Mini Cylinder heads - Benefits?

Post by **Shawn** » Sat Nov 26, 2005 1:41 am

G'day All,

I know this has been discussed in past threads, but I just want to confirm in relation to a 948cc engine:

Can a 12G202 (1100 Moke) head be of any benefit?

I believe the inlet valves are bigger - is this the case?
If so, will they clear the bores ok, or does the block need to be pocketed?

I've recently been given three heads all in good condition. (1x 12A145 and 2x 12G202)

By taking rough measurements, the 12G202 appears to have bigger inlet valves than the standard spec Mog (2A629) (at least as far as the BL Minor workshop manual states)

The 202 head also has the port for the temp gauge under the thermostat, so it would suit me to use it.

I've haven't been able to find any detail on line as to the valve sizes on these heads - I've also tried theminiforum.co.uk without luck.

Thanks!
S

Post by **rayofleamington** » Sat Nov 26, 2005 2:14 am

nearly everything you could ever want to know in answer to this question:
http://drcwww.kub.nl/~bogaard/heads.htm

Fromk that link you can probably work out why I've just fitted a 12G940 on one of mine! The big block heads (for the 1275) need to have recessed valves (or machined clearance in the block) when used on the small block (up to 1100). Fortunately this one has recessed valves - unfortunately the 1275 gasket didn't line up correctly with the 948 water jacket so I'm taking a risk using a 948 head gasket (gasket compression seals are therefore a little too close on the head chamber

)
As for whether any particular head will be compatible with a 948 - a small block head 'should' be ok. A big block head will need some work and/or some luck.

Post by **Shawn** » Sat Nov 26, 2005 3:13 am

Thanks heaps - Excellent site - that is exactly what I needed, although it looks like there is no gain to be had (except for the temperature gauge).

Post by **Shawn** » Sat Nov 26, 2005 3:33 am

Ok...thinking further...

If I fit the 202 head, I increase the capacity by 1.6cc per cylinder, but I lower the compression ratio.

What effect will that have on power - or are the numbers too small to matter. (I'm starting with a standard 948, so I haven't got much to give away).

Post by **bigginger** » Sat Nov 26, 2005 1:14 pm

Aha - Hi Shawn, didn't realise it was you on the Oz forum - you got here then!

:D

Post by **bmcecosse** » Sat Nov 26, 2005 6:58 pm

The 202 head is a very worthwhile improvement - it has the bigger inlet valves and the ports are bigger too - square shape. However - the combustion chambers are bigger so the CR will be down. Easy answer - skim the head by 60 thou and you will have nicely higher CR and the benefit of the bigger valves. If you can also find the camshaft (AEA 630) from the 1098 engine that will boost power even further. In fact a 948 engine so equipped can generate the same output as the 1098 engine (48 bhp) but of course at higher revs than the 1098 would be going. It's all to do with air pumping - so a 948 revving at 6000 rpm will pump the same air as a 1098 at 5000 (approx figures used - but you get the idea) - and both will make the same power.

Post by **Shawn** » Sat Nov 26, 2005 8:24 pm

Thanks again guys - I've got access to the cam from one of these too - might be a plan!

Post by **Nigel2** » Sun Nov 27, 2005 10:58 am

Interesting post, I also have a 202 head and AEA 630 camshaft lying in the garage off a scrap 1098 engine. Our 61 Minor still has the 948 engine so like Shaun I will do the mod. If like suggested the 202 head is skimmed by 60 thou will this bring it up to the 1098 8.5:1 compression ratio or higher. The car is used everyday so I still want reliability but a little more 'go' would be a help on some of the hills round here. I did some while ago fit the higher ratio diff from a 1098 in and this has made 60/65 mph a lot less hassle.
Thanks in advance

Post by **Peetee** » Sun Nov 27, 2005 3:59 pm

Just to whet you appetite for inproving the 948, the head to go for is definitely the 12G295. I had one of those and a 1.5 inch SU fitted to a 948. Just those two mods were enough to make it an absoulte hoot to drive. It would easily out-pace, and sounded much sweeter than a 1098, and held 70mph uphill. I'm not one for figures - preferring the way a car feels to 'performance on paper' but just for the record, 0-60 dropped from 30 seconds to 18!

Post by **rayofleamington** » Sun Nov 27, 2005 7:05 pm

Just to whet you appetite for inproving the 948, the head to go for is definitely the 12G295. I had one of those and a 1.5 inch SU fitted to a 948. Just those two mods were enough to make it an absoulte hoot to drive. It would easily out-pace, and sounded much sweeter than a 1098, and held 70mph uphill. I'm not one for figures - preferring the way a car feels to 'performance on paper' but just for the record, 0-60 dropped from 30 seconds to 18!

nice one Peetee - I'm presently fitting all that but with a 12G940 (much bigger valves than the 295). Am looking forward to some umph!
The only hassle so far was the head gasket, but by careful checking the 948 gasket did the job (the 1275 head gasket wouldn't seal the water jacket hole nearest the oil feed).

Post by **Peetee** » Sun Nov 27, 2005 8:38 pm

Good luck with the 12G940 Ray. I tried that with a 1098 and couldn't get it to run right at all. The only solution was to fit a block to match the 940 head - if you catch my drift.

Whoa Joe, Whoa!

Post by **rayofleamington** » Sun Nov 27, 2005 11:47 pm

I tried that with a 1098 and couldn't get it to run right at all.

it's a head I've had for ages - it ran brilliantly on a 1098 with big carb and huge exhaust however the MOT man made me take the exhaust off and fit a sensible one - I'd only had the car 2 weeks

I then ran it for another ~ 40,000 miles with a standard carb and exhaust,. After that I ran a standard head converted to unleaded which I transferred from car to car over the years. This 940 head had been sitting on the shelf for so many years that when i came to use it, I found I'd already nicked almost all the studs for other cars. Ah well - there's another load of time lst

Post by **Shawn** » Mon Nov 28, 2005 6:07 am

Alright - next question - are there identifying marks on the camshaft anywhere? I picked up one in good condition from an old Mini 1100 engine (the same engine as the 202 head came from).

Could not see any marks or numbers at all.

Or, is there a lobe measurement which identifies the cam? This is what I've got. Measurements are approx.

(see how good I am at MS Paint!

)

Post by **bmcecosse** » Mon Nov 28, 2005 8:46 pm

The AEA 630 cam should have 2 rings on the body of the shaft. It should have .250" lift on both inlet and exhaust ( where the older cam had only .235" on the exhaust) - which from your measurements (6.3mm = .252") is about right. This cam was also known as 12G165 in 'pin'drive, and 12G726 in 'spider' drive. May be marked as such. It's by no means an 'exciting' cam - but it is a bit better than the standard 948 cam. If you can get hold of the cam from an MG Metro engine - now that's a whole lot better ! I agree the 12G295 head is better too - but they tend to come expensive these days. The 12G202 (after skimming) will give a useful lift to the performance.