What to Know About LS Swapping a 1994-1996 SS Impala
Make the last great Impala SS even greater with an LS engine swap!
The Last Hurrah
The 1994-1996 Chevrolet Impala SS is considered by many to be the last of the old-school high-performance sedans that used the formula of combining a comfortable family 4-door with a hot-rod V8. Subsequent generations of the Chevy Impala moved away from the front engine/rear-wheel drive layout in favor of a more economical front wheel drive setup that utilizes much smaller fuel sipping engines. The 1994-1996 Impala SS still attracts attention from car enthusiasts, but by today's standards, the 260 horsepower Corvette-based LT1 V8 is a little short on power. Since the Impala was produced in relatively large quantities and is a still a bit too new to be called a collectible classic, why not swap in an improved LS-based engine to take this hot-rod sedan up a notch or two in the performance department!
Mounts & Adapters
The Impala SS originally came equipped with a small block LT1 derived from the C4 Corvette, so any LS-based engine will fit into the engine bay without much of a fuss. That said, motor mount plates as sold by BRP Hot Rods and other vendors will be needed to properly adapt the LS block onto the Impala chassis. Similarly, you are going to want to grab a transmission mount for the particular transmission you will be using for the swap. The Impala SS did come from the factory with a 4L60E, which mates nicely to LS engines without any specialty mounts, but many have had problems with the high output of the factory LT1 breaking the transmissions thus one should at least consider beefing up the stock tranny during the engine transplant. In any case, a mount kit for the 4L60E, 4L70E, 4L80E, 4L85E, 6L80E, and 6L90E automatic transmissions, as well as various Tremec manual transmissions, are available to fit the Impala's B-body platform and ensure proper driveline angles.
Accessory Drive & Exhaust
Most folks attempting an LS swap often run into accessory drive clearance issues and end up cutting away pieces from the frame or engine bay to get everything to fit. Fortunately, the Impala does well with the stock Chevrolet/GMC truck & SUV accessory drive setup that does not require notching the frame or cross member as the F-body or Corvette setups do. If you do not plan to run air-conditioning, the entire truck setup will drop straight in, but if AC is to be used, minor clearance of the ac bracket to the passenger motor mount will be needed.
As for exhaust headers, there seems to be an endless amount of options for a LS-swapped Impala. Basically, any stock set of exhaust manifolds provide ample clearance, but many opt for various F-body long tube headers. Similarly, Hedman/BRP have come together to offer several different sets of mid-length and long tube headers in various diameters and sizes to fit with your engine and transmission combo. In any case, once the headers are in, it is just a matter of running the rest of the exhaust system out the back of the car.
Cooling, Fueling, and Oil Pan
Most LS swaps typically involve replacing the radiator to keep the new engine cool, but the stock Impala SS unit has proven quite robust and is an effective method of cooling moderate LS builds. Simply put, it is just a matter routing new coolant hoses from the radiator to the inlet and outlet on the LS engine.
The fuel system setup is quite easily addressed with a replacement Walbro 255 in-tank fuel pump. Similarly, companies such as Racetronix offer their own fuel pump that drops right into the stock fuel tank and supplies the correct fuel pressure required by various LS engines. One thing to note is that the fuel pump wiring had a tendency to corrode and cause voltage drops resulting in low fuel pressure on the older Impalas, so be sure the wiring is in good shape to avoid potential issues.
Another area of note is the oil pan. Most standard LS engine oil pans will have clearance issues with the crossmember, so a low profile oil pan, such as Moroso's LS High Clearance Oil Pan, will provide the additional room required for the swap.
Electrical
With all of the additional electronics used for an LS engine application, an ECM and accompanying wiring harness will be needed to get it up and running. Perhaps the easiest solution is to purchase an ECM & wiring harness made for your engine and transmission combo from one of the many EFI specialists (Speartech, BP Automotive, LSX4U, Hot Rod Harness). These companies can typically tune the ECM to your specific application and disable any security features if necessary. An alternative, but much more labor-intensive method of wiring up an LS engine, is to integrate the LS ECM into the OEM harness. The level of work required will vary between Gen III and Gen IV engines, but suffice it to say that it can be done and there are some good enthusiast-created walkthroughs articles on the subject.
For help with service of your car, check out the how-to section of LS1Tech.com