L8T 6.6L engine: specs, donor vehicles & swap notes
The L8T is a 6.6 L iron-block Generation V engine built 2020–2026, rated 350–401 hp. It came in 4 vehicle applications, including Chevrolet Silverado HD/GMC Sierra HD, Crate engine. Things to know: it has variable valve timing; it is direct-injected (Gen V parts and controller).
| Spec | Value |
|---|---|
| RPO | L8T |
| Family | Generation V |
| Years | 2020–2026 |
| Displacement | 6.6 L / 401 ci |
| Horsepower | 350–401 hp |
| Torque | 425–464 lb-ft |
| Bore × stroke | 4.065 × 3.858 in |
| Compression | 10.80:1 |
| Block | iron |
| AFM/DOD | No |
| VIN 8th digit | 7 |
| Reluctor | 58x |
| Throttle | Drive-by-wire |
| Stock cam | 0.549 in lift, 218° int / 231° exh duration (LT2-derived) |
| Computer | Global B (HP Tuners' computer unlock first) |
We tune and review logs for the L8T
Gen V LT on HP Tuners. Send your Global B .hpt after you have bought HP Tuners' ECM/TCM unlock. The free Tune Report tells you what to fix first, in plain English, within 1 business day of getting your file. Full Custom is built from your logs.
Free Tune Report Full Custom from $199
LT reports use the same format as the LS sample. The free turn-on values are LS swap tools only; LT owners start with the Tune Report or Full Custom.
- Excessive oil consumption (up to 1 qt/1000 miles). Fix: Check oil level regularly and keep topped off; use 5W-30 full synthetic; change oil more often when towing.
- Exhaust manifold gasket leaks. Fix: Replace the exhaust manifold gasket.
- Knock sensor failure (P0325). Fix: Replace the faulty knock sensor; it is an inexpensive, DIY-friendly repair.
- Timing chain stretch from low oil. Fix: Keep oil level full at all times; replace stretched timing chain if it jumps teeth.
For 2027 the heavy-duty trucks move to the L8S. See what GM has confirmed about it so far.
Iron/Alum. heads, VVT, DI
The L8T specs above are not yet confirmed against GM documents; GM ratings varied by year and vehicle.
Swapping the L8T: what to plan for
- Computer: the L8T is a Gen V direct-injection engine, so it needs a Gen V computer or a Gen V-specific aftermarket kit; Gen III/IV harnesses and computers don't run it. More: LS swap ECU comparison.
- Drive-by-wire throttle: plan on the pedal and throttle body that match the L8T and its computer.
Refresh parts for the L8T
Our Gen V refresh list was checked for the 5.3 L and 6.2 L Gen V engines. Head gaskets, head bolts and sensors on the L8T can differ, so we don't pick parts for it here: confirm each part number fits before you buy. The list is in one place: refresh while it's out.
Donor vehicles with the L8T
Where to find an L8T at the junkyard: 4 vehicle applications below. Confirm it from the RPO sticker in the glovebox or the 8th VIN digit (for the L8T: 7).
| Vehicle | Years |
|---|---|
| Chevrolet Express/GMC Savana 2500/3500/4500 | 2021–present |
| Chevrolet Low Cab Forward 3500 HG/4500 HG/5500 HG/5500 XG | 2021–present |
| Chevrolet Silverado HD/GMC Sierra HD | 2020–2026 |
| Crate engine | 2023–present |