

Head work properly done helps HP, but it takes time. Time = $$$$.
Author:  VulcanBB18 [ Sat Jan 24, 2015 8:52 pm ]
Post subject:  Re: 12G1316 V 12G940
drmini in aust wrote:
They have the same valves (except Cooper S 940 head has bigger inlets), combustion chambers, and ports. Some 940 heads are less restricted in the exhaust ports at the valve guides, but most are much the same as the 1316.
..snip.


Just to illustrate Doc's point here -

Restricted type 940/1316 exhaust port :

Image

Open type 940/1315 exhaust port :

Image

The open type above is a 1316 I have, I also have a 940 from a 1100S with the same ports, look like the head to choose to me :)

cheers,

Jacob
Author:  drmini in aust [ Sat Jan 24, 2015 8:55 pm ]
Post subject:  Re: 12G1316 V 12G940
That restriction is easy to fix with a die grinder.
Just press the guides up a bit with a stepped punch, grind the bosses with a carbide burr, press guides back down. Easy....
Author:  VulcanBB18 [ Sat Jan 24, 2015 8:57 pm ]
Post subject:  Re: 12G1316 V 12G940
drmini in aust wrote:
That restriction is easy to fix with a die grinder.
Just press the guides up a bit with a stepped punch, grind the bosses with a carbide burr, press guides back down. Easy....


For sure, but if folks are looking at two parts to "bolt on", well might as well go for the open one if you can. Not everyone is endowed with your metal grinding skills Kev :mrgreen:

cheers,

Jacob
Author:  Phil 850 [ Mon Jan 26, 2015 1:22 pm ]
Post subject:  Re: 12G1316 V 12G940
I took some photos (not as well as Jacobs though).
I think my 940 has "open" exhaust port.
Image
Looking in the exhaust manifold port
Image
The current valves
Image
Author:  GR [ Mon Jan 26, 2015 2:44 pm ]
Post subject:  Re: 12G1316 V 12G940
Hi phill 850
Don't be worried about the boss in the exhaust port a std one of those heads (12g1316) will flow 92 cfm @.300" lift and 98 cfm @ .400" lift and that is corrected figures at 25ins on the end exhaust port, which is enough to make a lot of HP.
BMC right through the ages on all there motors be it A/B/C series there exhaust flow on nearly all there heads will out flow the inlets and the did this to achieve good fuel economy, a good example of this is with the MGB they flow a massive amount of air in come parison to the inlet, with the small bores they all run a 1" ins exhaust valve which will out flow the inlets, wait till part 3 of the 68mm project comes out you will see the flow on the exhaust port you will find very interesting.
Graham Russell
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