Cooper S 1275 - when did it go 1293 cc?

I've just finished researching the 1964 BSCC (BTCC) for my site. This was the year that the 1275 Mini Cooper S was first raced. In early programmes, some entries were 1293 cc, but later in the season every entrant seemed to stick to 1275 cc.
I'm sure I read somewhere that Broadspeed actually was the first one to be able to increase the bore to get 1293 cc, but I can't remember where I read that.
Does anybody know here if in 1964 1293 cc engines were used at all?
It's a tiny detail of motorsport history of course (just 18 cc...) but I'd like to get my data right.

The 1275 Cooper s was on standard bores: boring to plus 60 thou gave a swept volume of 1293.

Homologation allowed re-boring to within standard factory recommended limits.

Since the then saloon class limit was 1300 c.c and as every little helped, most competitive race and rally cars were 1293.

All of our 1275 s cars were run at 1293 c.c.

I know the cars could be re-bored, but my question is was that been done from the start in 1964 or was it later?

Race programmes are not in fact always a very accurate reference source!

The actual official size of the Cooper s in this official configuration was 1,275 c.c.

However, most race and rally engine builders over-bored to +20 thou as a matter of course. (n.b. Correction to earlier post, 1293 c.c. is +20 thou, not 60 as I stated earlier: it's been a few years!).

I can try and find out for you as my best friend (and oldest one too, as we have been chums since we were at school in the early 50s!) is one of the leading figures in the official heritage Mini Cooper Register.

As to when, exactly, that the first tuner discovered the slightly extra bore size would have probably been the first day +20 pistons became available!

It is worth remembering that the Cooper s engine was based on the works XSP dry sump. 1,000 c.c. Formula 3 engine, which used forged steel crank and rods, duplex timing chain and the extra stud in the head, which was a special casting to accomodate the larger inlet valves.

From memory, forged pistons were an homologated option for the s, in all three sizes.

In all probability, privateers would have had to wait until Hepolite (e.g.) came up with suitably strengthened +20 thou pistons to allow the extra swept volume; whereas Abingdon would have used them on competition cars from day one.

the capacity hike is the same principal as Fords engines, the twink was 1558 but most where overbored 20 thou to 1598cc . . .squeeze every little drop under the 1600cc class limit

Plus 20 = 1293
Plus 40 = 1312
Plus 60 = 1330

From what I've read, and generally speaking, 1310 (1312cc) was a much more popular capacity (other than works cars).....in the period :)

Excepting, of course it would have then been outside the class limits (1,300 cc.) for both saloons and rally cars.

Many people tried some amazingly silly things!

Like taking standard mini blocks to 1,700 c.c..

I saw some interesting blocks which would have probably been classed as air-cooled! Some strange shaped con-rods and some amazingly Daliesque pistons...............

The core problems with the whole A series was the three main bearings; the siamesed centre inlet ports and the fairly poor block castings and thin walls.

That's why Ford became supreme. Plus the basic over-square nature of the 105E onwards range, of course.

And later on the cross flow heads.

And later on the cross flow heads.

better gas flow maybe but all the best ones still used chambered heads !

precrossflow rules . . .like the dinosours :rofl:

I agree! Not in the ethos of the original car.

I used to run what was then the fastest non-crossflow 999 c.c. Cooper s in the UK!

Originally the car of the US driver, Ed McDonough and I gave the lump to my chum, arch Fordie and FVA/FVC engine builder, all round eccentric, ex-Lotus Klingon, Bruce Rennie to sort. After huffing and puffing and throwing stuff around his 'shop as he was wont to (Don't you just hate these prima donna engine builders until you go quicker than everyone else?), and swearing about siamesed ports and "S*****g BMC Crap, he magically transformed it!

Milled the ports right out; gummed in a block of mild steel a la downdraft MAE, and split two DCOE 45s and made up a slide throttle.

Boy! Did that jump along! The addition of a Norman Abbot beam axle was the final bit.

If I can find some time later this weekend (probably next week!) I'll scan a pic or two.