If I remember correctly, Vance was attempting
a record in the 3,000cc class, where the record
was substantially lower than in his
"basic" class of 2000cc.
He was unable to enlarge his engine beyond
about 1750cc, and so unable to "reach"
his preferred class of 3,000cc.
He also needed to run in a blown class.
Ever thoughtful, Vance added a "blower" which
was powered by a 300cc rope-start auxiliary engine.
(Think: leaf blower )
The SCTA rightfully adds the displacement of both engines together,
so Vance was moved up to the 3,000cc class, and to blown.
Vance would "rope start" the auxiliary engine on the start line,
and fire the Nitro motor next, and off he would go.
I think there was some question if the auxiliary engine
continued to run - and drive the blower -throughout the 289mph run.
Some said that auxiliary engine was "cold" after the run.
If the auxiliary engine was NOT running, than
the bike would not be legal for the class.
Still, the bike ran 289mph.
But, was it Blown ?