The paper trail on General Motors’ next-generation V8 program just got a lot more interesting. GM-Trucks.com has learned that RPO codes for the new Gen 6 Small Block V8 family have surfaced in GM’s dealer network, along with a brand new factory oil specification for the engines that will power the 2027 Chevrolet Silverado 1500 and 2027 GMC Sierra 1500.
According to information provided to us by a trusted source, the two Gen 6 V8 RPO codes are L76 and L78. At the same time, a new 0W-30 engine oil certified to GM’s dexos1 Gen 3 standard came across the dealer ordering wire this week, available in quarts, 55 gallon drums, and bulk delivery so service departments can stock up before the new trucks arrive.
Two New RPO Codes: L76 and L78
When General Motors gave us our official first look at the 2027 Chevrolet Silverado, the company confirmed two new naturally aspirated Gen 6 Small Block V8s, a 5.7L and a 6.6L, but stopped short of releasing output figures or engine codes. Now we have the codes.
GM has not yet confirmed which code belongs to which displacement. Based on how GM has numbered its V8 families for decades, our read is that the smaller number goes with the smaller engine. Here is how the Gen 6 V8 lineup shapes up:
| RPO Code | Engine | Transmission | Factory Oil |
|---|---|---|---|
| L76 | 5.7L Gen 6 Small Block V8, naturally aspirated | 10-speed automatic | 0W-30 dexos1 Gen 3 |
| L78 | 6.6L Gen 6 Small Block V8, naturally aspirated | 10-speed automatic | 0W-30 dexos1 Gen 3 |
That pattern holds today: in the current trucks, the 5.3L V8 carries the L84 code while the bigger 6.2L is the L87. Ascending number, ascending displacement. We would be surprised if GM broke that convention now.
If those two codes ring a bell for longtime Chevy fans, they should. L76 was the RPO for the solid-lifter 327 cubic inch small block that made 365 horsepower in the mid-1960s Corvette, and it returned in the 2000s on a 6.0L Gen IV V8. L78 is even more famous: it was the 375 horsepower 396 big block that turned Chevelles and Novas into legends. Reviving both codes for the most powerful naturally aspirated V8 family in the class feels very intentional.
A New Factory Oil: 0W-30 dexos1 Gen 3
The second piece of news is one every future owner will live with at every oil change. The Gen 6 V8s are moving to a 0W-30 viscosity oil under GM’s dexos1 Gen 3 specification.
Here is the important context: dexos1 Gen 3 is the same certification standard behind the 0W-20 and 5W-30 oils that today’s Silverado and Sierra gas engines already use. In other words, the specification generation is not changing. What changes is the viscosity grade GM is pairing with the new V8s.
Compared to the 0W-20 that the current 5.3L and 6.2L V8s call for, a 0W-30 keeps the same easy cold-start flow (that is the 0W part) while holding a thicker, more protective oil film once the engine is fully warmed up and working hard. For a naturally aspirated V8 family that GM says will be the most powerful in its class, and one that will spend its life towing and hauling, prioritizing hot film strength makes a lot of sense. Consider that our analysis rather than an official GM explanation, but it lines up with where high-output engines across the industry have been heading.
To be clear, nothing changes for current owners. If your truck calls for 0W-20/OW-40 or 5W-30 today, keep using it. The 0W-30 is for the new Gen 6 engines.
What Dealer Stocking Tells Us About Timing
Fluids showing up in the dealer ordering system in quarts, drums, and bulk is not a small detail. It is one of the later steps in launch preparation, the point where GM wants every service department physically ready to maintain the new engines before customer trucks hit the road.
That tracks with everything else we know. Silverado production begins later in 2026, and as we covered in our deep dive on the next-gen 2027 GMC Sierra 1500, retail trucks are expected in driveways before the end of the year. Expect official output figures, and confirmation of which RPO code belongs to which V8, in the months ahead. When it happens, you will read it here.
Join the Discussion
What do you think GM has in store for the L76 and L78? Jump into the Gen VI Small Block V8 forum where members are already digging into the new engines, or talk trucks in the 2027 Silverado 1500 and Sierra 1500 forum.
Zane Merva is the Executive Editor of GM-Trucks.com and the President of the New England Motor Press Association (NEMPA). A veteran automotive journalist with over 26 years of experience, Zane is a designated ‘Car Talk’ Expert and has been a contributor to The Boston Globe. He possesses a unique evaluative perspective, having road-tested more than 2,000 vehicles across every major manufacturer. While he is a recognized authority on General Motors truck platforms—including the Silverado, Sierra, and Colorado—his expertise is grounded in decades of deep competitive analysis that few in the industry can match. His commentary has been featured by major OEMs and media outlets, including Hyundai and PR Newswire