8 replies to this topic

[croc7]

I recently bought an 11 stud 12G940 cylinder head, thinking that it might be one originally fitted to the 1275 MKIII Cooper S but after further inspection, the thermostat 'housing' end of the head is not stamped with the number 12G1805 as would be expected on a Cooper S head.  Research on the Somerford Mini site points out that the 11 stud 12G940 head was also used on "high performance derivatives such as the 1300 GT and MG 1300 and the Innocenti Mini Cooper 1300".  So would I be correct to assume, given the information from Somerford, that this head should have the same or similar flow characteristics as an authentic Cooper S head?

[timmy850]

Have you measured the size of the valves? Drilling the additional 2 stud holes is a relatively common modification for higher performance engines

[Turbo Phil]

I personally wouldn’t be to worried whether it’s a factory 11 stud head or not. As mentioned above it’s easy to drill the two extra stud holes.
There’s also nothing special about the “S” castings in terms of flow either.

Phil.

[croc7]

Yes, the valves are 1.4"/1.15".  The exhaust ports look to be normal size and the intake ports still have the provisions for fitting sealing rings so I'm guessing its pretty much unmolested.  The head is in great shape with new valves, guides and freshly re-surfaced.  I would like to know what, if any, upgrade can I expect if I replace the 12G940 that's on the engine now.  Probably none, but will keep on hand as a spare. 

[croc7]

"There’s also nothing special about the “S” castings in terms of flow either."  So with the S, it was all in the camshaft, compression and timing then?  Not arguing, just curious.

[MiniMadRacer]

If I recall correctly only the MK3 Cooper S head had the 1G1805 stamped on the thermostat housing area.

[Turbo Phil]

"There’s also nothing special about the “S” castings in terms of flow either."  So with the S, it was all in the camshaft, compression and timing then?  Not arguing, just curious.

The larger S/MG Metro etc inlet valve (35.6mm) does improve flow over the smaller (33.3mm) valved heads, but what I meant is they’re nothing special as any head can be modified to give the same/better results.
The increase in valve size doesn’t show the gains it could simply because the main restrictions lie in the casting itself.

Phil.

[whistler]

Anyone could have drilled the 2 extra holes in the head. I have a similar head with the extra holes drilled and it's not an S head.

[Spider]

"There’s also nothing special about the “S” castings in terms of flow either."  So with the S, it was all in the camshaft, compression and timing then?  Not arguing, just curious.

 

The Camshafts were slightly different, with the S's that had this head having an additional 10⁰ exhaust duration (seemingly to make up for going to smaller exhaust valves that were in the AEG163 heads), Higher CR (which is where most of their zip came from), better Inlet and exhaust tracts.