The General's Gen III engine architecture turns ten years old in 2007. Unlike most 10-year-olds in this industry, the Gen III engine appears to keep getting 'hotter' as it ages. It's safe to say, the Gen III engine (DBA the "LS1" or "LSx") has established itself as 'the' small block engine of today. There's really one key requisite for an engine to reach the throne--ability to make sick power. With that being the case, the LS1 has it all over its Big Three counterparts.
Pushing the envelope of Gen III engines used to be held up by limitations inherent to the factory powertrain control module (PCM). Factory PCMs employ an operating system (control strategy) designed to control engines with steady and smooth low-speed characteristics, consistently representative exhaust compositions, and mass-airflow (MAF) friendly naturally aspirated (1 bar) induction systems. Stock LS1 operating systems (OS) also have fuel economy, emissions, and longevity prioritized ahead of performance. None of these operating characteristics or priority objectives are typical attributes of push-the-limit, bad-ass Gen III engine builds. Huge cam manifold pressure (MAP) characteristics are generally quite rude, and especially unstable at low speeds. Also with big-cam engines, the exhaust composition inside a header collector, three feet from the valves, is nothing but potluck during idle and low speeds. The intake side of big-cam engines suffers from the same instabilities, often sending low-speed MAF signals into a chaotic frenzy.
Early attempts to make wild engines behave under factory PCM control involved tricking them into MAF-less "quasi-speed density" and usually permanent open-loop operation. The PCM was effectively locked into its default MAF failure limp mode, and the fuel delivery command table was modified to serve as the main fuel lookup table. This trickery falls victim to various caveats, one being the elimination of dual spark maps (high and low octane). While functional, this operation also poses serious limitations in how accurately an engine can be controlled. Primarily, fuel delivery is tuned only by MAP and ECT (engine coolant temp)--no rpm or throttle position (Alpha-N) consideration is used to command fuel. Once tuned to deliver the desired fuel, this configuration can be run in closed loop, but without rpm or throttle position input, idle and low speed typically remained ill-behaved. This setup also did nothing to enable boosted engine mapping or help control nitrous-demanded spark retard.
But don't ditch that factory controller just yet--it didn't take long for EFI Live's Paul Blackmore and Ross Myers to realize the need to overcome the limitations of factory operating systems. EFI Live, already one of the premier Gen III tuning software pioneers, has raised the bar again with their introduction of "Custom Operating Systems." These custom systems were created (and continue to evolve) by EFI Live to improve the capabilities and expand the functionality of speed-density control for Gen III engines. Currently, five versions of the EFI Live operating systems exist, each including progressively more features to suit a particular tuner's needs:
Version 01: This is EFI Live's entry-level speed density system. With this version, the high-octane spark map and full adaptive spark control is functional, unlike the 'tricked' speed density mode (no custom EFI Live operating system) where spark is limited to the semi-limp mode low-octane table.Version 02: This version includes a trick "Valet Mode', like ZR-1s had. The PCM is reconfigured with a secondary rpm and speed limiter, programmable as desired. The Valet mode is toggled by way of a user-installed switch (or key-switch), wired directly into the PCM harness. Once the switch is activated, the vehicle is restricted to the preset 'Valet' rpm and speed limits. Valet is a cute option, but for the racers, Valet can be adapted to function as a two-step launch controller.
Version 03: Enter boost mapping. This custom operating system introduces a set of 'boost' tables to accurately tune and command fuel and spark delivery all the way up to 3 bar. And for the non-boost applications, Version 03 has merits too. The operating system remaps the open-loop commanded fuel table by replacing the ECT axis with much a more functional rpm axis. Open-loop fueling can be accurately tuned by rpm and MAP.
Version 05: Alpha-N fuel mapping is added in this version. Fuel delivery can be commanded by throttle or MAP, depending on how the tuner desires to configure it. For those with the nastiest of cams, low speed operation can be controlled exclusively by throttle, eliminating problems from erratic MAP signals. Transition to MAP-based fueling can be set for any rpm and throttle points.Sticking with the corporate GMHTP objective of covering cutting-edge GM performance, we set out to walk our readers through the setup and tuning of an EFI Live Custom Operating System. The timing was perfect, as longtime GMHTP subscribers, Bob and Jon Obrizok, just finished building a 455-cube LS1 for their 2002 WS6--complete with a spicy Thunder Racing/Comp Cams 248/248, 580/624, 112 LSA cam, and the need for a killer tune!