Hi Everyone

I would like to start off by saying this is my 1st post on the forum so please forgive me if I happen to post something where it shouldnt go

I have decided to undertake the daunting task of removing the motor out of my mini to improve its performance. I would appreciate anybodies input

I am not mechanically minded so here goes with what I got

I think I have an 1100s motor, with a mild cam (numbers unknown) oversize pistons (unknown size) was told its cc is about 1310, twin su carbs, oil cooler and remote gearbox
The numbers on the SU carbs are AUD 9203 on both the left and right
Manifold has AEG 347, underneath it 12A661, underneath that the letter P
On the head the numbers I can see are 12G938 on the right and the letter X on the left
I also have a spare bare head with the following numbers
In the middle 12G940 with 315 underneath, on the right 12G1805. It also has other letters and numbers upside down and on angles all over the place.
The block ID reads 12YD Ta H14509.
My question is, Is the bare head a decent or better one than I have on already? What cam, lifters, pistons etc should I use to boost performance. I believe a spring is missing off the carbies cause it idles about 1500 rpm.
I have probably forgotten things to tell you
I do apologise for the lenghty post
Apperciate any help

The Head which is stamped 12G938 is a stock 1100S head and the other, which is 12G1805 is a late Cooper S / Clubman GT. Your block is an 1100S.

Which is the better head to use?

Well, either or both could have been modified at some point. In stock form, both are almost the same, except for valve sizes, valve springs and the Cooper S one will have been drilled for the extra head bolt and stud.

I'd have them examined and crack tested before deciding which one to run with. It is a fairly easy job to have the Cooper S sized valves fitted to the 1100S head.

The pistons will be stamped on the crowns with on over size number (if they are oversized), something like 0.020 (which is 20 thou over).

I'd also suggest either having your cam measured - on every lobe - or have it done for you so you can i) see what the cam specs are and ii) see if the cam is worn beyond service limits.

The high idle speed could be attributed to quite a number of things and / or a combination of these, including but not limited to, cam spec.

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Thank you very much for your advice

Your welcome

Good luck with your project.

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In regard to the twin carbys the AUD9203 number is for just the float bowl lids so more information is needed to identify the source vehicle for this setup. AUD9203 lids were used on single carb Minis, Sprite, Midget, Austin 1800, Marina, etc. It's interesting that both carbys have the same type lid because the Cooper S, for example, has this lid for RH carb and AUD9258 for the LH carb.
Can you post a picture? If not, are the float bowls on opposite sides of the carb bodies? Does each float bowl have a small triangular tag on one of the lid screws? If so the number on it is the carb specification which identifies the vehicle it was designed for.

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ex-NSW Police 1970 MK II Cooper S
VMCI #43

The bowls are on opposite sides of the carbs. I could not find the triangle thingy you were speaking of. I will take a photo on the weekend and attempt to post it here. I will need to get them reco'd if i use them again. I think they are hs4. They have a diamond type fitting bolted to the manifold.
Thank you, I appreciate your advice