18 replies to this topic

[Ethel]

Comparing the cam profiles may give you the answer. Maximum power is only about the top end of the rev range, the MG cam could give a wider power band with more torque and better acceleration but lose out in bhp to the Cooper if it has more duration to rev higher. The Cooper was more of a competition oriented car (and lighter) with a higher ratio final drive so it could sacrifice a little torque.

Regarding 15 years of development, not all changes were beneficial to performance. The S's head was a step too far with cracking problems between the valves, later heads are "tamed" a bit for reliability. Environmental & cost issues over production have lead to lower grade cranks, that are heavier to compensate.

Stringing together BMCEcosse's replies - if you opt for higher ratio rockers then you should consider reducing the valve spring rate by the same proportion. It's the extra leverage that magnifies the spring's force and causes wear, it also means you can get the valves up to the same rpm with proportionally less spring pressure. Done properly it's another advantage to high ratio rockers. Alternatively, it means you can extend the rev limit of standard springs with bigger rockers alone.

[cooperrodeo]

Personally I always thought 76bhp was a bit optimistic for a standard Cooper S. In the 1960s they (Jaguar in particular) measured bhp without all the ancilliaries attached and got higher figures than would be measured today.

Discuss.

[Cooperman]

There were 2 measurement standards used, 'DIN' and 'SAE'. It was suggested that SAE stands for 'Standard American Exaggerated' as it was for an engine running without dynamo, water pump or fan. Which BMC used I can't remember, but the MG should be 'DIN'.
As for the difference between 'S' and MG Metro it may be in the measuring techniques used. What is also odd is that the Innocenti Mini-Cooper 1300 has the same head and cam as the 'S' with the same CR, same twin HS2 carbs, same exhaust, etc, yet it is quoted at 71 bhp.
Personally I think in the 'S'/MG Metro case it's the cam and, possibly the carbs which make the difference, but the higher CR of the MG should make that engine slightly better. Checkn out the max torque figures and see how they compare (don't have them to hand at the moment).

[Pigeonto]

Some valid points there, from all, I fell into that old bhp trap too-forgetting for a moment that torque is far more important for acceleration. And yes,quite, how is it measured,fan,charging unit,water pump etc all add up. Any one put a MG cam into an S ? Ultimately then there shouldnt be more than a molygrott between the 2 in real terms.