GunBir-O is the second major combining robo of "Engine Sentai Go-onger" and the primary mecha of the Go-On Black and Go-On Green Rangers. It forms from three Engines (the series' living vehicle partners): Gunpherd, Go-On Black's dog-like police-car Engine; Birca, Go-On Green's swordfish motorcycle Engine; and the mighty alligator carrier Engine Carrigator, which serves as the base, legs and torso. The name "GunBir" is a portmanteau of Gunpherd and Birca plus their signature speech quirks ("Ganga gan" and "Baru baruka") - a charming touch that captures the playful personality of the Go-onger Engines.

Where the first robo Engine-O is grounded and sturdy, GunBir-O is the team's aggressive close-quarters fighter. Carrigator's distinctive alligator head sits proudly on the chest, while Gunpherd and Birca form the arms and upper body. Its finisher, the "Gunpherd Gun" barrage, unleashes an energy-bullet assault, and swapping in partial combinations (such as GunBir-O Toripter with one of the Wing Engines) changes its armament and attacks. Its greatest moment: GunBir-O docks with Engine-O to form the six-Engine Engine-O G6 - and, together with Seiku-O, it is part of the colossal Engine-O G12 that unites all twelve Engines, one of the most spectacular gattai configurations in Sentai history.

The DX toy "DX Engine Gattai GunBir-Oh" was released by Bandai Japan on 26 April 2008. The set includes all three Engines - Gunpherd, Birca and Carrigator - each with its inserted "Engine Soul" (the small soul module that "awakens" the Engines in play). The centerpiece of the gimmicks is compatibility with the DX Go-Phone: entering the combination code 5*6 lets you connect GunBir-O with the separately sold DX Engine-O to build Engine-O G6 (and onward to G12). The figure features light and sound effects, a firing action, and the classically solid, click-together DX construction.

For the Western market Go-onger was adapted as "Power Rangers RPM," where GunBir-O appears as the ValveMax Megazord, released by Bandai America as its own zord. In Japan, special runs followed over the years, including the recolored "Police Deco" GunBir-Oh and a Mini-Pla model-kit candy-toy version - must-haves for any complete Go-onger display shelf.