GM G-body cars (1978–1988) were built with classic style, but most left the factory with the underwhelming 305 small-block. Swapping in a 350 SBC or modern LS engine turns these cars into serious street or strip machines. This guide walks through the parts, challenges, pros/cons, and what you actually need to make the swap successful.
Popular G-Body Swap Platforms
Chevrolet Monte Carlo / SS / Aerocoupe
Buick Regal / Grand National / T-Type
Oldsmobile Cutlass Supreme / 442
Pontiac Grand Prix
Why Swap the 305?
Unless you’re going with a bone-stock restoration, there isn’t a great list of reasons to keep the stock 305 under the hood. These engines have:
Poor power potential
Small bore limits cylinder head choices
Weak bottom end and low compression
A 350 or LS opens the door to modern power, better aftermarket support, and easier tuning. Think more power for less money.
G-Body Engine Swap Options
| Swap Option | Power Range | Cost | Difficulty | Notes |
|---|---|---|---|---|
| 350 Small Block | 300–450 hp | $ | Easy | Direct fit with minimal wiring |
| LS-Based Swap | 350–600+ hp | $$–$$$ | Moderate | Modern EFI, more power potential |
Parts Needed For Both Swaps
| Component | 350 Swap | LS Swap |
|---|---|---|
| Motor mounts | Stock / conversion | LS adapter mounts |
| Transmission | TH350/TH400 fine | Often needs 4L60E/4L80E |
| Headers | G-body SBC headers | G-body or universal LS headers |
| Fuel system | Stock carb OK | EFI pump + return line |
| Wiring | Minimal | Standalone harness/TX swap harness |
| Driveshaft | Usually fine | May need shortening |
| Crossmember | May need mod | Needs LS-specific crossmember |
| Cooling system | Stock OK | Aluminum rad + steam port |
| Accessory drive | SBC brackets | LS accessory kit or junkyard |
G-Body 350 SBC Swap – Details
Swapping in a 350, or any other SBC is basically a direct bolt-in. It’s the easiest choice if you want more power with minimal rewiring or having to buy new parts.
Can reuse many stock accessories
Available crate engines or junkyard options
Works well with TH350/TH400 trans
Carb or EFI both work
Cost-effective and still easy to work on. Great for street builds or budget performance.
G-Body LS Swap – Details
More power, better tuning, modern reliability.
But you’ll need:
Fuel injection (high-pressure pump + return line)
Wiring harness (standalone recommended)
PCM flashed to remove security and emissions controls
Accessory drive solution (F-body & Corvette fit well)
Transmission planning (overdrive is ideal for cruising)
Steam port and correct radiator
Motor mount adapters and correct oil pan for clearance
Transmission Considerations
| Transmission | Works With | Notes |
|---|---|---|
| TH350 | SBC | No overdrive, reliable |
| TH400 | SBC | Strong, drag preference |
| 700R4 | SBC or LS (carb) | OD + lockup converter |
| 4L60E | LS | Needs harness & PCM |
| 4L80E | LS | Strongest OD option |
Wiring & Electronics for LS Swaps
Standalone harness kits are easiest
Remove VATS (security) from PCM if using stock computer
OBD-II port lets you scan & tune
Electric fan control is easier with PCM
Cooling System
350 Swap: stock radiator generally works
LS Swap:
Aluminum radiator recommended
Must plumb LS steam port line
Electric fan control via PCM if possible
Fuel System
350 Swap (Carb): stock fuel pump is fine
LS Swap:
Must use EFI pump (58 psi)
Return line required
Can run inline pump, in-tank pump, or drop-in G-body EFI tank
Exhaust
G-body SBC headers fit tight but available
LS swaps require G-body–specific headers or mid-length universal
Must plan O2 sensor placement
Pros and Cons of 350 or LS Swap
350 Small Block
Pros:
Cheap
Easy
Carb-friendly
Tons of parts
Cons:
Less power potential
No factory EFI without upgrades
LS Swap
Pros:
Modern EFI
Huge aftermarket
Strong blocks
Big power potential
Cons:
Requires wiring & fuel upgrades
Accessory drive and oil pan must fit
PCM needs reflash
Both swaps wake up a G-body dramatically—but they serve different goals.
350 SBC: Classic feel, easy install, budget-friendly sleeper
LS Swap: Modern muscle, reliable, scalable power
If you want 300–400 hp on a budget — go 350.
If you want 400+ hp and tuning flexibility — go LS.
Whether you go with swapping in a bigger displacement Small block or go with a modern LS, they are both great choices. Whatever route you take, make sure to hop on SS396.com for all the parts you need to make it happen, or give our friendly techs a call at (203) 235-1200!
