1275 Cooper S BHP

[richardACS]

The generally quoted BHP for the 1275S is 76bhp - would be interested to know whether this is at the crank or the wheels?

[iain1967s]

Engine power was always dyno measured, the ‘B’ in BHP typically being a water brake bolted up to the flywheel.

A rolling road would show roughly 25% less at the wheels, depending on variable drivetrain losses - helical vs straight cut box, how hard you pump up the tyres etc etc and is then ‘corrected’ to give an estimate of BHP.

ps. I was reading the “BMC Competitions Department Secrets” book recently, and it was mentioned several times that Abingdon didn’t even have a rolling road on which to develop their “works” tuning in the early 60s. BMC engines from Coventry were built and pre-tuned by Don Moore in Cambridge, then sent to Abingdon for installation into the cars.

Based on the notes in Robert Young’s “Works Minis” book, it seems Abingdon had finally installed a rolling road of its own by mid 1964, and the works 1293cc minis with ported/polished heads, 11:1 comp, twin H4’s and full race 846 cam were registering around 74 BHP at the wheels, so that would be equivalent of around 100 BHP at the flywheel.

[LMM76C]

The 1275S was always quoted in magazines etc. as 72bhp. It then suddenly became 76bhp. As far as I know that reflects the introduction of the "510" cam.

[SMOKE GREY]

The 1275S was always quoted in magazines etc. as 72bhp. It then suddenly became 76bhp. As far as I know that reflects the introduction of the "510" cam.

Never seen 72bhp quoted for a 1275S anywhere. 75 or 76 according to BMC.

[iain1967s]

The 1275S was always quoted in magazines etc. as 72bhp. It then suddenly became 76bhp. As far as I know that reflects the introduction of the "510" cam.

1966 USA brochure listed 75 ‘standard b.h.p.’ (78 gross) at 5800 rpm.
http://www.minipassionmini.50megs.com/p ... 201966.pdf

1966 UK brochure listed 76 ‘standard b.h.p.’ (78 gross) at 6000 rpm.
http://www.minipassionmini.50megs.com/p ... 65%20j.pdf

Aug 1964 Autocar review lists 76 b.h.p at 5900 r.p.m.
http://mk1-performance-conversions.co.u ... review.pdf

[LMM76C]

ALL adverts/roadtests etc. quoted 72bhp (at the time when all 3 capacities were listed to buy in the main magazines).
I recall being confused when it became 76, as the 510 cam was not common knowledge then.
Anyone suggesting otherwise is not old enough...

[SMOKE GREY]

ALL adverts/roadtests etc. quoted 72bhp (at the time when all 3 capacities were listed to buy in the main magazines).
I recall being confused when it became 76, as the 510 cam was not common knowledge then.
Anyone suggesting otherwise is not old enough...

IMG_8757 (1).jpg

Bill Boddy , Motorsport magazine March 1964 test day.

[JohnA]

This has been discussed on here before in September 2014
Cooper S performance page 3
SAE and DIN horse power differences

[iain1967s]

Thanks, John. Can you post a link to that discussion please? I can’t find it using the forum search.

I can see how 76 DIN (net) for UK, 75 SAE (net) for USA, and 78 (gross) are just conversion equivalents - with gross being measured without fan/dynamo/water pump/exhaust etc. fitted on the test stand, and net being the actual flywheel figure minus those ancillary component losses.

But that doesn’t explain where the 72 number comes from? Both of the 1964 reviews posted above quote 75 / 76 (net).

[LMM76C]

Motor, Autocar etc. all quoted 72 at the time in lists of all cars available for sale. I do not recall the figures for 1071 and 970 but 67 bhp rings a bell. (998 Cooper was 55 of course).

[iain1967s]

I’ve been browsing through various google searches and I found this in Motor Sport magazine, April 1964.
But it’s from a review/feature article comparing the three ‘S’ versions, not a general list of cars for sale.

[iain1967s]

Possibly the earliest public reference to 1275 S specs? Mid March 1964 photo from this month’s MCR

78 PS/cv = 76 BHP

[LuisM]

Don’t know about the 76BHP quote , but 175 Kph sounds a bit optimistic for a stock S engine , that would mean 7000 Rpm on a straight .