Was there a pun in "quiet obvious"
In seeing the photos of all the variations, It seems they all have an internal Y pipe, but the non 1M cars have perforations in the collector to allow resonances to dissipate into the wool, whereas the 1M has the same Y pipe without perforations. The question is whether allowing the resonances to be absorbed into the wool actually limits power in any way. It seems to me that it would be effective at reducing resonance (drone) but not rob power.