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!
For the Obrizok 455, we started off with EFI Live's OS3 speed density setup. The car doesn't employ nitrous, so we didn't need OS4, and the build wasn't radical enough to warrant the ALPHA-N tuning of OS5. To initially convert to a custom EFI Live operating system, a defined ritual of read and full re-flash is required; the entire process is detailed in EFI Live's help files, step-by-step. Once the tune is opened in the editor, a new box appears under the calibration window: EFI Live Custom Calibrations. Within this new section are all the 'special' maps included with each custom operating system. We weren't running boost, but the shown map is of the "boost VE table." | 
One of the first orders of business when switching to speed density is to bump up the fuel delivery mapping to a safe level. It's always better to tune from rich to lean. Based on our experience with big-cube LS1s we went ahead and cranked up the entire main VE table by at least 25 percent in some sections--and by even more up top. It should be noted that all other relevant parameters must be adjusted first too. For instance, if larger injectors are installed, the injector tables must be corrected before getting started. It's important to 'correct' everything before 'tuning', otherwise you'll be tuning around incorrect parameters. | 
Speed density operation requires definition of a commanded fuel table (B3647). This is where to set the desired AFR for each operating point, (rpm vs MAP). Generally speaking, the naturally aspirated LS1 makes peak power around a 12.95 AFR. These engines are happy to cruise at a 14.7 AFR. Now, idle and low-speeds are somewhat tricky. First, the measured AFR in the exhaust at these low speeds may not be entirely representative of the combustion process--thanks to aggressive cam overlaps. So this low speed area will likely require some experimentation to find out which 'target AFR' makes the engine behave best. Standard convention would make you think that 14.7 is the best. Rarely is this true. Mistakes in this area are typically evident when a car 'bucks' and 'stumbles' at low speeds. This is where lousy or amateur tuners usually fall on their faces. Prepare yourself and be patient with this. |
Before starting any tuning, a backup of the original tune should be saved. This backup can be used by EFI Live to summarize all the changes made to a file. EFI Live has a convenient 'comparison summary' that shows all differences (or similarities) between two files. It's a good idea to double check this summary prior to flashing a file--just to make sure everything you 'think' you did, was successfully saved. | 
After setting up a tune file for speed density, the EFI Live scan tool needs to be configured as well. The shown activated PID (parameter identifier) list is a good starting point, listing the basics needed for speed density data logging. The scanner first must be configured to read and capture the external wideband signal, as delivered by our FAST meter. The FAST meter output works with EFI Live's pre-configured PID: "AFR-LM1," and the corresponding ratio of "measured AFR/commanded AFR," known as the "Base Efficiency Numerator--LM1" (BEN) PID. | 
The data screen (F9) in EFI Live's scanner offers a quick and convenient way to check in on all captured PIDs. It's a good idea to watch this page while scanning for the first time to make sure everything you want to capture is being scanned and producing realistic data. If the wideband setup was botched, you'll notice the problem here first. |