Gas Gas 4-Stroke

• Revolutionary single-cylinder 4-stroke, 350cc sidevalve engine
• Liquid cooled
• Battery-less Kokusan ignition and fuel injection systems.
• The clutch, gearbox, suspension, and brakes are proven TXT PRO items.
• Engine lubrication is by wet sump.

All these characteristics result in a light and very compact engine, very much in line with the acclaimed TXT PRO.

The frame is the new '09 tube profile in Cr-Mo alloy. The fuel tank is specific for this model. The new bike boasts a weight of 67.5 kg, also in line with the new TXT range for 2009.

Hugues Brunault:
“We didn’t want to make a 4-stroke engine, but the best 4-stroke engine”

The 4-stroke engine project for a GAS GAS trial bike came in 1998 and almost a decade has passed since then, but in this period of time they have achieved the creation, according to the company’s philosophy, of“the simplest but most reliable product, the lightest and most powerful, and at the same time the most affordable one. These were the premises we always had in mind, as well as the one we imposed on ourselves when
we conceived the engine: in GAS GAS we didn’t want to make any 4-stroke engine, but the best possible 4-stroke engine,” states Hugues Brunault, the person in charge of developing the trial 4-stroke GG bikes.

“A 4-stroke bike has its pros and cons. Among the pros we have better traction, power and a more linear torque curve, which means a more regular power delivery. In the cons we have the weight, an aspect which is minimised as much as possible in each of the products in GAS GAS. In this new engine we have put the valves at the sides of the cylinder, so that they are parallel, which lowers the centre of gravity and enables the engine to have almost the same size as a 2-stroke, also saving some weight. At the same time, this engine is much simpler in its structure, because it has fewer pieces than a conventional one,” says Hugues.

Although the great revolution in this four-stroke GAS GAS is the side-valve collocation, we cannot forget the battery-less electronic injection system, a complete premiere that will also be applied shortly to the new 4-stroke 250 that is already being prepared.

GAS GAS started their 4-stroke production in the enduro field. The first engine built by the company was a 400cc which would grow up to 450cc within two years. In 2005, a new generation of 4-stroke GAS GAS appeared, always with electronic injection to guarantee an increase, with some future evolutions, of the engine power and performance, a good compromise that has
seen its technology transferred to trial.

Hugues Brunault explains: “The 4T engines have about twice as many parts as similar-sized 2-strokes. On the other hand, the manufacturing process for each part is much more precise
and controlled.” The resulting bike has already been tested by Jordi Tarrés with very high reliability results. The manufacturer’s intention is to make its debut before the end of the year, although initially the bike used will be a standard model.

Jon Stoodley
Trials Engine Design

An analysis of the Gas Gas 4-stroke and
side-valve engines in general.

First printed in
Trials & Enduro News

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Videos of the 4-stroke