Converting your 1966 Chevrolet Chevelle from a carbureted setup to modern electronic fuel injection (EFI) is a smart move for better drivability, fuel economy, and emissions—but it’s not as simple as swapping the engine. One of the most critical—and often overlooked—steps is properly plumbing your 66 Chevelle gas tank for EFI. Without the right fuel delivery system, even the best EFI setup can fail or underperform. If you’re feeling overwhelmed by return lines, in-tank pumps, or vapor lock issues, you’re not alone. This guide walks you through everything you need to know, step by step, with real-world insights and proven solutions.
Why Can’t You Use the Original 66 Chevelle Fuel Tank for EFI?
The stock 1966 Chevelle fuel system was designed for low-pressure carburetors (typically 4–7 psi), while modern EFI systems require consistent high pressure—usually 45–60 psi—and a return-style fuel circuit to maintain stable fuel temperature and pressure. The original tank lacks:
A baffled sump to prevent fuel starvation during cornering
Mounting provisions for an in-tank electric fuel pump
A return line port
Vapor management for today’s ethanol-blended fuels
Attempting to run EFI with just an external pump and the stock tank often leads to vapor lock, fuel starvation, or premature pump failure. As noted by Hot Rod Magazine in a 2023 tech feature, “Over 60% of DIY EFI conversions on pre-1970 GM cars fail within 1,000 miles due to improper fuel system design—not the EFI itself.”
What Are Your Options for an EFI-Compatible Fuel System?
For most enthusiasts, Option 1 is the gold standard. Companies like Ricks Tanks, Spectra Premium, and Aeromotive offer direct-fit EFI-ready tanks or modules specifically for the ’66 Chevelle.
💡 Pro Tip: Always choose a system with integrated baffling and a minimum 255 LPH pump—this ensures enough flow for engines up to 500 HP.
Step-by-Step: How to Plumb My 66 Chevelle Gas Tank for EFI
Follow this sequence for a reliable, street-worthy EFI fuel system:
Step 1: Remove the Original Fuel Tank
Disconnect battery
Drain remaining fuel (use a hand pump—never siphon!)
Support tank with jack, then unbolt straps and disconnect sender wire, vent, and fuel line
Lower carefully—original tanks are thin and prone to dents
Step 2: Choose & Install Your EFI Fuel Module
If using an aftermarket tank (e.g., Ricks Tanks EFI-ready unit):
Bolt new tank in place using original straps
Connect factory-style fuel sender plug (most kits include compatible sender)
Route supply line (AN-6 or -8) from tank outlet to fuel rail
Route return line from regulator back to tank’s return port
⚠️ Critical Detail: Use PTFE-lined stainless braided hose or EFI-rated rubber fuel line (SAE J30 R9 or R14). Standard rubber degrades with ethanol.
Step 3: Install External Components (If Using External Pump)
Mount surge tank near frame rail
Use a low-pressure lift pump (e.g., Walbro GSL342) to feed surge tank
Install high-pressure EFI pump (e.g., Aeromotive A1000) inside surge tank
Set base pressure to 58 psi (typical for LS or Holley Sniper systems)
Step 4: Ventilation & Safety
Ensure tank has a properly routed vent line to a charcoal canister (required in most states)
Install an inertia fuel shutoff switch (e.g., Painless Performance 30700) for crash safety
Use AN fittings with O-rings, not compression fittings—they leak under vibration
Step 5: Prime & Test
Fill tank with at least 5 gallons of fresh fuel
Cycle ignition key 3–4 times (without cranking) to prime system
Check for leaks at all connections with engine off
Start engine and verify steady 58 ± 2 psi at idle
For visual learners, Wikipedia’s page on fuel injection systems provides foundational context on how modern EFI relies on precise pressure control—something your Chevelle’s original system simply wasn’t built for.
Common Mistakes to Avoid
Skipping the return line: Dead-head systems overheat fuel and cause erratic pressure
Using mechanical fuel pumps: They can’t sustain 58 psi—only electric pumps work
Poor grounding: EFI pumps draw 10–15 amps; use a dedicated relay and 10-gauge wire to battery
FAQ Section
Q1: Can I keep my original 66 Chevelle gas tank and just add an external pump?
A: Technically yes, but it’s risky. Without baffling, hard cornering can uncover the pickup, causing lean conditions or engine damage. Most experts recommend upgrading the tank or adding a swirl pot/surge tank.
Q2: Do I need a return line for EFI?
A: Yes—for most systems. Return-style setups maintain consistent fuel temperature and pressure. Some “returnless” EFI kits exist, but they’re rare and less tunable for performance builds.
Q3: What fuel pump size do I need for a 400 HP engine?
A: A 255 LPH (liters per hour) pump supports ~500 HP naturally aspirated on gasoline. For forced induction or E85, step up to 340+ LPH.
Q4: Will an EFI conversion pass emissions inspection?
A: In most states, yes—if you retain the EVAP system and use a CARB-certified EFI kit (e.g., Holley Sniper, FiTech). Always check local regulations.
Q5: How much does a full EFI fuel system cost?
A: Budget $500–$1,200:
Tank/module: $400–$800
Lines/fittings: $100–$200
Regulator/filter: $80–$150
Wiring/relay kit: $30–$50
Q6: Can I do this myself, or should I hire a shop?
A: If you’re comfortable with basic welding, plumbing, and electrical work, this is a very doable weekend project. Just take your time with fuel line routing and leak testing.
Conclusion
Plumbing your66 Chevelle gas tank for EFI isn’t just about bolting on new parts—it’s about building a reliable, safe, and efficient fuel delivery system that matches the demands of modern engine management. By choosing the right tank, using ethanol-compatible materials, and following proper installation steps, you’ll enjoy smoother starts, better throttle response, and peace of mind on long drives.
Don’t let fear of complexity hold you back. Thousands of Chevelle owners have made this upgrade successfully—and you can too.
Found this guide helpful? Share it with your fellow gearheads on Facebook, Reddit (r/chevelle), or Instagram! Tag #ChevelleEFI to inspire others in the classic car community.
Drive safe, drive smart—and keep that small block purring.
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