If you’re shopping for a GMT800 2500HD or doing an LS swap, you’ll encounter both the LQ4 and LQ9 designations. Here’s a concise breakdown of the differences.
LQ4 – The Standard 6.0L:
- 6.0L displacement
- Iron block
- Cast iron cylinder heads (same cathedral port design)
- ~300–325 HP stock (depending on year)
- Used in: Silverado 2500HD/3500HD, Express vans, various commercial trucks
- Common years: 2001–2007
LQ9 – The High-Output 6.0L:
- 6.0L displacement
- Iron block (same as LQ4)
- Upgraded aluminum heads (same as LS2 – much better flow)
- ~340–345 HP stock
- Used in: Escalade, Avalanche, some Yukon applications
- Common years: 2002–2006
The Key Difference: Cylinder Heads
The LQ9 comes with the same rectangular port heads found on the LS2 (used in the 2005–2006 Corvette and GTO). These heads are much better for making power than the cathedral port heads on the LQ4.
Why the LQ9 Is Popular for Swaps:
- You get the strength of an iron 6.0L block
- With the better-flowing LQ9/LS2 heads already installed
- Cheap to find from salvage yards
Can You Put LQ9 Heads on an LQ4 Block?
Yes! This is a popular upgrade. The LQ9/LS2 heads bolt directly onto the LQ4 block with the appropriate intake manifold.
Bottom Line:
If you’re choosing between the two for a swap or upgrade, the LQ9 is worth the small premium for the head upgrade. Otherwise, you can do a head swap from LQ9 to LQ4 later.
Do you have an LQ4 or LQ9 in your build? What power level are you at?