I have the same question.
My MC21 has the HRC Delimiter (= wire splice), the air box is fitted and there are no holes drilled into the lid. The bike pulls strongly to 12,000 RPM in top gear (and beyond, I chickened out around 12,200 on a very gradual downhill 'aerodrome'). I weigh 80 kg. It doesn't feel at all strangled up there. Hence wondering what the gains would be by drilling holes in the lid?
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Rich
MC21 Track Bike / RS250 NF5 'Spencer', NX5 'Cadalora' & NXA 'Aoyama' / RS500 / Two Brothers Racing RC30