The LBZ and LMM Duramax share the same basic turbo setup — a variable geometry turbocharger (VGT) that controls boost through movable vanes. The factory turbo is good, but it’s a limiting factor once you start pushing serious power through tunes and fueling mods.
FACTORY TURBO LIMITATIONS
- Factory VGT can support 400–450 rwhp in good condition
- Above 400 rwhp the compressor wheel starts to surge under load
- VGT vanes wear and stick on high-mileage trucks — causes black smoke and power loss
SINGLE TURBO UPGRADES
- Stage 1: Cleaned/rebuilt VGT — good starting point if factory unit is worn
- Stage 2: Larger wheel drop-in — S300 or similar wheel in factory housing
- Stage 3: Full replacement turbo — Fleece Cheetah, Garrett GT4088R, BorgWarner S400
- Gains: 30–50 rwhp over stock with a supporting tune
COMPOUND TURBO SYSTEMS
- Two turbos in series — smaller charger feeds the factory turbo
- Dramatic improvement in spool time and EGT control under load
- Gains: 150–250+ rwhp depending on setup and fuel
- Fleece Performance compound kits are the most popular option
WHAT YOU NEED TO SUPPORT A TURBO UPGRADE
- Professional tune from EFI Live or Autocal
- Upgraded intercooler — factory unit becomes restrictive above 400 rwhp
- Lift pump — especially on LML trucks
- EGT gauge — keep exhaust temps below 1200°F