If you want more power from your 1988–1998 GMT400 without a full LS swap, upgrading from the 5.7 TBI to the Vortec 350 (L31) is a popular intermediate step. Here’s how it works.
Why Swap to Vortec Instead of Going Full LS?
- Less expensive than an LS swap
- Uses the same basic block and bolt pattern
- Keeps the engine family familiar (same SBC design)
- Vortec heads flow significantly better than TBI-era heads
- Perfect for trucks where you want more power but not a full conversion
What Is the Vortec 350?
The Vortec 5700 L31 was used in 1996–2002 GMT400 and early GMT800 trucks. It features:
- Vortec cylinder heads (much better flow than older SBC heads)
- Sequential port fuel injection (MPFI vs TBI)
- Better combustion chamber design for more efficiency
- ~250 HP vs ~210 HP for the TBI 350
What’s Needed:
- L31 Vortec engine (from 1996–2002 truck)
- Intake manifold must match Vortec heads (different port design)
- Vortec ECM and wiring harness (MPFI system)
- Fuel system upgrade (MPFI requires higher fuel pressure than TBI)
Can I Put Vortec Heads on My TBI Block?
Yes! Vortec heads bolt onto pre-1996 SBC blocks with some modifications:
- Intake manifold must be Vortec-spec (EGR compatible)
- Pushrod length may need adjustment
- Head gaskets must match Vortec combustion chamber design
Power Gains:
Head swap only (TBI block + Vortec heads + Vortec intake): ~30–40 HP over stock TBI setup
Alternative: Skip the Vortec, Go LS
For maximum long-term performance, the LS swap delivers more power, better reliability, and better parts availability. The Vortec swap is a good middle-ground for original-style trucks.
Have you done a Vortec swap or head upgrade on your GMT400? Share your experience!