1. Of a motor, to increase very quickly or suddenly in rotational speed; to rev up. ("Tach," pronounced "tack," is a shortening of "tachometer," an instrument used to measure rotations per minute.) Every night, at exactly 2 AM, I hear the sound of motorcycles taching up outside my house. The motor started making an awful grinding noise as it tached up to 6200 RPMs.
2. To increase the revolutions per minute of a motor, especially very quickly or suddenly. In this usage, a noun or pronoun can be used between "tach" and "up." The driver beside me started taching up his engine while we waited for the light to turn green, egging me on to engage with him in a road race. Don't tach the motor up like that—it's really disturbing for everyone who lives in this neighborhood.
See also: up
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.