Cybertron is a lie.
There are no Autobots and no Decepticons. No Maximals or Predacons. The war which consumed a planet never happened. But there are still Transformers. In the mid 1980's the Agency, a group consisting of representatives of the shadow militaries of the G7 nations, developed the Mindcatcher. This device, when used on a volunteer, would digitise that person's thought patterns, memory engrams, the pathways of neurons in the brain and everything else needed to create a recording of the volunteer's mind. When the volunteer died, they were implanted into the new weapons: The Transformers. Incredibly powerful humanoid robots with the ability to disguise themselves as vehicles and objects common on Earth, though often with some modification, these machines were made capable thanks to the super-fuel known as Energon. The memory-imprint (called a Spark) would be brainwashed into believing that they were a robotic alien, sent to Earth from Cybertron. They would believe their mission was to stop the wars on Earth lest it become as bad as Cybertron.
Of course, nothing's that simple. On some minds it didn't take. They remembered their pasts and did not wish to spend eternity trapped in a body of steel, a thinking weapon dancing to the tunes of people they did not know. These Transformers banded together, taking the name "Autobot", and set out to free themselves by fighting the only thing that could kill them -- the still loyal Transformers, who were dubbed Decepticons. The Decepticons in turn believed they had to destroy the Autobots, thanks to upgrades to the memory implant that the Agency put in.
And so, the war continues.
Use the Trinity rules, with some modification. Each TF has a Size stat, from 0 (Human sized) up to 10 (Metroplex/Trypticon). Starting characters have a Size of 1 (equivalent to a car-sized alt-mode), and can buy Size for 2FP. Each point of Size adds one die to an attacker's roll to hit, and adds a Health Level (add to -1, -2, 0 in that order, and loop as needed). You have 20 points of Weapons (1FP for +1) and 8 points of Mechanisms (2FP for +1) -- special crap like wings. Base Energon is 5 (2FP for +1), and has a pool like Willpower does. A third mode costs 5FP.
Edit: Stats for vehicle modes are determined by summng Physical Attributes and Appearance, and redistributing these points.
Changed Stuff: The Strength rating is compared to other TF's. For human-scales, double the listed Strength. Drive/Pilot includes "Drive/Pilot vehicle mode of self", and this counts as an automatic Specialty. Transformers can soak Lethal damage with Stamina plus any Armour Mechanism, this counts as Vehicle class armour with a 1/2 Stamina armour add. Allegiance is from human life and determines the Ability Group as normal for Trinity (ask your ST). Concept is replaced by Function, just because. Faction replaces Order and should be simple (Autobot/Decepticon)
Weapons are built thusly: 1 point for +2 Acc/RoF (which can be split), 1 point per 1L/2B damage (Ranged), 2 points per +1L/+2B (Melee), 1 point per 15 Range, 1 point for 5 Clip, 2 points to give L damage, then 1 point for a further +1 damage add, 1 point for Manoeuvers (Full Auto costs 2 without Semi-Auto as well). The standard templates are Brawl/Melee Acc: 0, Damage: 0; Ranged Acc: 0, Damage: 0, Range 30, RoF 1, Clip 5. If a weapon can be used in more than robot mode, add half the cost again.
Mechanisms are rated 1 to 5, based on their usefulness. They cover the gamut of abilities, and a full list is beyond the scope of this. Each should be tied to an Attribute, and the dice pool is Attribute+Mechanism. Half-cost again allows access to the Mechanism in multiple Modes. Sample Mechanisms include Flight (Dexterity, needed for airborn alt-modes), Armour (Stamina, +2 Soak per dot), Pistons (Strength, adds to Might), Sleek Lines (Appearance, affects humans' initial reaction, +1 Drive in vehicle mode through aerodynamic styling), Mimicry (Manipulation, record/play back conversations & steal other's voices), Magnetism (Charisma, can connect with other computers nearby), Video Zoom (Perception, every dot allows x10 vision), Holography (Wits, allows projection of hologram doubles), Force Field (Intelligence, creates barrier Int+FF radius with FF Soak).
Transforming is automatic, but takes a turn's action. A point of Energon makes this instantaneous. Energon is also spent to boost a Physical Attribute by +1 per point spent for the duration of one action and to power some Mechanisms.
The first couple of games should be straight forward, then thrust the PCs into a battle at Mount St. Hilary in Oregon. Where the battle uncovers a crashed spacecraft. A spacecraft which contains some rather disturbingly familiar beings. Yup, for all you that don't know your G1, the PCs just stumbled upon the Ark and awoke the *real* Transformers. Hilarity is bound to ensue.