Re: exhausts

["John Hertzman" <johnhertzman@domain.elided>]

Responding to Alafanovice, who had written "I have seen the 'middle exhaust'
called a resonator, for what that is worth", . ian lomax wrote "i'm pretty
sure the first muffler is the resonator, not the center muffler.  most later
alfa's don't have a resonator, they have the catalyst in the same place."

I have never felt a clear understanding of the relationship of "resonators" to
"mufflers", so I decided the time had come to try harder. The desk dic, after
a detour into piezoelectric crystals, says a resonator is "a device for
increasing the resonance of a musical instrument", which I guess explains why
there would be one on an Alfa. For resonance itself, after a bit about
vibrations of large amplitude caused by relatively small periodic stimuli, it
goes into "the intensification and enrichment of a musical tone by
supplementary vibration", which again sounds entirely appropriate to Alfa but
again doesn't say why which would be what.

The English end of Cassell's doesn't list "resonator", but for 'resonant" and
"resonance" gives Italian "risonante" (or "sonoro") and "risonanza', so
resonator should be risonatore, for which I went looking.

The polyglot parts books for the last pre-cat Alfas call the big second
chamber a silencer (or silenziatore, silencieux, schalldampfer, silenciador)
and call the little first one a muffler (or polmoncino, pot de predetente,
schalldampfer vorn, or pulmon), and the other parts books back to the
Giulietta are pretty close; the Catalogo Rapido has silenziatore for the
second and polmoncino for the first, the English-only 1600 coupes book has
muffler for the first and silencer for the second, the Giulietta book calls
the front the polmoncino or baffle and the big second one the marmita or
muffler; the 1900 parts book calls the big #2 a silenziatore and calls both
the front #1 and rear #3 polmoncini.

Cassells does not include "polmoncino" but reverse-engineering from what it
does have (polmonite = pneumonia, polmonare pulmonary, polmone lung) a
polmoncino should be something like a little lumg, presumably an expansion
chamber, perhaps for damping out resonances before and after the muffling.

Whatever. Regardless, the credit for the sweet-sounding and probably very
tunable three-chambered organ pipe seems to belong to Satta, probably
expanding on sensibilities which emerged under Jano in the thirties. The only
chassis drawings and body-off chassis photos I have of the 2500 or the late
2300s (the 2300B) show a single transverse muffler behind the fuel tank, with
a long first chamber which is only slightly larger in diameter than the pipes
in and out; the chassis drawings for the first series 6C 2300 and all prior
Alfas show a single muffler (or silencer, marmite, whatever). So it was one
from 1910 to 1934, modified in or around 1934 (I'm guessing with the Pescara,
to lower back-pressure while maintaining sufficient quieting, but that is just
a guess) to have a relatively long expansion chamber? before the muffler, and
increased to have a main low-back-pressure muffler with prior and subsequent
expansion polmencini by Satta in developing the 1900 in the late forties,
laying the pattern followed by the musical Giulietta and the Giulias.

The wartime drawings for the Gazella prototype, Ricart's one passenger-car
project at Alfa, show a single transverse rear muffler with an uninterrupted
pipe from the manifold, so he seems not to have been a player.

All this is mostly guesswork, and probably of little interest to most, but if
anyone wishes to resonate a different set of vibrations out of the evidence,
have at it.

Cheers

John H.
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