mk1-forum.net

I'm not one for following trends, and I seem to like to do things a little different.... This could be my failing, but it seems to have got me places so far!

I'm looking out for an 850 engine to go in a mini I recently bought, and the reason I'm after an 850 is to have it tuned, as I've hard they are good fun when they are!

Idea so far:

12G202 head, twin Amal carbs, and I have a 1275 box...

Questions are:

Will the 202 be a good head to go for? (I have one spare and I don't have a 295...)
There seems to be a billon types of amals out there... Im looking for the ones from the 850 commando... Am I on the right lines??
Do you think a cam upgrade would suit? If so, which one??
Am I mad?

Help muchly appreciated!

Ed!

On a small motor wild cams have a larger effect than on a larger engine, but a torque cam doesn't give much 'cus there isn't much to give. I would think a MD286 maybe would barely be streetable. Definitely go for as much compression you can get, big valves and high revs. Maybe a 12G940 head I don't think you can skim a 295 head enough for this application and you absolutely have to have flattops. Really high revs are the only thing this engine has going for it. The big valves of the 940 would help with this.

Hmm... would I have to pocket the block for the 940 though??

What sort of compression should I be aiming for??

I don't want it too rough, perhaps i shouldn't cam it??

I have some 1.5 rockers.... would these be any good??

Sorry for all the questions!!

Ed

I'm sure there are others on this forum who have actually done a performance 850. Of course the Vizard book has good pointers, but from what I've heard, with standard pistons, not over 9.5:1. With the small displacement a small combustion chamber is necessary for high compression and high compression is necessary for higher performance. None of the small bore heads are good for high compression except the original 12A1456, and that's severely shrouded around the valves, leading to terrible flow at high speeds (the one redeeming part of an 850). The 202 needs 60 to 80 thou removed for this kind of compression. The 940 has big valves and good flow. Pocketing may not be necessary if you use a mild lift cam and original rockers. It needs standard to 10 thou for this compression.

I drove my Frogeye for years with the 950 and Cooper S head...

It was still slow compared to the 1100 which is slow compared to a 1275.
But for fun it could be a cool project

I'm planning something similar myself. Most likely a 202 head, pair of H1 carbs on an Alexander manifold and a Cooper 997 cam. I'm after a period engine with a couple of performance improvements, I'm not expecting to win any land-speed records.

Tim

I found this on a google search

"From experience, the 12G202 forms a very good basis for 998cc tuning. However, it needs to be skimmed dramatically - >0.060" in order to get the compression ration up to a suitable figure in the smaller displacement engine. There is a danger of cutting into the rocker oil feed gallery above this figure, although I have frequently removed near 0.090" from there heads. They can also be modified and fitted with the larger inlet valve to produce a "poor" man's 12G295. "

But they are still a closed chamber head and would need some "opening" to be usable... which would again require even more skimming. If I didn't have three 12G295 heads laying around, I might even try this.

Well I have a 202 lying about, my 295 went with my 1100 engine when I sold my minus... I'll get it skimmed then! Although I do have my austin 1300 engine, so perhaps the head off that?? Although I'd be so scared of the valves hitting the pistons!!

I was aiming to just do this as some fun, and use what I had, rather than spend loads of money! I have the Vizard book, So I'll have a read....

Thanks for the info!!

Any more you can shed light on? would the 940 just need the standard cam and rockers? or can you put an interesting cam in?

Ed

Was not Clive Trickey the guru of 850 tuning????

Cheers, Ian

Forget the 940 head on an 850 unless you're racing it. It will wipe out the mid range. Get a properly modified 202 or 295.

Right....

Well I have a 202, and a 940, Im not after spending much, which isnt what im guessing i should be saying to you all!!

picking up my engine tomorrow, Picked up my amal carbs today...

The most powerful high revving 850cc A-Series Mini engines were those built with special Longman short stroke steel cranks for Special Saloon Racing Mini's in the 850 'Free-Formula' class back in the 1970's. The 850cc class was full of destroked/overbored 970 Cooper S engines usually running exotic 8-port heads and the like.
Quote- "the stroke's so short the pistons only quiver in the block!!"

