I am new to this forum, which is why I have only just seen this thread, more than a year late. But assuming that most, if not all, of those who participated, are still active members, I would like to add something more, which they might find interesting.
What I find really different is the exhaust system of that V12 Matra; I don’t know of any other like it.
The others, whether straight-6, V12 or Flat-12, all follow much the same system: Headers from cylinders 1, 2 and 3 blend into one pipe, and the same with cylinders 4, 5 and 6. (If you regard each bank of the 12s as an independent straight-6). This may be simply explained as follows:
While the theoretical four-stroke cycle opens the exhaust valve for 180 degrees only, (during the exhaust stroke), in actual practice the valve remains open for anything between 210 and 240 degrees; opening before the power stroke ends, and closing after the induction stroke starts. Clearly, the entire pipe, from exhaust valve right up to the end, is pressurised to some extent during this period (the highest pressure being when the valve opens, falling rapidly thereafter, down to atmospheric at some point in time).
For reasons of good balance (for which the straight-6 is justly renowned), the firing order is always 1-5-3-6-2-4, with the crank throws arranged successively at 120 degrees, (to smooth out the torque as much as possible). This ensures that the firing interval between any two successive cylinders is 120 degrees of crankshaft rotation.
From the firing order above, it is clear that cylinders 1-3-2, in that order, are separated by 240 degrees each, so too cylinders 5-6-4. And now it should also be clear that that the usual arrangement of the headers (as described above) ensures that each tailpipe carries the exhaust from one cylinder only, at any time. No interference of one exhaust pulse with another, and hence free flow at all times, with only the resistance of the piping to overcome. Hence the smallest possible loss of power from this cause.
What about the Matra? They were deadly serious competitors, just like everyone else, so it is probably only legend that their six-times-two-into-one system was intended to produce the best possible sound. There must have been sound technical logic at work, (maybe known only to the designer), even if it proved fruitless in the end. Nothing unusual about that outcome in engineering, for countless reasons.
It might help if anyone knows what the exact arrangement was. Which is to say, which two cylinders were connected to each of those three tail pipes, on either bank?