Just been comparing combustion sizes on 2 heads
1 head (3 groove collet type) has had the gasket surface machined by about 0.020"
but the depth of the combustion chamber is 0.060" less than a Std 12g940 head
Just wondering how this head will affect comp ratio
I haven't got a pipette to measure the volume
Just wondering how hi comp ratio to go to without causing issues with detonation
Any ideas

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1970 MK2 Cooper S

I am running 11.0:1 with 98 unleaded.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

What head are you running and whats the CC's of the Combustion chamber

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1970 MK2 Cooper S

grab a bit of perspex sheet, stick a 1/4 hole in it, smear some grease around the chamber and use a 25cc or bigger syringe { chemist will look at you funny} pipette bypassed

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120bhp with 450kg just fun waiting to happen

We were prob. drunk when we set it up last and thought this will be a good idea

Casting Numbers, Valve Sizes, CC and Vehicle Fitment

Casting Number Inlet Valve Exhaust Valve Chamber cc Vehicle Fitment

2A628 1.0625/26.99 1.00/25.4 24.5 850, 998 Mini, 948 Sprite
2A629 1.0625/26.99 1.00/25.4 24.5 948, A35, Morris Minor
12A1456 1.0625/26.99 1.00/25.4 24.5 850, 998 Mini, 948 Sprite
12G202 1.156/29.36 1.00/25.4 26.1 997 Cooper, Austin 1100 Square inlet ports

CAM4180 1.0625/26.99 1.00/25.4 25.5 998 Mini A+ (note 3)
12G206 1.218/30.93 1.00/25.4 28.3 Early 998 Cooper, MG1100 Square inlet ports

12G295 1.218/30.93 1.00/25.4 28.3 998 Cooper, MG1100 Square inlet ports
12A185 1.401/35.6 1.22/31.0 21.4 Early Mk1 Cooper S
AEG163 1.401/35.6 1.22/31.0 21.4 Later Mk1 & Mk2 Cooper S

12G940 1.401/35.6 1.15/29.2 21.4 Stamped 12G1805 behind thermostat - MG1300, Austin 1300GT & Mk3 Cooper S
12G940 1.401/35.6 1.15/29.2 21.4 1275GT, Austin 1300, MG Metro, Late 1275 A+ & Turbo (note 2 & 3)
12G940 1.312/33.33 1.15/29.2 21.4 Early 1275 A+ (note 1 & 3)
12G940 1.312/33.33 1.15/29.2 21.4 Single point injection, 12G940B cast at clutch end (note 3 & 4)
12G940 1.312/33.33 1.15/29.2 21.4 Multi point injection, painted black with LDF10… cast at clutch end (note 3 & 5)

NOTES
1) All 12G940 A+ head castings despite all having the 12G940 casting number look considerably different in appearance to the earlier A series ones. Starting with some late mini 1275GT’s in 1979 and in 1980 with the Metro the A+ 12G940 head became sculpted with sunken cast areas / smaller flat areas and lost the main flat area behind the thermostat housing. All A + 1275 engines and cylinder heads have the strong red colour and the smaller engines were all the hideous yellow colour, this applied to both the Metro and Mini ranges, This paint is almost impossible to remove fully even in a hot caustic engine wash tank…

2) The MG Metro Turbo and Mini ERA Turbo both have the same valve sizes as other 12G940 variants but have 8mm stem diameter sodium filled exhaust valves, for improved cooling of the valves. They also have a thinner deck thickness.

3) A+ heads have three collet grooves in the valves and the collets are 14 degree cone taper instead of 10 degree on single groove collets from the A series and the spring retaining caps have a raised ridge around the collet hole. 1

4) SPi Single Point injection heads have no heater tap valve port bored through, no bypass hose and no tapping for water temperature sensor

5) MPi Multi Point injection heads are the same as the SPi but with the flat area for the alternator bracket, with 3 bolt holes below the thermostat housing.

http://www.csgnetwork.com/compcalc.html

Standard head thickness = 2.75 inches

Its an early 12G940, ex racer, chambers have been bathtubbed because it once had flat top pistons and I used it on the road.
Can't recall its chamber volume now without searching, I think about 19.0cc? Has been decked a lot.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.