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Engine Compression Ratio & Head I.d.

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Model casting Inlet diameter Exhaust diameter Compression standard Bhp standard
1300 America, 1275 Spridget,mini 1275 GT and standard Metro 1 5/16"
33,33mm
1 5/32"
29,53mm
8.8:1 (GT) 56 (GT)
'S' units, MG metro, 1300 GT,'90's Cooper and Sprite Tbi 1.4" (TBASE page 161 (2nd edition))
35.56 mm
1 5/32"
29,53mm
19-2-2002- from the yahoo.list: "Dear all
FB has probably seen this already,but it appears the Maestro/Montego 1275 models used the MG Metro big valve 12G940 cylinder head and cam to produce 69bhp.
According to Haynes they started off with 1.312" inlets and 1.156" exhaust valves.But from engine No.12H999104761 and 804102434 they had 1.4" inlets.Which is worth about 5bhp.Get down that scrapyard!
IAN Nicholls"
MG Metro Turbo 1 5/16"
33,33mm
1 5/32"
29,53mm sodium cooled
9.4:1 94
1.3i minis with cats 1991 on 9.4:1
1991on injection minis 10:1 54
63 for Cooper
1990-92 non injection coopers 10:1
1000s with cats 1989 on 9.6:1
1000s 83-89 10.6:1
CooperS mkIII 9.75:1
Different heads to the A-series engine
compiled by Jerker Johansson,Sweden 1987
From the book: The Sporting Minis by: John Brigden ISBN: 0-947981-40-3
Number of Casting Inlet Exhaust Volume Normally fitted to Fits also

2A629
2A628
12A1456
1 1/16"
26.98mm
1"
25.4mm
24,6cc 850 Mini, A35,A40,Minor, SpriteMkI 998,1100 and Cooper
12A1458 1 1/16"
26.98mm
1"
25.4mm
24,6cc late 850 &998 as above but a hole in the front for temp gauge
12G185 (and/or marked as 12A185 * ) 1 1/16"
26.98mm
1"
25.4mm
24,6cc 997 Cooper fits as bigvalvehead for 850 & 998
12G202 1 5/32"
29,53mm
1"
25.4mm
26,1cc Austin/Morris 1100
and/or 997 Cooper *
As above but square formed inlets
12G206 1 7/32"
30.95mm
1"
25.4mm
28,3cc Early MG 1100 upgraded 12G202
12G295 1 7/32"
30.95mm
1"
25.4mm
28,3cc 998 Cooper
MG 1100
Sprite MKIII
Fits on 998 when bigger valves are needed
12G940
9 Bolts
1 5/16"
33,33mm
1 5/32"
29,53mm
21,4cc 1275GT,A/M1300
Sprite MK IV
Marina 1,3
Can be modified to the specifications below
12G940
11 Bolts
1 13/32"
35,6mm
1 5/32"
29,53mm
21,4cc Austin 1300 GT
MG 1300 MK II
late Cooper S
Fits on 1275 Gt when bigger valves are needed
12A185
AEG165
AEG163
1 13/32"
35,6mm
1 7/32"
30.95mm
21,4cc Cooper S Can be used instead of the 11 bolted 12G940
12G940 1 5/16"
33,33mm
1 5/32"
29,53mm
21,4cc Turbo MG
12G1316 1 5/16"
33,33mm
1 5/32"
29,53mm
21,4cc ?? 1275 Austin America The 12G1316 is the Austin America smog head. It's a really beefy head and Vizard liked it because it had plenty of room for modification. There isn't a lot of information on modding these heads, I suspect, because they were not generally available in the UK. It's quite probable that Vizard knew of them through APT.

They are a good solid head, same valve size as the standard (non-MG) 12G940. I think they are a good choice.

Cheers,

Kelley
CAM4180 1.0625" 1"
25.4mm
25.5cc 998 Mini A+ and lead free Last modified: 22 September 1996, with facts from Frans Marx

  

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