Apologies, Heinrich - the explanations given above are correct ... wrinkly reversion to non-metric currency !!
Re. the smoke
from the exhaust, early Lynx at Boscombe doing pitch over for speed runs used to exhibit mini versions, and one of our Whirlwinds, coming in from Valley to TH with an uncoupled (accidental) throttle linkage produced a similar, but more flame containing example !
