Green’s Dictionary of Slang

1. a burst of speed.

1890		Polytechnic Mag. 13 Mar. 5/1: An impromptu scorch was started by trying to keep behind a really fast cabby to obtain shelter from the wind [F&H].
1901		W.A. Sun. Times (Perth) 6 Oct. 1/1: The police might endeavor to bag a few of the cyclists who habitually ride the William-street bridge [...] the favorite time for the risky scorch is when the school children crowd the structures.
1906		Queenslander (Brisbane) 24 Mar. 42/4: The motor had reached a nice level stretch of road, and the man in goggles was preparing for a scorch.

2. (UK Und.) arson.

1989

J. Morton Lowspeak.