What Are The Custom OS's & Their Differences?

1 Bar MAF Custom OS

• Available For: Most 99+ LS1-based PCMs.
• Features:
  • Adds Real-Time Tuning (RTT) to the stock calibration.

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1 Bar Speed Density (SD) Custom OS

• Available For: Most 99+ LS1-based PCMs.
• Features:
  • Adds a VE Multiplier vs. TPS vs. RPM table.
  • Disables secondary VE table (if applicable).
  • Speed Density mode only.
  • Supports High and Low Octane Spark tables.
  • Includes RTT (most calibrations).

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2 Bar Speed Density (SD) Custom OS

• Available For: Most 97-07+ LS1-based PCMs.
• Features:
  • 2-bar MAP sensor support (calibrates for GM 0–5V linear MAP sensors).
  • Extends Main VE table to 210 kPa (2 bar).
  • Retains 5 kPa resolution in non-boost and boost regions (most calibrations).
  • Adds Boost Enrich and open-loop MAP threshold tables.
  • Disables secondary VE table (if applicable).
  • Supports High and Low Octane Spark tables.
  • Speed Density mode only.
  • Adds RTT and new MAP PID for VCM Scanner (if applicable).

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3 Bar Speed Density (SD) Custom OS

• Available For: Most 99+ LS1-based PCMs.
• Features:
  • 3-bar MAP sensor support (calibrates for GM 0–5V linear MAP sensors).
  • Extends Main VE table to 315 kPa (3 bar).
  • Retains 5 kPa resolution in non-boost and boost regions (most calibrations).
  • Adds Boost Enrich and open-loop MAP threshold tables.
  • Disables secondary VE table (if applicable).
  • Supports High and Low Octane Spark tables.
  • Speed Density mode only.
  • Adds RTT and new MAP PID for VCM Scanner (if applicable).

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2.5 Bar MAP - Speed Density (LS2 V8, E40 ECM)

• Features:
  • 2–2.5 bar MAP sensor support (calibrates for GM 0–5V linear MAP sensors).
  • Adds new Boost VE table (105–255 kPa).
  • Retains stock VE table resolution in non-boost regions.
  • Provides better-than-5 kPa resolution in boost regions (105–255 kPa).
  • Adds Boost Enrich table and MAP threshold.
  • Speed Density mode only.
  • Rescales fan temperature axis (163–250°F, 73–121°C).
  • Includes VCM Scanner histogram for Boost VE table.

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2.5 Bar MAP - Speed Density (E38/E67 ECM)

• Features:
  • 2.5-bar MAP sensor support (255 kPa).
  • Rescales High MAF table (up to 15,400 Hz and 1024 g/sec airflow).
  • Adds new VE tables (33x33 resolution with configurable MAP and RPM axes).
  • Adds TPS-based VE multiplier table (33x17 cells).
  • Supports both MAF and Speed Density mode.
  • Adds Boost Enrich tables and fuel cut based on MAP thresholds.
  • Rescales fan temperature axis (163–250°F, 73–121°C).

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Should I Use a 2 or 3 Bar Custom OS on a Naturally Aspirated Engine?

In most cases, no. For naturally aspirated engines, the 1 Bar SD Custom OS provides significant benefits:

• Removes the secondary VE table.
• Adds RTT for most calibrations.
• Retains high/low octane table functionality.
• Includes a TPS vs. RPM multiplier.

While a 2 Bar SD Custom OS offers slightly higher resolution on the primary VE table, it usually isn’t worth the additional time and effort for naturally aspirated setups.