Yeah, the Arbath of that era stretched the 600 to 650 and put it in the 500 bodyshell. Bore it any bigger and you were left with assorted large washers.

In full track trim the Tempest went up to about 200 bhp naturally aspirated, petrol, and the weight down to under 10 cwt - about the equivalent of 700 to 800 bhp in the Nascar machines, pound for pound.