One of the most popular upgrades for 1988–1995 GMT400 trucks with TBI (Throttle Body Injection) is swapping to the Vortec heads and MPFI (Multi-Port Fuel Injection) setup used on the 1996–1998 5.7L Vortec trucks. More power, better throttle response, and improved fuel economy.
What Is the Swap?
TBI (1988–1995): 5.7L uses a single throttle body injector that sprays fuel above the intake manifold, essentially like a carb with an injector.
Vortec MPFI (1996–1998): Uses Vortec heads with improved port design, an MPFI intake manifold with a central fuel injection “spider” that delivers fuel directly to each intake port.
Result: 255 hp vs. 210 hp from the TBI — and the heads flow significantly better.
What You Need for the Swap
Parts Required
- Vortec cylinder heads (L31 “Vortec 5700”) — from a 1996–2002 truck, van, or SUV
- MPFI intake manifold — the Vortec-specific manifold with the lower-plenum spider injector design
- MPFI fuel injector spider — MPFI Central Sequential Fuel Injection Spider
- Upgraded intake manifold (optional): Edelbrock 2701 Performer Intake — aftermarket option that works with Vortec heads and improves flow over the stock piece
- Head bolts — Vortec heads use different torque-to-yield bolts, don’t reuse
- Vortec-compatible distributor — check 0-ring seal compatibility; 1-wire and 2-wire versions exist
- ECM/PCM compatibility — If using factory Vortec electronics, you need the 1996+ PCM
Optional (Recommended)
- Vortec Throttle Body (matches the larger Vortec plenum)
- Upgraded fuel injectors (stock Vortec injectors are adequate for most builds)
- MSD or HEI distributor upgrade
The Swap Process
- Drain the cooling system and remove TBI intake and heads
- Clean the block deck surface thoroughly
- Install the Vortec heads with new head gaskets (use Fel-Pro for Vortec) and new head bolts
- Install the Vortec MPFI intake with a new gasket set
- Install the MPFI spider injector and connect fuel lines
- Swap the throttle body and IAC
- Connect vacuum lines — Vortec has slightly different routing
- ECM: If using the stock TBI ECM, you’ll need a tune or chip to run the MPFI correctly; 1996+ PCM swap is cleaner
Expected Results
| Spec | TBI (L05) | Vortec (L31) |
|---|---|---|
| Horsepower | ~210 hp | ~255 hp |
| Torque | ~300 lb-ft | ~330 lb-ft |
| Compression | 8.6:1 | 9.4:1 |
Most owners report noticeably better throttle response and a 10–15% improvement in highway mileage.
Common Pitfalls
- Coolant passages: Vortec heads have slightly different coolant port locations — use the correct Vortec intake gasket set
- Valve covers: Vortec heads use a different bolt pattern than earlier SBC heads
- Pushrods: Check pushrod length after swapping heads if the engine has been rebuilt previously