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MG Midget and Sprite Technical - 12g206 and 12g295 differences?
Hi, I have searched the BBS archive and several other sources but I can't find anywhere that lists the differences between the 12g206 cylinder head and the 12g295 cylinder head. I have learnt they both have the same combustion chamber volume and same valve sizes to quote Calver: 12G206 Inlet 1.218"/30.93 Exhaust 1.00"/25.4 28.3cc 12G295 Inlet 1.218"/30.93 Exhaust 1.00"/25.4 28.3cc I just can't seem to find any information on how they vary from each other otherwise. I have a 12g206 on my engine at the moment and am not sure if there is any benefit to changing it for a 12g295. Thanks, Mitch |
M Leask |
From memory, I think they are basically the same thing. I don't think you would notice any benefit. |
Dave O'Neill2 |
The 206 used to crack even more easly than the 295 IIRC If you want an upgrade then I'd suggest a modded 202. As you might have found on CK's website that has the potential to be modded to levels a 295 or 206 can't reach with the bonus of not cracking |
Onno K |
Vizard only notes that the 206 head is "very rare" and I think Onno's comment explains their scarcity !! |
M J Chapman |
Thanks for the answers. It seems their scarcity is the reason not much is written about them. If only it was "very rare" for good reasons :-). I have read a fair bit about the potential of the 202 head and that out of the box the 295 is generally regarded as flowing better. I think if I was to go down the 202 path I would need to plan it much better in regards to compression ratio and engine specs. If there is little to no difference between the 206 and 295 I may as well keep what I've got and try something like a Swiftune SW5 cam as a simpler mod. |
M Leask |
im guessing you got a 1098, if the head Is in good shape, maybe go a 1.5 ratio roller tiped rocker assembly ...that will but some pucker in the spencher...fast simple and not overly expensive prop |
Prop and the Blackhole Midget |
Yep, I have a 1098. I was looking at changing it for a 1275 but the money I would spend on just getting a rebuild-able 1275 would go a long way towards giving the 1098 a bit more go. I have contemplated just throwing some 1.5:1 rockers at it but the cost of a reasonable set is about the same or more than a camshaft kit. The engine will be coming out sometime soon so that I can change the gearbox to something with a synchro on fourth gear. I kind of figure that it is a good opportunity to change the cam to something a bit sportier. I can also source a 12g295 for reasonable price so if it was of any real benefit it was an upgrade as well. |
M Leask |
Go for a good cam (266 or 276) and get a good head. Modded heads are expensive but worth every penny. The asthmatic siamese head is the real bottel neck for any power |
Onno K |
Mitch See pictures and notes on 12G202 head at: http://www.spritespot.com/gallery/sprinzelsebringsprite?page=28 Best wishes Mike |
M Wood |
all I can see is the 12G206 on that page, no 202... |
David Smith |
Thanks for the link Mike, that is the information that I couldn't find. Onno, when you say a good modified head do you mean something like this? http://www.calverst.com/shop1/index.php?main_page=product_info&cPath=2&products_id=88 |
M Leask |
Yep Calver's heads are good ones And he is a guy who can do something special if you discuss your wishes and give him a 12G202 as a base. |
Onno K |
Vizard says the 206 heads are fitted with the same valve sizes as the later 295. I have worked on half a dozen of these heads and still own 2 or 3 castings and I have to say that every single one is fitted with smaller 1098 1.0625" inlet valves not the 1.218" inlet valves most folks state. I am wondering if a mistake has been made in measuring valves at some point or someone once measured a 206 converted to 295 size valve? maybe the ones I have seen are the exception that proves the rule? I am quite happy to see an umodded head with the larger 295 valves as it would spoil my run of seeing 206s with smaller valves. just incase someone is thinking I am confusing the old 1098 heads no I am not they are 202 castings. Having had my moan. The 206 and 295 heads have valve throats too wide giving a 1 mm 45 degree seat and no room for bottom cut. In ye olde days Mini Spares manufactured larger than 1.218" valves to improve the head, sadly these are NLA. A very good mod for all the 206 heads I have seen to date is to fit the 295 inlet valve and get a good valve throat shape with multiple angles. A 295 or 206 head can be fitted with 1275 valves but beware the larger ex valve hits the block unless big cutouts are done on the block. The valves are also 3mm longer or so , this means shimming the rockerposts up... When we mod the 295s we tend to fit inlet seat inserts so we can produce an artificial throat for good flow. I attach a link to my website showing modded heads available 'off-the-shelf'. For the first time ever we have prepared a few A series small bore heads....1000, 202 and 295.. I am not pushing these for sale just linking so folks can see pics of mods. If anyone feels I am trying to use the threads to flog heads I can only apologise but assure folks I am not. We aimed the heads at Mini owners. Since the cars have turned 50, have really got into tuning, restoration and ownershipand we have been busy with heads and dyno tuning. http://www.peterburgessshop.co.uk/CylinderHeads.html Peter |
Peter Burgess Tuning |
Off course Peter has some nice stuff as well ;) Peter I should finaly get pistons now soon and start building my 1293 with the modded 286 you supplied. When I get it running I'll keep you posted. Life does tend to get in the way of car stuff some times.... |
Onno K |
Hi Onno Did you get your pistons from Mini Spares? When I rang them a couple of weeks ago they told me the Megas were back in stock. Peter |
Peter Burgess Tuning |
Nop if they are they won't sell them to me.... There should be a pair of high CR hepolites on their way soon. |
Onno K |
Oh, I only asked about +60 pistons and assumed all the other sizes must be in as well. You wouldnt have thought it would be so difficult getting hold of good quality 1275 pistons would you! Peter |
Peter Burgess Tuning |
<<There should be a pair of high CR hepolites on their way soon. >> Are you building a two-cylinder? |
Dave O'Neill2 |
Peter, Would there be any benefit in fitting a small bore head with 1275 valves compared with dropping on a 1275 head. I fitted a 1275 head to a 1098 years ago for a laugh, it had a 276 cam, and was stunned at the improvement as it really went above about 3.5k rpm when it came on the cam. 40 DHLA carb was on the engine at the time both before and after the change. I pocketed the block to clear the exhaust valves in situ with an improvised guide for a valve seat cutter. The only problem I had was that a coolant passage in the small bore head at the back of the head coincided with the fire ring on the large bore head gasket and caused a small gas leak into the coolant passages due to pitting on the top of the block, later corrected by a small filling of that area with weld and dressing it back flat. |
David Billington |
Sharp Dave ;) David In my mini days me and a friend both had a 998A+ with sw5 the only difference was he used a 1275 head I a modded 12G202. Guess which made more power... I have been told it has to do with unfavorable combustion chamber shape due to the cut outs. |
Onno K |
I suppose it would be easier to get good CR with the 1275 head. We had to use the 295 for a race class so we used the 1275 valves as valve size was free. Peter |
Peter Burgess Tuning |
This thread was discussed between 01/01/2013 and 05/01/2013
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