Fusion Engine - XXL
The Extra-Extralight Fusion Engine, also known as XXL or Double XL engine, is an advanced and experimental Fusion Engine type.
Since the revolutionary development of the XL Engine back in the original Star League era, engineers have continued to try and push the envelope in further reducing the overall weight of a fusion engine, with the ongoing conflict between the Inner Sphere and Clans powers providing further impetus to such efforts.
The XXL engine is the present result of such efforts, and weighs one-third as much as a standard fusion engine, but with some significant drawbacks in its present form. The XXL's light but bulky shielding technology takes up twice the space in side torso sections as a Inner Sphere or Clan XL engine of similar output, is five times as expensive as a comparable XL engine, and - most crippling - produces greatly increased heat. Shaving the engine shielding down to the bare minimum for safe operation, the XXL engine produces waste heat even standing still, and doubling the amount of heat for the use of a 'Mech's movement systems.
- Maximum Tech, p. 58