Then along came Gordon Allen's ultimate 850cc Mini.........
viewtopic.php?f=4&t=2675

Sounds like an interesting project.

However, regarding the Amals. These ARE NOT easy to tune correctly & if you don't have an Amal specialist with a rolling road built for a car & a massive selection of spares, jets, slides etc. The chances of getting them running spot on are very slim indeed. Also with Amals being a fixed slide your fuel economy will be absolutely appalling.

I have run an 850 on Amals and although the performance was OK & the noise was ABSOLUTELY FANTASTIC! They only stayed on for a matter of weeks before I went back to SU's.

If I was you I'd go for twin H1's or H / HS2's a 202 head & high lift rockers, a good exhaust & manifold.

In my experience much more tuning on an 850 leaves you with a car that is pretty unpleasant to drive.

M

Thanks for the input!

Im not looking for a 10K revving race machine... just something a little different!

I've picked up some Amals for dirt cheap, that came off a running Norton commando, I'd like to give them a go, I have some twin HS2's spare, so If I get really fed up, Ill slap them on!!

I think I'll go with the 202 I have, get it skimmed, I have some 1.5 Rockers, would these be a bit overkill?

Picked up a complete 850 engine off eBay for £50, so Its all go!

Ed

I wish you luck with the AMALs, I have them on my British bikes, and they are great carbys - but they are set as the factory intended them. Altering their tuning has become a dark art these days. As Mark points out, the problem with them is the number of variables that you need to get right for them to be correctly tuned.

With an SU you need to select the correct needle (not always easy in itself) and set its position. With an AMAL you have an idle circuit, a slide cutaway, a needle position, and a jet that all have to correctly selected and/or adjusted. They are also much less tolerant of wear than an SU.



The other inconvenience with them is that they need to be 'tickled' when starting from cold, which is easy on a bike but more of a hassle when you have to open the bonnet to get to them. There may be a late version that just has a choke and doesn't need to be tickled, but I'm not sure. It would be possible to rig up some kind of remote tickler though, if it was a real problem.

Personally I love the idea of them as part of a period tuning set-up on an 850, but as far as I'm concerned they are just too hard. Once you get yours worked out though, I'd be happy to copy what you've done

I like the sound of what you've got planned, keep us posted with the progress.

Tim

Tuned 850? Supercharge it!

John

Thanks for that Tim!

I have bought some Amals off a Norton commando... A chap at work has one, so im sure between the two of us we'll get it sorted!! I was aware of having to tickle them, and I was thinking of a choke cable which pulled a lever onto them, mounted on the manifold (which I will be making anyway)



A supercharger eh? Wish I had a Shorrock.... *goes to look on eBay*

Ed

ted

as you work with vintage cars, surely you will know that you can to utalise a smaller 'choke' carb, which will remove the need to mod the amals.

you will then, of course, be able to boast that you mini has tripple carbs!

my dads speed 25 alvis has one of these little choke carbs, it does the business to get it going

Yes I'll have to route around and see if I can find a Rolls starter carb spare!

chap at work, who is into his bikes, said that the ticklers were to over fuel the bikes so they were easy to start... as the old Nortons were twin cylinder, and weren't 180 degrees out, so took some starting... he said that with them on a 4cyl then just the choke may be sufficient... We shall see!

I wouldn't have thought that those Amals from the Norton would work. They are from a twin cylinder 850, not an in-line 4. Surely the air velocity per intake stroke would not be high enough for them to work. The air volume per intake in the Mini 848 would be half that of the Norton due to having twice as many cylinders.

Ted.

My chum had an old mate Bill G who worked at Abingdon back in the 60's (engineer+special tuning). They had several mad lash ups. One of the blokes had a 1275s and another had an 850 mini with an aeroplane cabin blower (roots supercharger) in the PASSENGER FOOTWELL. From what I remember, it was considerably faster than matey's cooper s, as well as some Triumph with a V8 engine which was a lash up. I remember a comment about something transmission lasting about 2 weeks and there being loads of fuel in the oil and them having to keep changing the oil. However, it was the fastest mini at abingdon for a time. I think it got sold to someone who crashed it.

So, 202 head, or a 1098 head and a floor mounted blower.