The Ladder

Build phases, explained.

GMMG offered every model in a phased package structure. A Phase I Berger SS and a Phase I Blackbird share the same core parts list. What changes above Phase II is where each model line diverges — and how the ZL-1 Super Car got to 627 hp.

  • I

    Phase I — Bolt-on

    Whisper cold-air intake · ported MAF housing · ASP underdrive pulleys · ported factory exhaust manifolds · custom chambered exhaust · LS1 Edit tune. Reliable, warranty-safe, still walks a stock LS1.

    380–400 hp
  • II

    Phase II — Heads / cam / headers

    Long-tube headers · catted Y-pipe · ported LS6-spec heads · custom camshaft · hardened pushrods · ported throttle body. Hot Rod Edition Phase II dyno'd at 435 hp at the flywheel. This is the workhorse phase.

    435–475 hp
  • III

    Phase III — Displacement

    Available on ZL-1 Super Car and Dick Harrell WBE only. 427ci LS-based short block · upgraded valvetrain · GMMG-specific tune. Where GMMG stops modifying the LS1 and starts building an engine.

    550–600 hp
  • IV

    Phase IV / SR427 — GM Racing 427

    All-aluminum 427ci LS crate motor derived from GM Racing's C5R Corvette race program. Full-flow oiling, forged internals, GMMG-specific tune. This is what a Phase IV ZL-1 Super Car actually is.

    627 hp
  • V

    Phase 5XR — Race-only

    Dick Harrell drag/prototype cars only. 454ci LS variant. Not street-legal, not registry-tracked as production, but documented for provenance completeness.

    680 hp
Shared Chassis

What every phase shares.

Regardless of phase, every GMMG-built F-body received a common chassis package. This is what separates a real GMMG car from a Phase-I-looking modified SS.

Base platform2000–2002 Camaro SS or 2001–2002 Trans Am WS6
ChassisB4C police-package subframe, stiffer bushings, HD cooling
BrakesZ06-spec 12.8-inch slotted rotors; upgraded pads on Phase II+
SuspensionPenske double-adjustable nitrogen shocks (Phase III+ standard)
Rear axleFord 9-inch conversion (Strange Engineering) on Phase III+
InteriorNumbered dash plaque · Matt Murphy signed door-jamb tag
Engine bayGMMG plaque riveted to passenger-side inner fender
OptionsCoupe / T-top / convertible · 6-speed manual or 4L60E automatic
See phases by model → How to verify